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Twenty-five years ago, ESA's Giotto probe swept within 600 km of Comet Halley, obtaining the first close-up images of a comet. It revealed the first evidence of organic material in a comet and, still today, much of what we know about comets comes from the pioneering mission.
Launched on 2 July 1985 by Ariane 1, Giotto was ESA's first deep-space mission, part of an ambitious international effort to solve the mysteries surrounding Comet Halley. It was also the first deep-space mission to return from an interplanetary trajectory and use Earth’s gravitational field to change orbit.
After a cruise of eight months, Giotto arrived at its destination and revealed the size and shape of Halley's nucleus. It found that the comet’s surface is very dark (one of the blackest object in the Solar System) and that it emitted jets of gas and dust.
Giotto's camera recorded many images that gave scientists a rare opportunity – the comet will not return to the inner Solar System again until 2061 – to study Halley intensively. It was particularly important to determine the comet’s composition through the readings made by Giotto as it passed through Halley’s tail.
After completing its Halley mission, Giotto went into hibernation before being woken up in the summer of 1990 for tests, and then hibernating again until early 1992.
Although a few of the instruments had been damaged during the Halley encounter, the spacecraft had survived the battering by cometary dust and was able to conduct a second flyby, this time of Comet 26P/Grigg-Skjellerup, in July 1992.
This video is a new compilation of Giotto’s historic images acquired by the Halley Multicolour Camera (HMC). It shows the comet as seen by the probe as it approached from about 900 000 km, coming to within 596 km.
The images were processed by the HMC team led by Uwe Keller at the Max Planck Institute for Solar System Research (MPS/Lindau). Together with B. Grieger from the Rosetta team at ESA/ESAC, they produced this video in 2011 to mark the 25th anniversary of Giotto's flyby.
Images and video credit/copyright: © MPS 1986–2011 | 0.859341 | 3.703358 |
by Kim Malville
Venus is low in the southwest throughout September and deserves watching, getting into various encounters with Spica, the Moon, and Saturn.
September 5/6: Look for first magnitude star Spica twinkling madly below Venus
September 8: Venus and the moon will get really close. As viewed from Brazil, Argentina, Uruguay, and Chile, the moon will occult Venus.
September 17/18: Venus moves close to Saturn.
September 22: Autumnal equinox will occur at 2:44pm when the sun crosses the celestial equator heading south.
The Perseids were good this year
As predicted, comet dust rained down last month on planet Earth in the annual Perseid meteor shower. There have been many wonderful photographs of this year’s meteor shower, but the best is by Chinese astronomer Xiang Zhan who made a series of 10 second long exposures over a period of four hours on the night of August 12/13. Combining frames of 68 meteors, he produced a this remarkable composite. Although the sand-sized comet particles are traveling parallel to each other, the resulting meteors appear to radiate from a single point on the sky in the constellation of Perseus. This illusion is the same as that of parallel railroad track, which appear to converge at a distance. If you look closely at the photo, you can see the “wish-bone” shape of Perseus. Above the radiant out of which the meteors come is the brilliant double cluster of new stars, which easily visible in the dark skies of Crestone.
For a high school project many years ago, I spent several weeks on the slopes of Mt Tamalpais overlooking San Francisco, counting Perseid meteors. Later, I was involved in a program in the Antarctic searching for bursts of faint telescopic meteors, which had once been reported at Little America. I continued to be awed by the silence and sudden brilliance of these meteors appearing without warning in the sky overhead. The brighter Perseids leave a luminous trail in their wake, making them even more memorable. These tiny fragments of dust were produced during the birth of the solar system over four billion years ago and have been gathered together in the icy embrace of comet Swift-Tuttle. All meteor showers result from comet debris, but Swift-Tuttle is one of those comets, with a diameter of 16 miles. As a result, the Swift-Tuttle tail contains many particles that are large enough to produce fireballs. Over the past six years, observers have reported about 100 fireballs (a few as brilliant as Venus) per year, more than seen in any other shower.
The Sun’s magnetic field is about to flip
Within the next few months the magnetic field of the sun is going to make a 180° turn. It’s a flip that occurs every 11 years as the sun reaches the peak of its solar cycle. The sun’s north pole has already changed sign, while the south pole is racing to catch up. Right now it is a very odd magnetic system with two positive magnetic poles.
Normally the sun is a huge N-S magnet, like our Earth. In addition it has small pockets of intense magnetic fields which make their appearance as sunspots. Our Earth’s field has small anomalies, produced by pockets of iron ore, but they are nothing compared to power of sunspots. Fortunately, the Earth’s field does not flip as frequently as the sun. The last time we flipped was about was 780,000 years ago. While a flip of the Earth’s field is a serious event since it leaves us briefly without a magnetic field to protect us from incoming charged particles (except for the protective layer of the atmosphere) there should be no great consequences for us on Earth for the sun’s flip. No need to rush out for purchase protective head gear.
Huge lava fountains are gushing from Jupiter’s moon
One of the most massive volcanic eruptions in the solar system was recently spotted on Jupiter’s moon Io, by a telescope perched, no less, on top of a volcano on Earth.
On 15 August the Keck II telescope on Mauna Kea in Hawaii recorded fountains of lava gushing from fissures in the Rarog Patera region of Io. Heated by gravitational squeezing from Jupiter and its other moons, Io is covered in volcanoes that erupt almost continuously. This particular event is easily one of the 10 largest volcanic explosions yet seen on Io by humans. The lava fountains spouted molten rock 1000 feet above Io’s surface, erupting over an area totaling 31 square kilometres. The Galileo spacecraft, which visited Jupiter from 1995 to 2003, was the last mission to get a close up view of the action on Io. Since then, monitoring of Io by Earth-based telescopes have shown how much violence a squeezed moon can produce. The biggest eruption seen so far happened in 2001, when the Keck observatory saw a lava flow that spread many hundreds of square kilometres across Io’s surface. In 2007 the New Horizons spacecraft spotted huge plumes from a volcano called Tvashtar as it flew past Io on its way to Pluto. A rocky body roughly the size of our moon, Io has relatively low gravity and almost no atmosphere, which is why its volcanic eruptions can spray molten debris much higher than those we see today on Earth. The blasts are also much more intense: an individual eruption can produce 5 terawatts of energy. The total power produced by humans on the Earth these days is about 15 terawatts. Io gives us a view of the massive volcanism that dominated the early years of Earth. It is a wonderful volcanic laboratory, although I doubt that there are many volcanologists who would care to do field work there. In addition to all the bubbling hot pots and exploding volcanoes, Io is deeply immersed in the Van Allen belts of Jupiter. High energy particles are constantly raining down on the surface of this very, very alien world. | 0.93153 | 3.586334 |
Jupiter is a happening place in the solar system. While bashful Mars only puts on a good show once every two year opposition period, and inner worlds such as Mercury and Venus yield no surface details to backyard observers at all, the cloud tops of Jupiter display a wealth of changing detail in even modest backyard telescopes.
And this month is a great time to start observing Jupiter, as the largest planet in our solar system just passed opposition on January 5th. Recently, veteran astrophotographer Michael Phillips amazed us here at Universe Today once again with a stunning time-lapse sequence of Jupiter and its moons Ganymede and Io. Now, he’s outdone himself with a new full rotation compilation of the gas giant planet.
The capture is simply mesmerizing to sit and watch. At 9.9 hours, Jupiter has the fastest rotational period of any planet in our solar system. In fact, with Jupiter currently visible low to the east at sunset, it’s possible to follow it through one rotation in the span of a single long January winter night.
We caught up with Michael recently and asked him about this amazing capture. The sequence was actually accomplished over the span of five successive evenings. This made it challenging to stitch together using a sophisticated program known as WINJupos.
“While this is possible on a long winter night when it is darker longer, I typically find it easier to do over multiple nights than one long sleepless night,” Michael told Universe Today. “If you wait too many days between observations, the features will change significantly, and then two nights will not match up clearly. The seams that result from using multiple nights are tricky to stick together. I created multiple non-overlapping seams and tried to blend them out against one another as layers in my image editing software. The result is smoother, but not quite the same as a single observation.”
A 14” f/4.5 Newtonian reflecting telescope was used for the captures. “Similar weather conditions and camera settings help quite a bit to make the multiple nights’ segments match up better,” Michael noted. “Keeping the same settings, using the same location away from my house in the corner of the yard (to reduce local atmospheric turbulence) night after night gives consistent results after removing the variability of the weather.”
Planetary photography also requires special considerations prior to imaging, such as getting Jupiter high enough in the sky and at specific longitudes to get full coverage in the rotation sequence.
“I try to consider the local weather patterns and atmospheric stability (seeing), but in reality, I pushed myself to get out as much and often as I could,” Michael told Universe Today. “Typically, I try to wait until Jupiter is at the highest in the sky, as the result is looking through less atmosphere and thus more stable conditions. Sometimes, the planets jiggle around and you just want to scream ‘SIT STILL!’ Basically around the time of opposition I go out as often as it’s clear, as those are opportunities that you don’t get back again until next year.”
Jupiter reaches opposition just over once every 13 months, moving roughly one constellation eastward each time. 2013 was an “oppositionless” year for Jupiter, which won’t occur again until 2025. Michael also notes that from his observing location at 35 degrees north latitude, Jupiter currently peaks at an altitude of 77 degrees above the horizon when it transits the local meridian. “I wasn’t going to squander it waiting for perfect conditions!”
In fact, Jupiter is currently in a region in the astronomical constellation of Gemini that will be occupied by the Sun in just over five months time during the June Solstice. Currently at a declination of around 22 degrees 45’ north, Jupiter won’t appear this high in the northern sky near opposition again until 2026.
It’s also amazing to consider the kind of results that backyard observers like Michael Phillips are now routinely accomplishing. It’s an interesting exercise to compare Michael’s capture side-by-side with a sequence captured by NASA’s New Horizons spacecraft during its 2006 flyby of Jupiter:
Both sequences capture a wealth of detail, including the enormous Great Red Spot, the Northern and Southern Equatorial Belts, and numerous white spots and smaller swirls and eddies in the Jovian atmosphere.
To date, six spacecraft (Pioneer 10 and 11, Voyagers 1 and 2, New Horizons and Cassini) have made flybys of Jupiter, and one, Galileo, orbited the planet until its demise in 2003. Juno is the next in this legacy, and will be inserted into orbit around Jupiter in July 2016.
Now is the time to get out and observe and image Jupiter and its moons, as it moves higher into the sky on successive evenings towards eastern quadrature on April 1st, 2014.
Congrats to Michael Phillips on an amazing sequence! | 0.906633 | 3.507158 |
In 2018, the Earth’s Magnetic North Pole – a wandering location where lines of magnetic force enter the Earth perpendicularly – is predicted by computer modeling of satellite data to pass closer to the Geographic North Pole than at any other time in its recorded history after English philosopher William Gilbert first calculated its existence in 1590 (published in 1600). Since then, through 1831, when British Naval Officer James Clark Ross became the first to reach it physically, and up until 1898, the Magnetic North Pole has meandered aimlessly through the islands and waterways of northern Canada. But since 1898, it has been moving steadily north-northwestward. At the beginning of the 20th century, it advanced about 5 miles each year. Then in 1970, it began to move faster. Today, the Magnetic North Pole moves about 25 miles each year. Soon, it will be at 86.471 degrees N Latitude and 178.755 degrees W Longitude, a distance less than 212 nautical miles away from the Geographic North Pole. By 2019, the Magnetic North Pole will be across the International Date Line, into the eastern hemisphere, and falling away from True North toward Siberia.
The reason we, as mariners and navigators, are interested in this is because of magnetic variation and its effect upon our ship’s compass. Variation, the “V” in “add East < T | V | M | D | C > add West”, is a force outside our ship, stemming from our position on the Earth’s surface. It is the angular difference between our geographic and magnetic meridians, expressed in degrees East or West. More simply, it is the difference in degrees between what our compass “feels” as Magnetic North versus True North. For sailors on the East Coast of the United States, the variation in the compass roses on nautical charts is West. On the West Coast, variation is East. For sailors on western Lake Superior and along the Gulf Coast off lower Alabama, there is no variation. Boats on these waters are on an agonic line where Magnetic North and True North just happen to line up on the same geographic meridian.
There are actually eight north poles. This discussion disregards five of them: the Instantaneous North Pole, the Celestial North Pole, the North Pole of Balance, the North Pole of Inaccessibility, and North Pole, Alaska. The last is a suburb of Fairbanks far from the other north poles, but it is the one important to American children at Christmas. We care about these three: the Geographic North Pole, the Magnetic North Pole, and the Geomagnetic North Pole.
First, the Geographic North Pole. This is True North, the northernmost point of the Earth as determined by the northern tip of its imaginary rotational axis. It is a mostly fixed point, subject to only thirty feet of wobble every 433 days. This is the top of the world, 90 degrees North Latitude. All the great circle meridian lines of longitude converge here, as do all of the world time zones. Standing (or floating) at this spot, North, East, and West no longer exist! The only way that explorers who vanquish these three compass cardinal points can leave the Geographic North Pole is to step South. It does not matter which way to step, because in every direction, the only direction is South.
Next, the Magnetic North Pole. The northern end of a magnetized compass needle frequently points here. It is not located at the Geographic North Pole, but it’s close enough to be useful in navigation. The reason it moves about 25 miles each year is due to earthquakes, electrical fluctuations in the Van Allen radiation belts, the ionosphere, and the magnetosphere, but it is mostly due to our planet’s internal physical structure. Earth’s magnetic field originates in its core. The inner core is probably solid iron. Surrounding the solid inner core is a molten outer core of liquid metal alloys – mostly iron and nickel – that lies about 1900 miles beneath our feet. Next out is the mantle which is solid but malleable, and then what we see every day, land and sea, is the crust. As the Earth rotates on its axis, the inner and outer cores rotate too, but each at a different rate, which creates a geo-dynamo effect. Immense heat from the inner core, hotter than the surface of the sun, caused by radioactive decay and the conversion of potential energy in heavy metals sinking down to the inner core, drives the motion of the liquid metals in the outer core. Convection currents of moving molten metals generate electrical currents that produce the Earth’s magnetic field. And because the source of the Earth’s magnetic field is moving, the Magnetic North and South Poles move as well. If the Earth’s magnetic field were generated by a large, powerful, solid, dipole (two poles), bar magnet within the solid inner core, instead of by moving molten metal alloys in the liquid outer core, the Magnetic North and South Poles would remain mostly static.
Anyway, Earth’s magnetic field emerges from the outer core vertically at the Magnetic South Pole, extends out into space, and re-enters perpendicularly, at the Magnetic North Pole. A compass needle dips there, trying to point straight down. Accordingly, this pole’s alternate name is the Magnetic Dip Pole, not to be confused with dipole. At the Magnetic South Pole, a compass needle jumps upward. I was there once by boat – the Magnetic South Pole has been off the coast of Antarctica since 1962 – and a compass needle really does try to point upward!
Last, the Geomagnetic North Pole. The electrical currents created by the convection currents of moving molten metals that generate Earth’s magnetic field are not evenly distributed throughout the liquid outer core. Due to this, the strength of Earth’s magnetic field varies from place to place underground. It is also the reason that the Magnetic North and South Poles are not antipodal, meaning that the imaginary line connecting the two does not pass straight through the center of the Earth. All of these factors combine in such ways that the parts of the Earth’s magnetic field that emerge from the bottom of the world that are not perpendicular, do not also emerge at the Magnetic South Pole as the perpendicular lines of force do. Instead, the spot where they do emerge, at the South Geomagnetic Pole, and the spot where they re-enter the planet, at the North Geomagnetic Pole, are derived mathematically as a best fit for the imaginary ends of a solid, dipolar, bar magnet that account for the properties of the Earth’s magnetic field, both on the surface and around the planet.
Once up out of the ground and above the Earth, the magnetic lines of force from the Geomagnetic South Pole, even out more uniformly. They are not perpendicular nor even all that vertical. Extending out into space, they curve northward to surround and protect the Earth from the solar wind as the magnetosphere, the northern part of which glows in the solar wind as the Northern Lights of the Aurora Borealis. North of the Arctic Circle, they curve downward once again and re-enter the Earth as the Geomagnetic North Pole, located on Ellesmere Island in Canada, northwest of Greenland, to form closed loops of magnetic force. The Geomagnetic North Pole also moves around from year to year, not as much as the Magnetic North Pole, but for the same reasons.
Although a mathematical derivation, the Geomagnetic North Pole is real enough. Like the Magnetic North Pole, the north end of a compass needle likes to point there too. Truth be told, most of the time, compass needles actually point to somewhere near the top of the world between the Magnetic and Geomagnetic North Poles. One last point, if the Earth’s magnetic field were generated by a large, imaginary, solid, dipolar, bar magnet that passed through the center of the Earth inside its solid inner core instead of by electrical currents from moving molten metals in the outer core, the Magnetic North Pole and Geomagnetic North Pole would be at the same location. The perpendicular lines of magnetic force would be at dead center, surrounded by the ones that are curved (not perpendicular).
Most compasses sold are devised to work best in the northern hemisphere. A magnetic binnacle compass has a free-spinning compass card that aligns with an agonic line or an isogonic line of the Earth’s magnetic field. Electronic fluxgate compasses measure the relative strength of electromagnetic flux passing through two coils of wire arranged perpendicularly to deduce the direction of the Earth’s magnetic field. The Earth’s magnetic field intensity is between 25,000 and 65,000 nano-teslas (0.25 to 0.65 gauss). By comparison, a strong refrigerator magnet has an intensity of about 10 million nano-teslas (100 gauss), some 150 to 400 times stronger than the Earth’s magnetic field.
Finally, about the elephant in the room. On that day back in grammar school when we sprinkled iron filings on white paper laid over a dipole magnet, we learned that magnetic lines of force flow from a magnet’s north pole to its south pole. Also, we learned that opposite poles attract and like poles repel. So, why would the Earth’s magnetic field emanate from its Magnetic South Pole and re-enter the planet at its Magnetic North Pole? And why would the north ends of magnetized needles in compasses all around the northern hemisphere want to point North? Well, it does not, and they do not! The Magnetic North Pole of the Earth is really its Magnetic South Pole! Scientists side step this fact by referring to the Magnetic North Pole as the Magnetic North Seeking Pole, as if to say that the magnetic patterns of force emanating from the Magnetic South Pole (really the Magnetic North Pole), are seeking the pole in the northern hemisphere, regardless of its polarity. The same is true of the Geomagnetic North and South Poles as well.
If this is disillusioning, it may be gratifying to learn that some scientists believe the increased rate of movement of the Magnetic North Pole may signal the early stages of a geomagnetic field reversal where the Magnetic North and South Poles would flip and exchange places, perhaps back into their “correct” positions. Rocks have revealed that at least 184 geomagnetic field reversals have occurred over the last 83 million years, roughly between every 100,000 to one million years, and that these reversals have each required between 1,000 and 10,000 years to complete. The last complete and enduring geomagnetic field reversal occurred 786,000 years ago, and it may have occurred within the span of a single human lifetime! A brief temporary reversal occurred 41,000 years ago during the Ice Age but lasted only 440 years before reverting. The hypothesized triggers of these geomagnetic field reversals are extra-terrestrial extinction-level impact events, continent-size rock slabs sinking down into the boundary between the mantle and the liquid outer core, plate tectonic subductions, or other unknown events that may have caused large-scale disruption of the moving molten metal geo-dynamo running in the liquid outer core, weakening the Earth’s magnetic field, making a re-arrangement of the Earth’s magnetic field more likely, leading even to a complete geomagnetic field reversal. | 0.811061 | 3.421717 |
A team of researchers from the Event Horizon Telescope project revealed the first image of a black hole April 10. The image was assembled from data gathered by eight radio telescopes around the world including Hawaii, Chile and Spain.
The results were announced concurrently at news conferences in Washington, D.C, and five other places around the world, according to The New York Times.
“We have been hunting this for a long time,” Jessica Dempsey, co-discoverer and deputy director of the East Asian Observatory in Hawaii, said during an interview with AP. “We have been getting closer and closer with better technology.”
Three years ago, scientists using an extraordinarily sensitive observing system heard the sound of two much smaller black holes merging to create a gravitational wave, as Einstein predicted. The new image, published in the Astrophysical Journal Letters, was announced around the world, according to AP.
Angela Speck, MU astrophysicist and director of astronomy, said the reveal of the picture marked a new step forward for the astrophysics community. It also confirmed ideas and hypotheses that were brought up in the past decades.
Speck said what makes the first image of a black hole substantial is the complex technology involved behind it.
Because of the high density of black holes, they cannot be seen through visible light but rather through radio waves.
“It is actually the giant radio dishes that are doing the observations,” Speck said. “Think about the big radio dishes you have by cable stations that provide you the satellite data. [The radio dishes used in black hole experiments] are much bigger than the ones we see in daily life. And the bigger the dishes are, they are more likely to collect things you can see.”
Essentially, researchers were trying during the project to mimic a radio dish big enough to detect all the radio waves. The intimated radio dish was equivalent to the size of the earth.
Speck said a lot of times our eyes don’t see things surrounding us not because they are not bright enough, but rather they are too close together. In this case because of the tightness of the black holes, astronomists had to place radio dishes across the globe.
Because there were images taken from various radio dishes across the globe, astronomists had to be very cautious with how to put these pieces of data together in order to composite the whole picture.
Another challenge astronomists encountered was the complexity of processing the massive amount of data within those locations.
“It took us decades to be able to have the computer capabilities that are able to combine the data within thousands of terabytes,” she said.
With the innovative data processing and telescope technologies, scientists were able to reaffirm the theories put forward in the past.
“That’s what we do in science,” she said. “Sometimes it is hard to cast the idea because the technology isn’t there for us to do the observation. When Galileo found the evidence that the Earth was in the center of the universe, no one had used telescopes to look at the universe at that time.”
Speck said the announcement was not necessarily a well-kept secret, even though there were some actions made prior in order to prevent leaks. “We didn’t know what the result was going to be like,” she said. “We knew something about the black hole was coming but that was about it.”
Speck said she wasn’t necessarily nervous before the image was revealed.
“As a scientist, quite often things don’t look like what you expected or don’t give you the answers you expect,” she said. “If it looks like what you expect, that is confirming what has been studied and build up more understanding. If it doesn’t look like what was expected, there is new science needed to be done.”
She saw it as a win-win situation, either confirming the knowledge scientists have been generating along or an opportunity to generate new knowledge.
Speck said initially the research team was trying to capture the pictures of the black holes in two different galaxies. One is located in Messier 87 galaxy, which is a more distanced galaxy from Earth, and the other is located at the core of our galaxy called Sagittarius A*.
“They couldn’t get an image at Sagittarius A even though we know there is a black hole because we can see most of the stars around it,” Speck said. She was optimistic with the future outcome of the experiment.
“I think this tells us that there is something that is going on inside the core of that black hole within that galaxy which I find interesting,” she said.
She believes this pilot image will serve as the foundation for further processes and eventually scientists will find automatic ways to process the data faster and faster.
“In this case it is confirming rather than refuting,” she said. “This is just one object we have done and we believe there are black holes in the centers of both galaxies. It will help us [further] understand how galaxies work.”
Edited by Emily Wolf | [email protected] | 0.873664 | 3.479418 |
Young Solar System Evidence Pops Up Everywhere
If the solar system formed more recently than believed, Darwinism is dead. Look how widely scattered the evidence is.
Recent cryovolcanism in Virgil Fossae on Pluto (Icarus). Distant Pluto has no reason to be young. There are no forces known to make it active. Scientists expected a dead world until New Horizons flew past it in 2015. Ammonia “lava” has been found in one region, but it’s not the only site of relatively recent activity.
- Because NH3 in its various forms is susceptible to destruction by UV photons and charged particles, its presence suggests emplacement on Pluto’s surface sometime in the past billion years.
- In addition to the debouchment of cryolava along fault lines in Virgil Fossae, fountaining from one or more associated sites appears to have distributed a mantling layer covering a few thousand square kilometers.
Keep in mind that Pluto was expected to be 4.5 billion years old. Even if the cryovolcanism were a billion years old, that approaches the last 1/5th of the time Pluto was thought to exist. What happened in the other 4/5ths, such that volcanic activity turned on in the last 20% of its existence? Also, “sometime in the past billion years” could be far more recent; the speculative estimate is based on assumptions about the amount erupted and the rate of destruction.
Titan has a belt of ice 6300 kilometres long that shouldn’t be there (New Scientist). There should not be fresh ice on the surface of Titan, because 4.5 billion years is a very long time for it to be covered up by molecules raining down from the atmosphere. Yet planetary scientists found a huge amount of it from Cassini data.
Titan has a huge ice belt near its equator, and we don’t know how it got there. Most of the surface is covered in organic sediment that constantly rains from the sky, but one corridor 6300 kilometres long – about 40 per cent of the frigid moon’s circumference – seems to be bare ice.
Ultraviolet observation of Enceladus’ plume in transit across Saturn, compared to Europa (Icarus). The plumes of Saturn’s little moon Enceladus are well-known, but those at Jupiter’s second Galilean moon Europa, one of the smoothest objects in the solar system, were discovered only recently. This paper calculates that Europa is emitting water two orders of magnitude more than Enceladus!
Saturn’s moon Enceladus is known to have a water vapor plume erupting from fissures across its south polar region. The plume was detectable in an observation of Enceladus transiting Saturn by Cassini’s Ultraviolet Imaging Spectrograph (UVIS), but only at 1216 Å (Lyman alpha). Jupiter’s moon Europa also may have multiple water vapor plumes, detected via similar ultraviolet observations of Europa transiting Jupiter (after being discovered via emission features) by Hubble Space Telescope. Comparison of the UVIS Enceladus transit observation to published Europa transit results reveals that Europa’s plumes have very different properties than Enceladus’ plume using the same observational technique. For example, the mass of water expelled is two orders of magnitude less at Enceladus compared to Europa.
If Enceladus causes headaches for belief in an old solar system, how much more Europa, erupting a hundred times as much – to say nothing of its neighbor Io, the most volcanically active body in the solar system?
How much of the sediment in Gale crater’s central mound was fluvially transported? (Geophysical Research Letters). When JPL aimed the Curiosity rover at Gale crater, they expected to find evidence of a watery flood in Mars’s past, because a mound of layered sediments in the crater were evident from orbit. Instead, the crater appeared very dry. This paper concludes that most of the sediments were not brought in by water, but by wind:
The origin of the sedimentary mound within Gale crater, the landing site for the Mars Science Laboratory rover Curiosity, remains enigmatic. Here we examine the total potential contribution of fluvial [flowing] material by conducting a volume‐based analysis. On the basis of these results, the mound can be divided into three zones: a lower, intermediate, and upper zone. The top boundary of the lowermost zone is defined by maximal contribution of water‐lain sediments, which are ~13 to 20% of the total mound volume. The upper zone is defined by the elevation of the unbreached rim to the north (–2.46 km); sediments above this elevation cannot have been emplaced by flowing water. These volume balance calculations indicate that mechanisms other than flowing water are required to account for the overwhelming majority of the sediments transported into Gale crater. The most likely candidate process is settling from eolian [wind-borne] suspension.
Mars has a lot of wind and a lot of sand. It would not require billions of years to deposit it. Notice that they speak of the “total potential contribution” by water; that’s an upper limit.
The space rock that hit the moon at 61,000 kilometers an hour (Royal Astronomical Society).
Observers watching January’s total eclipse of the Moon saw a rare event, a short-lived flash as a meteorite hit the lunar surface. Astronomers now think the space rock collided with the moon at 61,000 kilometers an hour, excavating a crater 10 to 15 meters across.
Impacts are to be expected from our knowledge of objects crossing Earth’s orbit, but how often do they impact the moon? The number of impact flashes observed in human history, which is quite a lot, has to be extrapolated over the assumed age of the solar system.
How Did the Moon End Up Where It Is? (Live Science). News watchers may find it amusing how believers in the consensus age have to tweak parameters to keep the moon old. The Darwin family gets implicated in this storytelling:
The detailed mathematics that describe this evolution were first developed by George Darwin, son of the great Charles Darwin, in 1880. But his formula produces the opposite problem when we input our modern figures. It predicts that Earth and the moon were close together only 1.5 billion years ago. Darwin’s formula can only be reconciled with modern estimates of the moon’s age and distance if its typical recent recession rate is reduced to about one centimetre per year.
The solar system owes no obligation to planetary scientists’ opinions about the ages of things. It is what it is.
If scientists followed the evidence where it leads, they would not believe that the solar system is 4.5 billion years old. That value was decided decades ago in order to give Darwin time to evolve people from bacterial ancestors. Then they found some lucky meteorites that gave them the value they liked. That has become the standard date set in stone, from which they will not be moved by contrary evidence (see 23 April 2019).
“The great” Charles Darwin. Good grief. Now read this. | 0.870939 | 3.554469 |
Titan, Saturn’s moon will be explored by the “Dragonfly” Drone
A re-locatable lander may probe the cloudy skies of Saturn’s captivating moon Titan, according to a new mission proposal.
26 Apr 2017 – Live Science
As the eight-bladed whirlybird travels across the moon, it could investigate some of the most promising potentially habitable sites on the Saturn satellite, where methane and ethane fall from the sky and flow as rivers and lakes.
The lander-size instrument, known as Dragonfly, would take advantage of Titan’s low gravity and thick atmosphere to visit multiple sites over several years, moving from one promising site to the next and recharging between the brief flights.
“It’s such a rich place to be able to explore in situ, and then it hands us the way to explore it,” the project’s principal investigator, Elizabeth Turtle, told Space.com.
Turtle, a planetary scientist at the Johns Hopkins Applied Research Laboratory in Maryland, is leading the team that’s proposing an in-depth exploration of Titan as part of NASA’s New Frontiers mission program, which generally funds midsize missions to explore the solar system.
She presented the Dragonfly concept last month at the Lunar and Planetary Sciences Conference in The Woodlands, Texas.
On Titan, flowing methane and ethane rivers and seas provide a unique opportunity to explore the chemistry that could lead to the rise of life. But it’s the thick atmosphere that would make the mission possible.
“The atmosphere is what is giving us this ability to travel on Titan,” Turtle said.
When the Cassini-Huygens mission, a joint initiative between NASA and the European Space Agency, arrived at Titan in 2004, it discovered a world where methane rained down onto the surface into organic-rich lakes and seas. It dropped the Huygens probe onto Titan’s surface, providing a tantalizing peek at some of the chemistry beneath the clouds. Over the past decade, the orbiter revealed even more details about Titan’s surface, including a variety of environments with the potential to have chemical evolution similar to Earth’s, Turtle said.
“The kind of prebiotic chemistry that we’re looking at, these are things we can’t do in the lab — the timescales are too long to do these experiments in the lab — but Titan has been doing them for ages,” Turtle said.
“The results are just sitting on the surface,” she added. “If we can get to these different places on the surface of Titan, we can pick up the results of the experiments. They’re just waiting for us.” | 0.893009 | 3.4448 |
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms (which themselves are generally referred to in non-technical language as "constellations"), which are patterns formed by prominent stars within apparent proximity to one another on Earth's night sky.
There are also numerous historical constellations not recognized by the IAU or constellations recognized in regional traditions of astronomy or astrology, such as Chinese, Hindu and Australian Aboriginal.
The Late Latin term constellātiō can be translated as "set with stars". The term was first used in astrology, of asterisms that supposedly exerted influence, attested in Ammianus (4th century). In English the term was used from the 14th century, also in astrology, of conjunctions of planets. The modern astronomical sense of "area of the celestial sphere around a specific asterism" dates to the mid 16th century.
Colloquial usage does not distinguish the senses of "asterism" and "area surrounding an asterism". The modern system of constellations used in astronomy focuses primarily on constellations as grid-like segments of the celestial sphere rather than as patterns, while the term for a star-pattern is asterism. For example, the asterism known as the Big Dipper corresponds to the seven brightest stars of the larger IAU constellation of Ursa Major.
The term circumpolar constellation is used for any constellation that, from a particular latitude on Earth, never sets below the horizon. From the north pole, all constellations north of the celestial equator are circumpolar constellations. In the northern latitudes, the informal term equatorial constellation has sometimes been used for constellations that lie to the south of the circumpolar constellations. Depending on the definition, equatorial constellations can include those that lie entirely between declinations 45° north and 45° south, or those that pass overhead between the tropics of Cancer and Capricorn. They generally include all constellations that intersect the celestial equator. | 0.806456 | 3.260614 |
Martian Ice Age Record Found
October 11, 2016
Scientists using radar data from NASA’s Mars Reconnaissance Orbiter (MRO) have found a record of the most recent Martian ice age in the planet’s north polar ice cap.
The results, published in the May 27, 2016, issue of the journal Science, agree with previous models that indicate a glacial period ended about 400,000 years ago. The research team included scientists from the Southwest Research Institute, The University of Texas Institute for Geophysics (UTIG) and Washington University.
Scientists use data from MRO’s Shallow Subsurface Radar (SHARAD)
to produce images called radargrams that show vertical slices through the layers of ice and dust that comprise the Martian polar ice deposits. For the new study, researchers analyzed hundreds of such images to look for variations in the layer properties.
On Mars, ice ages occur when–as a result of the planet’s increased tilt the planet’s poles become warmer than lower latitudes. During these periods, the polar caps retreat and water vapor migrates toward the equator, forming ground ice and glaciers at mid-latitudes. As the warm polar period ends, polar ice begins accumulating again, while ice is lost from mid-latitudes. This retreat and regrowth of polar ice is exactly what researchers see in the record revealed by the SHARAD radar images, said planetary scientist Isaac Smith, the study’s lead author.
Smith led the work while at Southwest Research Institute in Boulder,
Colorado. He came up with the idea for the research at the Jackson School of Geosciences, where he received his Ph.D. in 2013.
SHARAD is one of two radar sounders in orbit around Mars, but it is
the only one that approaches the resolution of airborne radar sounders on Earth, said Jack Holt, a study author and research professor at UTIG. The radar allowed researchers to detect and study layering within the polar caps on Mars.
“By applying basic principles of stratigraphy, we can unravel the record
of ice deposition and removal at the poles of Mars,” Holt said. | 0.853859 | 3.54943 |
Gibbous ♋ Cancer
Moon phase on 19 February 2051 Sunday is Waxing Gibbous, 9 days young Moon is in Gemini.Share this page: twitter facebook linkedin
Previous main lunar phase is the First Quarter before 1 day on 17 February 2051 at 22:16.
Moon rises in the afternoon and sets after midnight to early morning. It is visible to the southeast in early evening and it is up for most of the night.
Moon is passing about ∠20° of ♊ Gemini tropical zodiac sector.
Lunar disc appears visually 2.4% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1895" and ∠1941".
Next Full Moon is the Snow Moon of February 2051 after 6 days on 25 February 2051 at 14:53.
There is medium ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at very acute angle, so their combined tidal force is moderate.
The Moon is 9 days young. Earth's natural satellite is moving from the first to the middle part of current synodic month. This is lunation 632 of Meeus index or 1585 from Brown series.
Length of current 632 lunation is 29 days, 10 hours and 11 minutes. It is 1 hour and 4 minutes longer than next lunation 633 length.
Length of current synodic month is 2 hours and 33 minutes shorter than the mean length of synodic month, but it is still 3 hours and 36 minutes longer, compared to 21st century shortest.
This lunation true anomaly is ∠334.7°. At the beginning of next synodic month true anomaly will be ∠351.3°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
6 days after point of perigee on 12 February 2051 at 18:54 in ♓ Pisces. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 8 days, until it get to the point of next apogee on 28 February 2051 at 09:20 in ♎ Libra.
Moon is 378 296 km (235 062 mi) away from Earth on this date. Moon moves farther next 8 days until apogee, when Earth-Moon distance will reach 405 980 km (252 264 mi).
3 days after its descending node on 16 February 2051 at 04:27 in ♉ Taurus, the Moon is following the southern part of its orbit for the next 10 days, until it will cross the ecliptic from South to North in ascending node on 2 March 2051 at 09:34 in ♏ Scorpio.
16 days after beginning of current draconic month in ♏ Scorpio, the Moon is moving from the second to the final part of it.
At 14:53 on this date the Moon is meeting its North standstill point, when it will reach northern declination of ∠19.472°. Next 14 days the lunar orbit will move in opposite southward direction to face South declination of ∠-19.338° in its southern standstill point on 6 March 2051 at 08:27 in ♐ Sagittarius.
After 6 days on 25 February 2051 at 14:53 in ♍ Virgo, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.128335 |
At first glance, the narrow, 8-meter-long truss resting on its side in an assembly hall here at NASA's Goddard Space Flight Center hardly looks like a telescope - no highly polished glass mirror to focus starlight. And in an age when pixels have replaced pupils, certainly no eye-piece.
Yet the instruments mounted on the truss represent key stepping stones toward an orbiting observatory that astronomers say is critical to helping them pick up the trail of the universe's missing matter, observe the origin and evolution of chemical elements, and unravel the mysteries behind black holes - objects with gravity so intense that light fails to escape.
Known as Constellation-X, the observatory is designed to study X-ray emissions from some of the most energetic - and bizarre - objects and processes in the universe.
"The nice thing about X-ray astronomy in general is that virtually every object we study is weird," says Robert Petre, who heads up the X-ray astrophysics branch of Goddard's Laboratory for High Energy Astrophysics and is deeply involved in the Constellation-X project.
Yet, Dr. Petre adds, understanding the processes driving such objects - from neutron stars cannibalizing the matter of companion stars to the highly energetic cores of distant galaxies - is vital to understanding how the universe evolved since it burst into existence 15 billion years ago. Nor is he alone in that view.
Last May, the National Research Council published a report laying out astronomy and astrophysics projects for the next decade. Constellation-X was high on the list of "major initiatives."
Astrophysicists certainly don't lack highly capable orbiting X-ray telescopes. In 1999, the National Aeronautics and Space Administration launched the Chandra X-Ray Observatory, one of its Great Observatory series, which includes the Hubble Space Telescope.
Chandra has been a stunning success so far. For example, it has helped determine the source of X-ray emissions from the Crab Nebula, a supernova remnant in our own galaxy. And just last week, researchers using Chandra announced that they've bagged the most distant cluster of galaxies ever seen via X-rays. The cluster lies 10 billion light years from Earth. According to Harvey Tanabaum, director of the Chandra Observatory Center at the Harvard-Smithsonian Center for Astrophysics and chairman of Constellation-X's science team, Constellation-X will serve a different purpose.
More light, please
Chandra, he says, is analogous to the Hubble Space Telescope, which "does an amazing job of providing highly detailed, beautiful images from space." Yet at 2.4 meters across, Hubble's light-gathering mirror fails to capture enough light to allow astronomers to conduct detailed studies of the distant objects it images. That task falls to large ground-based "light buckets" such as the twin 10-meter Keck telescopes on Hawaii's Mauna Kea.
Constellation-X is designed to be the X-ray version of these light buckets. And its spectrograph will be able to pick more details out of the emissions it detects than can Chandra's.
As currently envisioned, the observatory would consist of four spacecraft equipped with identical X-ray telescopes whose mirrors measure 1.6 meters across. The four would orbit around a point in space 1 million to 1.5 million kilometers from Earth. By combining the images from the telescopes, which themselves would be separated by hundreds of miles, astronomers can get light-gathering results that would match a single telescope with a 6.4 meter mirror.
Dr. Tanabaum cites last week's galaxy-cluster observation to illustrate the differences. "Chandra detected about 100 X-rays from that cluster," he says, enough to allow researchers to tease an iron-like signature from Chandra's X-ray spectrograph. (The abundance of iron is a key indicator of the age of stars in a galaxy or galaxy cluster.) With the proper exposure time, Constellation-X could collect 10,000 X-rays - enough to uncover significant details in the iron signature, help establish its distribution around the cluster, and reveal information about other elements there. By looking at the ratio of iron to oxygen, for example, astronomers can reconstruct key details of the supernovae that have detonated within the galaxies, Tanabaum says.
Indeed, the metal content of distant galaxies has presented astrophysicists with a puzzle, and represents one of Constellation-X's key themes - how matter is cycled through stars, into the interstellar and intergalactic medium, then back.
"Over time, as galaxies age, heavier elements should build up" as stars' nuclear furnaces forge them from lighter elements such as hydrogen and helium, Petre explains. "But as we look farther back at more-distant clusters of galaxies, we don't see the dramatic evolution we'd expect." The problem, he continues, is that "we see little evolution" in galactic chemistry, "at least back to the point where we can look now. This suggests that all the evolution we see must have occurred earlier."
Weirder and weirder matter
Such observations have set theorists to scratching their chins and looking to Constellation-X observations for clues to the puzzle as it peers deeper into space and thus farther back in time in the hunt for chemically younger galaxies.
Goddard astrophysicist Kim Weaver adds that another theme involves the interaction of matter with intense gravitational fields, such as those presented by black holes, particularly the billion-solar-mass objects thought to lie in the heart of energetic galaxies.
These objects are known to trigger X-ray emissions as matter falls into them. "But we don't know what the ultimate source of the X-rays is," Dr. Weaver says. A leading explanation is that falling gas and dust form an accretion disk around the black hole, and as the material gets closer and speeds up, friction heats it to the million-degree temperatures needed to generate X-rays.
If all goes well, researchers hope to begin launching the Constellation-X telescopes in 2008.
(c) Copyright 2001. The Christian Science Publishing Society | 0.915704 | 3.931432 |
TESS is in the home stretch.
NASA's next planet-hunting spacecraft — whose full name is the Transiting Exoplanet Survey Satellite — is scheduled to launch on April 16 aboard a SpaceX Falcon 9 rocket from Florida's Cape Canaveral Air Force Station.
TESS will scrutinize more than 200,000 nearby stars for signs of orbiting worlds, many of which could end up being studied in detail by other observatories, mission team members said. [The Strangest Alien Planets (Gallery)]
"TESS is opening a door for a whole new kind of study," TESS project scientist Stephen Rinehart, of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. "We're going to be able to study individual planets and start talking about the differences between planets. The targets TESS finds are going to be fantastic subjects for research for decades to come. It's the beginning of a new era of exoplanet research."
If all goes according to plan, the 700-lb. (318 kilograms) TESS will settle into a highly elliptical, 13.7-day orbit that brings it as close to Earth as 67,000 miles (108,000 kilometers) and as far away as 232,000 miles (373,000 km). This orbit — which no spacecraft has ever employed before — is incredibly stable, allowing TESS to stay aloft for decades without performing any engine burns, mission officials have said.
TESS will spend its two-year prime mission using its four special cameras to hunt for "transits," the tiny brightness dips that result when alien planets cross their host stars' faces from TESS' perspective.
This is the same planet-hunting method used by NASA's Kepler space telescope, which has discovered about two-thirds of the roughly 3,700 known exoplanets. But there are some big differences between the two missions.
One is cost: Kepler's price tag was about $600 million, whereas TESS is capped at $200 million. In addition, Kepler stared continuously at a single patch of sky containing about 150,000 stars during its primary mission, which ran from 2009 through 2013. And those target stars were relatively distant — generally, more than 1,000 light-years away.
TESS will conduct a broader survey, swinging from patch to patch over two years to cover about 85 percent of the sky. And TESS will be targeting nearby stars — ones that lie within 300 light-years or so of Earth. The new mission is expected to discover thousands of new planets, some of which will be close enough to be studied in detail by other instruments, such as NASA's $8.8 billion James Webb Space Telescope, which is scheduled to launch in May 2020.
"With those larger telescopes, we'll be able to look for telltale signs in the atmospheres of those planets that might tell us what the planets are made of, and perhaps even whether they have the kinds of gases in their atmospheres that, on Earth, are an indication of life," Paul Hertz, Astrophysics Division director at NASA Headquarters, said during a news conference today (March 28).
"TESS itself will not be able to find life beyond Earth, but TESS will help us figure out where to point our larger telescopes in that search," Hertz added.
While TESS is focused on exoplanets, researchers around the world will have the chance to use the spacecraft at times to investigate other cosmic objects and phenomena via a "guest investigator" program, NASA officials said.
"I don't think we know everything TESS is going to accomplish," Rinehart said in the same statement. "To me, the most exciting part of any mission is the unexpected result, the one that nobody saw coming."
The TESS mission is managed by NASA Goddard and led and operated by the Massachusetts Institute of Technology. TESS principal investigator George Ricker is based at MIT's Kavli Institute for Astrophysics and Space Research. | 0.90831 | 3.350197 |
Event Horizon Telescope | NSF | ESO | ALMA | 2019 Apr 10
An international collaboration presents paradigm-shifting observations of the gargantuan black hole at the heart of distant galaxy M 87
The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. Today, in coordinated press conferences across the globe, EHT researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.
- Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. This long-sought image provides the strongest evidence to date for the existence of supermassive black holes and opens a new window onto the study of black holes, their event horizons, and gravity. Credit: Event Horizon Telescope Collaboration
This breakthrough was announced today in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the centre of Messier 87 , a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun .
The EHT links telescopes around the globe to form an unprecedented Earth-sized virtual telescope . The EHT offers scientists a new way to study the most extreme objects in the Universe predicted by Einstein’s general relativity during the centenary year of the historic experiment that first confirmed the theory . ...
First M87 Event Horizon Telescope Results.
- The Shadow of the Supermassive Black Hole ~ EHT Collaboration et al
- Array and Instrumentation ~ EHT Collaboration et al
- Data Processing and Calibration ~ EHT Collaboration et al
- Imaging the Central Supermassive Black Hole ~ EHT Collaboration et al
- Physical Origin of the Asymmetric Ring ~ EHT Collaboration et al
- The Shadow and Mass of the Central Black Hole ~ EHT Collaboration et al | 0.819643 | 3.682112 |
In the fall of 2006, observers at the Catalina Sky Survey in Arizona found an object orbiting the Earth. At first, it looked like a spent rocket stage — it had a spectrum similar to the titanium white paint NASA uses on rocket stages that end up in heliocentric orbits. But closer inspection revealed that the object was a natural body. Called 2006 RH120, it was a tiny asteroid measuring just a few metres across but it still qualified as a natural satellite just like the Moon. By June 2007, it was gone. Less than a year after it arrived, it left Earth’s orbit in search of a new cosmic companion.
Now, astrophysicists at Cornell are suggesting that 2006 RH120 wasn’t an anomaly; a second temporary moon is actually the norm for our planet.
Temporary satellites are a result of the gravitational pull of Earth and the Moon. Both bodies pull on one another and also pull on anything else in nearby space. The most common objects that get pulled in by the Earth-Moon system’s gravity are near Earth objects (NEOs) — comets and asteroids are nudged by the outer planets and end up in orbits that bring them into Earth’s neighbourhood.
The team from Cornell, astrophysicists Mikael Granvik, Jeremie Vaubaillon, Robert Jedicke, has modeled the way our Earth-Moon system captures these NEOs to understand how often we have additional moons and how long they stick around.
They found that the Earth-Moon system captures NEOs quite frequently. “At any given time, there should be at least one natural Earth satellite of 1-meter diameter orbiting the Earth,” the team said. These NEOs orbit the Earth for about ten months, enough time to make about three orbits, before leaving.
Luckily, and very interestingly, this discovery has implication well beyond academic applications.
Knowing that these small satellites come and go but that one is always present around the Earth, astronomers can work on detecting them. With more complete information on these bodies, specifically their position around the Earth at a given time, NASA could send a crew out to investigate. A crew wouldn’t be able to land on something a few metres across, but they could certainly study it up close and gather samples.
Proposals for a manned mission to an asteroid have been floating around NASA for years. Now, astronauts won’t have to go all the way out to an asteroid to learn about the Solar System’s early history. NASA can wait for an asteroid to come to us.
If the Cornell team is right and there is no shortage of second satellites around the Earth, the gains from such missions increases. The possible information about the solar system’s formation that we could obtain would be amazing, and amazingly cost-efficient. | 0.899682 | 3.871326 |
vendredi 11 juillet 2014
CERN - European Organization for Nuclear Research logo.
July 11, 2014
At the ATLAS experiment at CERN, physicists and engineers are testing their subdetector systems – using particles from outer space.
During its last 3-year run, the Large Hadron Collider (LHC) achieved its highest-energy collisions at 8 TeV. But when the LHC starts up again in 2015 it will hit 13 TeV, which means new challenges for the large detectors ATLAS, CMS, ALICE and LHCb. Subdetectors on the ATLAS experiment will have to be thoroughly tested for performance at high energy. But how do you test a general-purpose particle physics detector for high-energy collisions when there are no particle collisions taking place? "Cosmic rays," says ATLAS run coordinator Alessandro Polini.
These high-energy particles from outer space are mainly (89%) protons but they also include nuclei of helium (10%) and heavier nuclei (1%), all the way up to uranium. The energies of the primary cosmic rays range from around 1 GeV – the energy of a relatively small particle accelerator – to as much as 108 TeV, far higher than the beam energy of the LHC. We don’t feel them, but because they register as tracks in the ATLAS detector, physicists can use cosmic rays to calibrate and align the subdetectors when the LHC is switched off. "If there are gaps or certain tracks aren’t aligned at specific points, there is more work to be done," says Polini.
Image above: An engineer inspects the ATLAS detector during maintenance work last year (Image: Anna Pantelia/CERN).
Each subdetector is set up and tested in isolation, then joined to other subdetectors and finally installed into the whole. “It is a bit like an orchestra: the different instruments practice on their own, then we bring them together one by one," says Polini. "You need to tune and get them in the best shape possible first, only then can the ensemble work."
ATLAS took 27 inverse femtobarns of data (roughly 2 × 10 15 proton-proton collisions) during the LHC's first run, allowing for the discovery of the Higgs boson and many other results. In the second run, bunches of protons will be accelerated to nearly twice the energy and timed to collide every 25 nanoseconds in the detector. This means up to 40 million collisions per second, two times more than during the previous run.
Polini says there will be a "final rehearsal" in November with an extended cosmic-ray run when all the layers of the ATLAS detector will come together and the magnetic fields will be switched on. "ATLAS will then be ready for its symphony,” he says.
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.
Large Hadron Collider (LHC): http://home.web.cern.ch/topics/large-hadron-collider
LHC large detectors:
Image. Text, Credits: CERN / Abha Eli Phoboo.
Publié par Orbiter.ch à 17:31
NASA - Hubble Space Telescope patch.
July 11, 2014
This view, captured by the NASA/ESA Hubble Space Telescope, shows a nearby spiral galaxy known as NGC 1433. At about 32 million light-years from Earth, it is a type of very active galaxy known as a Seyfert galaxy — a classification that accounts for 10% of all galaxies. They have very bright, luminous centers that are comparable in brightness to that of our entire galaxy, the Milky Way.
Galaxy cores are of great interest to astronomers. The centers of most, if not all, galaxies are thought to contain a supermassive black hole, surrounded by a disk of in-falling material.
NGC 1433 is being studied as part of a survey of 50 nearby galaxies known as the Legacy ExtraGalactic UV Survey (LEGUS). Ultraviolet radiation is observed from galaxies, mainly tracing the most recently formed stars. In Seyfert galaxies, ultraviolet light is also thought to emanate from the accretion discs around their central black holes. Studying these galaxies in the ultraviolet part of the spectrum is incredibly useful to study how the gas is behaving near the black hole. This image was obtained using a mix of ultraviolet, visible, and infrared light.
LEGUS will study a full range of properties from a sample of galaxies, including their internal structure. This Hubble survey will provide a unique foundation for future observations with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA has already caught unexpected results relating to the center of NGC 1433, finding a surprising spiral structure in the molecular gas close to the center of NGC 1433. The astronomers also found a jet of material flowing away from the black hole, extending for only 150 light-years — the smallest such molecular outflow ever observed in a galaxy beyond our own.
For images and more information about Hubble, visit: http://www.nasa.gov/hubble and http://www.spacetelescope.org/
Image, Text, Credits: ESA/Hubble & NASA, Acknowledgements: D. Calzetti (UMass) and the LEGUS Team.
Publié par Orbiter.ch à 17:05
ESA Venus Express Mission patch.
11 July 2014
After a month surfing in and out of the atmosphere of Venus down to just 130 km from the planet’s surface, ESA’s Venus Express is about to embark on a 15 day climb up to the lofty heights of 460 km.
Since its arrival at Venus in 2006, the spacecraft has been conducting science observations from an elliptical 24-hour orbit that took it from a distant 66 000 km over the south pole – affording incredible global views – to altitudes around 250 km at the north pole, just above the top of the planet’s atmosphere.
Venus Express aerobraking
After eight years in orbit and with fuel for its propulsion system running low, a daring aerobraking campaign was planned as a final assignment for Venus Express, during which it would dip progressively lower into the atmosphere on its closest approaches to the planet.
Thus routine science operations concluded on 15 May, and the spacecraft’s altitude was allowed to drop naturally from the effect of gravity, culminating in a month ‘surfing’ between 131 km and 135 km above the surface.
Additional small thruster burns were used to drop the spacecraft to lower altitudes, reaching 130.2 km earlier this week. Tomorrow, it is expected to dip to 129.1 km.
“We have explored uncharted territory, diving deeper into the atmosphere than ever before,” says Håkan Svedhem, ESA’s Venus Express project scientist.
“We’ve measured the effects of atmospheric drag on the spacecraft, which will teach us how the density of the atmosphere varies on local and global scales.”
Indeed, the additional drag exerted by the denser atmosphere at lower altitudes reduced the spacecraft’s orbital period by more than an hour.
Small changes in the spacecraft’s acceleration were also recorded due to variations in the atmospheric density along its orbital path. Differences in acceleration were also noticed between the day and night side of the planet.
The forces experienced by the spacecraft at different altitudes equate to a difference in atmospheric density of about thousand times between 165 km and 130 km, causing significantly increased stress on the spacecraft.
Visualisation of the Venus Express aerobraking manoeuvre
Indeed, the Venus Express team monitored the rapid heating that the spacecraft experienced as it skimmed through the upper reaches of the atmosphere during each orbit at about 36 000 km/h.
“During several of the 100-second long passages through the atmosphere, the solar panel temperature sensor reading increased by over 100ºC,” describes Adam Williams, ESA’s Venus Express spacecraft operations manager.
“Analysing the spacecraft’s response to such rapid heating will be useful for planning future spacecraft systems and subsystem design.”
Commands have now been sent to the spacecraft ready to begin a series of 15 manoeuvres that will raise the lowest part of the orbit to about 460 km. These begin tomorrow and should be completed by 26 July.
Once Venus Express reaches this higher altitude orbit it will be allowed to decay naturally, eventually sinking into the atmosphere by December, ending its mission.
Image above: Visualisation of Venus Express during the aerobraking manoeuvre, which will see the spacecraft orbiting Venus at an altitude of around 130 km from 18 June to 11 July 2014.
However, it is possible that the remaining fuel will run out during the thruster burns required to raise its orbit.
If this occurs, it will no longer be possible to communicate with the craft and its orbit will once again decay.
“We have already gained valuable experience in operating a spacecraft in these challenging conditions that will be important for future missions that may require it. Once we have completed the orbit raise, we look forward to processing and analysing the scientific data collected on the atmosphere,” says Patrick Martin, ESA’s Venus Express mission manager.
For updates during the orbital raising manoeuvres follow the Rocket Science Blog and @esaoperations on Twitter.
Notes for Editors:
The recorded atmospheric density at an altitude of 165 km was 10-11 kg/m3 and at 130 km it was 10-8 kg/m3. While these values may seem small – atmospheric density at Earth’s sea level is 1 kg/m3 – the density is a thousand times greater at the lowest altitudes.
On Monday 7 July, Venus Express completed 3000 orbits around Venus.
For more information about Venus Express mission, visit: http://www.esa.int/Our_Activities/Space_Science/Venus_Express
Rocket Science Blog: http://blogs.esa.int/rocketscience/
Images, Video, Text, Credits: ESA / C. Carreau.
Publié par Orbiter.ch à 16:52
ESA - XMM-Newton Mission patch.
11 July 2014
ESA’s XMM-Newton observatory has helped to uncover how the Universe’s first stars ended their lives in giant explosions.
Astronomers studied the gamma-ray burst GRB130925A – a flash of very energetic radiation streaming from a star in a distant galaxy 5.6 billion light years from Earth – using space- and ground-based observatories.
Exploding blue supergiant star
They found the culprit producing the burst to be a massive star, known as a blue supergiant. These huge stars are quite rare in the relatively nearby Universe where GRB130925A is located, but are thought to have been very common in the early Universe, with almost all of the very first stars having evolved into them over the course of their short lives.
But unlike other blue supergiants we see nearby, GRB130925A's progenitor star contained very little in the way of elements heavier than hydrogen and helium. The same was true for the first stars to form in the Universe, making GRB130925A a remarkable analogue for similar explosions that occurred just a few hundred million years after the Big Bang.
“There have been several theoretical studies predicting what a gamma-ray burst produced by a primordial star would look like,” says Luigi Piro of the Istituto Astrofisica e Planetologia Spaziali in Rome, Italy, and lead author of a new paper appearing in The Astrophysical Journal Letters. “With our discovery, we’ve shown that these predictions are likely to be correct.”
Astronomers believe that primordial stars were very large, perhaps several hundred times the mass of the Sun. This large bulk then fuelled ultralong gamma-ray bursts lasting several thousand seconds, up to a hundred times the length of a ‘normal’ gamma-ray burst.
Indeed, GRB130925A had a very long duration of around 20 000 seconds, but it also exhibited additional peculiar features not previously spotted in a gamma-ray burst: a hot cocoon of gas emitting X-ray radiation and a strangely thin wind.
Both of these phenomena allowed astronomers to implicate a blue supergiant as the stellar progenitor. Crucially, they give information on the proportion of the star composed of elements other than hydrogen and helium, elements that astronomers group together under the term ‘metals’.
After the Big Bang, the Universe was dominated by hydrogen and helium and therefore the first stars that formed were very metal-poor. However, these first stars made heavier elements via nuclear fusion and scattered them throughout space as they evolved and exploded.
This process continued as each new generation of stars formed, and thus stars in the nearby Universe are comparatively metal-rich.
Finding GRB130925A's progenitor to be a metal-poor blue supergiant is significant, offering the chance to explore an analogue of one of those very first stars at close quarters. Dr Piro and his colleagues speculate that it might have formed out of a pocket of primordial gas that somehow survived unaltered for billions of years.
As a nearby counterpart, however, GRB130925A has offered astronomers the opportunity to gain some insight into these first stars today.
“XMM-Newton’s space-based location and sensitive X-ray instruments were key to observing the later stages of this blast, several months after it first appeared,” says ESA's XMM-Newton project scientist Norbert Schartel.
XMM-Newton x-ray observatory
“At these times, the fingerprints of the progenitor star were clearer, but the source itself was so dim that only XMM-Newton’s instruments were sensitive enough to take the detailed measurements needed to characterise the explosion.”
A number of space- and ground-based missions were involved in the discovery and characterisation of GRB130925A. Alongside the XMM-Newton observations, the astronomers involved in this study also used X-ray data gathered at different times with NASA’s SwiftBurst Alert Telescope, and radio data from the CSIRO's Australia Telescope Compact Array.
“Combining these observations was crucial to get a full picture of this event,” added Eleonora Troja of NASA’s Goddard Space Flight Center in Maryland, USA, a co-author of the paper.
“This new understanding of GRB130925A means that we now have strong indications how a primordial explosion might look — and therefore what to search for in the distant Universe,” says Dr Schartel.
The search will require powerful facilities. The NASA/ESA/CSA James Webb Space Telescope, an infrared successor to the Hubble Space Telescope due for launch in 2018, and ESA’s planned Athena mission, a large X-ray observatory following on from XMM-Newton in 2028, will both have key roles to play.
Notes for Editors:
“A Hot Cocoon in the Ultralong GRB 130925A: Hints of a PopIII-like Progenitor in a Low Density Wind Environment” by L. Piro et al. is published in The Astrophysical Journal Letters.
GRB130925A triggered the SwiftBurst Alert Telescope on 25 September 2013 at 04:11:24 GMT. Early gamma-ray emission was detected by Integral, and the burst was subsequently observed by the Fermi Gamma-Ray Burst Monitor, Konus-Wind, Swift’s X-ray telescope, Chandra, the Gamma-Ray Burst Optical/Near-Infrared Detector, the Hubble Space Telescope and the CSIRO's Australia Telescope Compact Array. GRB130925A was located in a galaxy so far away that its light has been travelling for 3.9 billion years.
ESA’s XMM-Newton was launched in December 1999. The largest scientific satellite to have been built in Europe, it is also one of the most sensitive X-ray observatories ever flown. More than 170 wafer-thin, cylindrical mirrors direct incoming radiation into three high-throughput X-ray telescopes. XMM-Newton's orbit takes it almost a third of the way to the Moon, allowing for long, uninterrupted views of celestial objects.
XMM-Newton overview: http://www.esa.int/Our_Activities/Space_Science/XMM-Newton_overview
XMM-Newton image gallery: http://xmm.esac.esa.int/external/xmm_science/gallery/public/index.php
XMM-Newton in-depth: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=23
Images, Text, Credits: ESA/NASA/Swift/A. Simonnet, Sonoma State Univ.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 06:09
jeudi 10 juillet 2014
ESA - Hubble Space Telescope logo.
10 July 2014
Hubble snaps a violent galactic merger and chain of star formation
Droplets of star formation and two merging galaxies in SDSS J1531+3414
The Universe is filled with objects springing to life, evolving and dying explosive deaths. This new image from the NASA/ESA Hubble Space Telescope captures a snapshot of some of this cosmic movement. Embedded within the egg-shaped blue ring at the centre of the frame are two galaxies. These galaxies have been found to be merging into one and a "chain" of young stellar superclusters are seen winding around the galaxies’ nuclei.
Image above: Wide field image of the region around two merging galaxies in SDSS J1531+3414 (ground based telescope).
At the centre of this image lie two elliptical galaxies, part of a galaxy cluster known as [HGO2008]SDSS J1531+3414, which have strayed into each other’s paths. While this region has been observed before, this new Hubble picture shows clearly for the first time that the pair are two separate objects. However, they will not be able to hold on to their separate identities much longer, as they are in the process of merging into one .
Image above: Hubble Space Telescope photographed a 100,000-light-year-long structure that looks like a string of pearls twisted into a corkscrew shape winds around the cores of the two massive galaxies. The “pearls” are superclusters of blazing, blue-white, newly born stars. Image Credit: NASA/ESA.
Finding two elliptical galaxies merging is rare, but it is even rarer to find a merger between ellipticals rich enough in gas to induce star formation. Galaxies in clusters are generally thought to have been deprived of their gaseous contents; a process that Hubble has recently seen in action. Yet, in this image, not only have two elliptical galaxies been caught merging but their newborn stellar population is also a rare breed.
The stellar infants — thought to be a result of the merger — are part of what is known as "beads on a string" star formation. This type of formation appears as a knotted rope of gaseous filaments with bright patches of new stars and the process stems from the same fundamental physics which causes rain to fall in droplets, rather than as a continuous column .
Zooming in on merging galaxies and a string of star formation in SDSS J1531+3414
Nineteen compact clumps of young stars make up the length of this "string", woven together with narrow filaments of hydrogen gas. The star formation spans 100,000 light years, which is about the size of our galaxy, the Milky Way. The strand is dwarfed, however, by the ancient, giant merging galaxies that it inhabits. They are about 330,000 light years across, nearly three times larger than our own galaxy. This is typical for galaxies at the centre of massive clusters, as they tend to be the largest galaxies in the Universe.
The electric blue arcs making up the spectacular egg-like shape framing these objects are a result of the galaxy cluster’s immense gravity. The gravity warps the space around it and creates bizarre patterns using light from more distant galaxies.
Panning across merging galaxies and a string of star formation in SDSS J1531+3414
Astronomers have ruled out the possibility that the blue strand is also just a lensed mirage from distant galaxies and now their challenge is to understand the origin of the cold gas that is fuelling the growth of the stellar superclusters. Was the gas already in the merging galaxies? Did it condense like rain from the rapidly cooling X-ray plasma surrounding the two galaxies? Or, did it cool out of a shock in the X-ray gas as the ten-million-degree gaseous halos surrounding the galaxies collided together? Future observations with both space- and ground-based observatories are needed to unravel this mystery.
Water droplet animation and the link to stellar superclusters
Mergers occur when two or more galaxies stray too close to one another, causing them to coalesce into one large body (heic0912). The violent process strips gas, dust and stars away from the galaxies involved and can alter their appearances dramatically, forming large gaseous tails, glowing rings, and warped galactic discs (heic0810).
The merging system is forming stellar superclusters in equally spaced beads just like evenly spaced drops from a tap. The only real difference is that surface tension in the falling water is analogous to gravity in the context of the star-forming chain. This is a wonderful demonstration that the fundamental laws of physics really are scale-invariant - we see the same physics in rain drops that we do on 100 000 light-year scales.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
NASA release: http://hubblesite.org/newscenter/archive/releases/2014/26
Hubblecast 76: Merging galaxies and droplets of starbirth: http://www.spacetelescope.org/videos/heic1414a/
For images and more information about Hubble, visit: http://www.nasa.gov/hubble and http://www.spacetelescope.org/
Images, Text, Credits: NASA, ESA/Hubble and G. Tremblay (European Southern Observatory)/Digitized Sky Survey (DSS).
Acknowledgement: M. Gladders & M. Florian (University of Chicago, USA), S. Baum, C. O'Dea & K. Cooke (Rochester Institute of Technology, USA), M. Bayliss (Harvard-Smithsonian Center for Astrophysics, USA), H. Dahle (University of Oslo, Norway), T. Davis (European Southern Observatory), J. Rigby (NASA Goddard Space Flight Center, USA), K. Sharon (University of Michigan, USA), E. Soto (The Catholic University of America, USA) and E. Wuyts (Max-Planck-Institute for Extraterrestrial Physics, Germany).
Videos Credits: Directed by: Georgia Bladon/Visual design and editing: Martin Kornmesser/Written by: Nicky Guttridge and Georgia Bladon/Narration: Sara Mendes da Costa/Images: NASA, ESA/Videos: NASA, ESA/Dripping water video (04:33): Dirk Essl/Galaxy formation animation (04:44): Klaus Dolag (MPA, Garching)/Music: Steve Buick/Web and technical support: Mathias Andre and Raquel Yumi Shida/Executive producer: Lars Lindberg Christensen.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 17:04
NASA - Mars Reconnaissance Orbiter (MRO) logo.
July 10, 2014
Repeated high-resolution observations made by NASA’s Mars Reconnaissance Orbiter (MRO) indicate the gullies on Mars’ surface are primarily formed by the seasonal freezing of carbon dioxide, not liquid water.
The first reports of formative gullies on Mars in 2000 generated excitement and headlines because they suggested the presence of liquid water on the Red Planet, the eroding action of which forms gullies here on Earth. Mars has water vapor and plenty of frozen water, but the presence of liquid water on the neighboring planet, a necessity for all known life, has not been confirmed. This latest report about gullies has been posted online by the journal Icarus.
"As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," said lead author Colin Dundas of the U.S. Geological Survey's Astrogeology Science Center in Flagstaff, Arizona. "We were able to get many more observations, and as we started to see more activity and pin down the timing of gully formation and change, we saw that the activity occurs in winter."
Image above: This pair of images covers one of many sites on Mars where researchers use the HiRISE camera on NASA's Mars Reconnaissance Orbiter to study changes in gullies on slopes. Changes such as the ones visible in deposits near the lower end of this gully occur during winter and early spring on Mars. Image Credit: NASA/JPL.
Dundas and collaborators used the High Resolution Imaging Science Experiment (HiRISE) camera on MRO to examine gullies at 356 sites on Mars, beginning in 2006. Thirty-eight of the sites showed active gully formation, such as new channel segments and increased deposits at the downhill end of some gullies.
Using dated before-and-after images, researchers determined the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water.
Frozen carbon dioxide, commonly called dry ice, does not exist naturally on Earth, but is plentiful on Mars. It has been linked to active processes on Mars such as carbon dioxide gas geysers and lines on sand dunes plowed by blocks of dry ice. One mechanism by which carbon dioxide frost might drive gully flows is by gas that is sublimating from the frost providing lubrication for dry material to flow. Another may be slides due to the accumulating weight of seasonal frost buildup on steep slopes.
The findings in this latest report suggest all of the fresh-appearing gullies seen on Mars can be attributed to processes currently underway, whereas earlier hypotheses suggested they formed thousands to millions of years ago when climate conditions were possibly conducive to liquid water on Mars.
Dundas's co-authors on the new report are Serina Diniega of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, and Alfred McEwen of the University of Arizona, Tucson.
Image above: This pair of before (left) and after (right) images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter documents formation of a new channel on a Martian slope between 2010 and 2013. Image Credit: NASA/JPL-Caltech/Univ. of Arizona.
"Much of the information we have about gully formation, and other active processes, comes from the longevity of MRO and other orbiters,” said Diniega. “This allows us to make repeated observation of sites to examine surface changes over time."
Although the findings about gullies point to processes that do not involve liquid water, possible action by liquid water on Mars has been reported in the past year in other findings from the HiRISE team. Those observations were of a smaller type of surface flow feature.
An upcoming special issue of Icarus will include multiple reports about active processes on Mars, including smaller flows that are strong indications of the presence of liquid water on Mars today.
"I like that Mars can still surprise us," Dundas said. "Martian gullies are fascinating features that allow us to investigate a process we just don't see on Earth."
HiRISE is operated by the University of Arizona, Tucson. The instrument was built by Ball Aerospace & Technologies Corp. of Boulder, Colorado. JPL manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate in Washington.
For more information about HiRISE, visit: http://hirise.lpl.arizona.edu
Additional information about MRO is online at: http://www.nasa.gov/mro
For recent findings suggesting the presence of liquid water on Mars, visit: http://go.nasa.gov/1q1VRLS
Images (mentioned), Text, Credits: NASA / J.D. Harrington / JPL / Guy Webster.
Publié par Orbiter.ch à 16:28
ESA - Rosetta Mission patch.
July 10, 2014
Postcards from space as Rosetta draws closer to its destination comet
Comet on 4 July 2014
Comet 67P/Churyumov-Gerasimenko, taken by the narrow angle camera of Rosetta’s scientific imaging system, OSIRIS, on 4 July 2014, at a distance of 37 000 km. The three images are separated by 4 hours, and are shown in order from left to right. The comet has a rotation period of about 12.4 hours. It covers an area of about 30 pixels, and although individual features are not yet resolved, the image is beginning to reveal the comet’s irregular shape.
For more information about Rosetta Mission, visit: http://www.esa.int/Our_Activities/Space_Science/Rosetta
Images, Text, Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.
Publié par Orbiter.ch à 16:18
ESA / Arianespace - Flight VS08 Mission poster.
July 10, 2014
Soyuz Flight VS08
Launch of Soyuz and 03b satellites network
O3b Networks’ mission to bridge the digital divide marked a significant step forward with today’s Arianespace Soyuz flight that deployed its next four connectivity satellites – which will complete the basic constellation for this customer’s pioneering connectivity service and help make the O3b vision a reality.
The launch success – which had a total payload lift performance of more than 3,200 kg. – continues the partnership between Arianespace and O3b Networks, and builds upon the on-target Soyuz mission that orbited O3b’s initial four spacecraft in June 2013.
Arianespace launches O3b satellites on Soyuz mission
Soyuz is the medium-lift member of Arianespace’s launcher family operated from French Guiana, joined by the heavy-lift Ariane 5 and lightweight Vega. For today’s mission, it delivered O3b Networks’ satellites during a flight lasting 2 hours and 22 minutes – which included three burns of the Fregat upper stage, with the four passengers released in two phases from a dispenser system.
The latest O3b Networks connectivity satellites are equipped with Ka-band transponders, and will be positioned at a medium-orbit altitude of 8,062 km. Along with the four spacecraft launched last year, they form the network framework to provide billions of consumers and businesses in nearly 180 countries with low-cost, high-speed, low-latency Internet and mobile connectivity.
First release in target orbit of the 03b 2 and 4 satellites
O3b Networks’ satellite constellation is fully scalable to meet market demand and operates from a medium-orbit altitude of 8,062 km. From this low altitude, latency is dramatically reduced – bringing it on par with a long-haul fiber transmission. The O3b spacecraft were designed, integrated and tested by Thales Alenia Space.
Arianespace continues to set the standard in launch services worldwide. With the Soyuz, Ariane 5 and Vega launchers fully operational at the Spaceport in French Guiana, it is the only launch services company capable of delivering any payload into any orbit – from the smallest spacecraft to the largest geostationary satellites, as well as satellite clusters for constellations and cargo missions to the International Space Station.
Second release in target orbit of the 03b 1 and 3 satellites
Today’s Soyuz success marked the medium-lift vehicle’s eighth flight from the Spaceport since its 2011 introduction at French Guiana, as well as the fifth Arianespace mission from this equatorial launch site in 2014.
Artist's view of the 03b satellites network constellation in orbit
The next mission in Arianespace’s 2014 manifest is the July 24 Ariane 5 flight that will deliver Europe’s fifth, and final, Automated Transfer Vehicle (ATV) for servicing of the International Space Station. The ATV program – managed by the European Space Agency (ESA) – is part of Europe’s contribution to the International Space Station’s operation.
Relive the first moments of Flight VS08 on YouTube: https://www.youtube.com/watch?v=kAWxLQ7rH5o
See the Arianespace VS08 launch kit for further details: http://www.arianespace.com/news-launch-kits/2013-2014-archive.asp
O3b Networks website: http://www.o3bnetworks.com/homepage.aspx
Blog for O3b Networks: http://www.o3bnetworks.com/additional-pages/blog
Thales Alenia Space website: http://www.thalesgroup.com/space
Arianespace website: http://www.arianespace.com/index/index.asp
Images, Video, Text, Credits: Arianespace / Arianespace TV / Alenia Space / Screen captures: Orbiter.ch Aerospace.
Publié par Orbiter.ch à 15:10
ESA - Mars Express Mission patch.
10 July 2014
The surface of Mars is pocked and scarred with giant impact craters and rocky ridges, as shown in this new image from ESA’s Mars Express that borders the giant Hellas basin in the planet’s southern hemisphere.
The Hellas basin, some 2300 km across, is the largest visible impact structure in the Solar System, covering the equivalent of just under half the land area of Brazil.
Perspective view of Hellespontus Montes
The images presented here were taken on 13 January 2014 by the high-resolution stereo camera on Mars Express and feature a portion of the western rim of the Hellas basin, which slopes into the foreground.
This view highlights the Hellespontus Montes, a rough chain of mountain-like terrain that runs around the rim of the basin, seen here as an uneven ridge curving across the top of the main colour, topography and 3D images, and extending to the right in the perspective view.
Hellespontus Montes in context
This feature is a product of the final stages of the formation of the vast Hellas impact basin itself, most likely as the basin walls – which were first pushed outwards by the extraordinary forces at work during the formation of the basin – later collapsed and sank inwards to create the observed stair-stepped shape.
Several craters throughout the scene display wrinkled and rippled features: the close-up of the crater in the foreground of the perspective view highlights a particularly interesting example where the wrinkles form a roughly concentric pattern, with ever-smaller arcs towards the structure’s centre.
Hellespontus Montes topography
This type of feature is known as ‘concentric crater fill’, and is thought to be associated with snowfall and freezing cycles in an earlier and wetter period of martian history.
During this period, snow fell and covered the surface and later moved downhill into the crater. Once inside the crater, the snow became trapped and soon covered by surface dust, before compacting to form ice.
The number of concentric lines indicates many cycles of this process and it is possible that craters like these may still be rich in ice hidden beneath just tens of metres of surface debris.
Meanwhile, the largest impact crater in the image (top left in the main colour, topography and 3D images) shows a degraded, layered crater deposit with several ‘islands’ of material that have been eroded by powerful winds.
Here and elsewhere in the scene, the formation of dunes building up around impact structures and at the base of Hellespontus Montes further indicates the role of strong winds shaping this scene.
Hellespontus Montes in 3D
Last but certainly not least, intricate valleys lead down from the Hellespontus Montes and weave through and across the smoother surrounding plains.
This complex region shows that many of nature’s forces have left their mark here over time, from the formation of the Hellas basin billions of years ago, to the slow and steady changes created by wind and snowfall over millions of years.
High Resolution Stereo Camera: http://berlinadmin.dlr.de/Missions/express/indexeng.shtml
Behind the lens...: http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Behind_the_lens
Frequently asked questions: http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Frequently_asked_questions
ESA Planetary Science archive (PSA): http://www.rssd.esa.int/PSA
NASA Planetary Data System: http://pds-geosciences.wustl.edu/missions/mars_express/hrsc.htm
HRSC data viewer: http://hrscview.fu-berlin.de/
Mars Express top 10 discoveries: http://sci.esa.int/jump.cfm?oid=51820
Images, Text, Credits: ESA / DLR / FU Berlin / NASA MGS MOLA Science Team / Freie Universitaet Berlin.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 05:35
mercredi 9 juillet 2014
NASA - Messenger Mission to Mercury patch / NASA - STEREO Mission logo.
July 9, 2014
Understanding the sun from afar isn't easy. How do you figure out what powers solar flares – the intense bursts of radiation coming from the release of magnetic energy associated with sunspots – when you must rely on observing only the light and particles that make their way to near-Earth’s orbit?
One answer: you get closer. NASA's MESSENGER spacecraft -- which orbits Mercury, and so is as close as 28 million miles from the sun versus Earth's 93 million miles -- is near enough to the sun to detect solar neutrons that are created in solar flares. The average lifetime for one of these neutrons is only 15 minutes. How far they travel into space depends on their speed, and slower neutrons don't travel far enough to be seen by particle detectors in orbit around Earth. Results showing that MESSENGER has likely observed solar neutrons appeared in the Journal of Geophysical Research: Space Physics on July 9, 2014.
Image above: A solar flare erupted on the far side of the sun on June 4, 2011, and sent solar neutrons out into space. Solar neutrons don't make it to all the way to Earth, but NASA's MESSENGER, orbiting Mercury, found strong evidence for the neutrons, offering a new technique to study these giant explosions. Image Credit: NASA/STEREO/Helioviewer.
"To understand all the processes on the sun we look at as many different particles coming from the sun as we can – photons, electrons, protons, neutrons, gamma rays –to gather different kinds of information," said David Lawrence, first author of the paper at The Johns Hopkins Applied Physics Lab in Laurel, Maryland. "Closer to Earth we can observe charged particles from the sun, but analyzing them can be a challenge as their journey is affected by magnetic fields."
Such charged particles twirl and gyrate around the magnetic field lines created by the vast magnetic systems that surround the sun and Earth. Neutrons, however, as they are not electrically charged, travel in straight lines from the flaring region. They can carry information about flare processes unperturbed by the environment through which they move. This information can be used by scientists to decipher one aspect of the complicated acceleration processes that are responsible for the creation of highly energetic and fast solar particles.
Lawrence and his team looked at MESSENGER data from June 4 and 5, 2011, corresponding to solar flares that were accompanied by fast-moving, energetic charged particles. The flare occurred on the far side of the sun so Earth-based views of the flare region could not be obtained. However, a solar telescope on NASA's Solar Terrestrial Relations Observatory, or STEREO, spacecraft did have a clear view of the far-side flare region. STEREO provided useful observations of the flare. This combined use of NASA mission data makes each individual mission more effective in addressing unsolved science questions.
The MESSENGER data showed an increase in the number of – not electrically charged -- neutrons at Mercury’s orbit hours before the large number of charged particles reached the spacecraft. This indicated that the neutrons were most likely produced by accelerated flare particles striking the lower solar atmosphere, releasing neutrons as a result of high-energy collisions. So, together, the MESSENGER and STEREO data can provide new information about how particles are accelerated in solar flares.
For more information about MESSENGER, visit: http://www.nasa.gov/messenger
For information about STEREO, visit: http://www.nasa.gov/stereo
Image (mentioned), Text, Credits: NASA's Goddard Space Flight Center / Karen C. Fox.
Publié par Orbiter.ch à 14:14
ESO - European Southern Observatory logo.
9 July 2014
New observations reveal how stardust forms around a supernova
Artist’s impression of dust formation around a supernova explosion
A group of astronomers has been able to follow stardust being made in real time — during the aftermath of a supernova explosion. For the first time they show that these cosmic dust factories make their grains in a two-stage process, starting soon after the explosion, but continuing for years afterwards. The team used ESO's Very Large Telescope (VLT) in northern Chile to analyse the light from the supernova SN2010jl as it slowly faded. The new results are published online in the journal Nature on 9 July 2014.
The origin of cosmic dust in galaxies is still a mystery . Astronomers know that supernovae may be the primary source of dust, especially in the early Universe, but it is still unclear how and where dust grains condense and grow. It is also unclear how they avoid destruction in the harsh environment of a star-forming galaxy. But now, observations using ESO’s VLT at the Paranal Observatory in northern Chile are lifting the veil for the first time.
An international team used the X-shooter spectrograph to observe a supernova — known as SN2010jl — nine times in the months following the explosion, and for a tenth time 2.5 years after the explosion, at both visible and near-infrared wavelengths . This unusually bright supernova, the result of the death of a massive star, exploded in the small galaxy UGC 5189A.
The dwarf galaxy UGC 5189A, site of the supernova SN 2010jl
“By combining the data from the nine early sets of observations we were able to make the first direct measurements of how the dust around a supernova absorbs the different colours of light,” said lead author Christa Gall from Aarhus University, Denmark. “This allowed us to find out more about the dust than had been possible before.”
The team found that dust formation starts soon after the explosion and continues over a long time period. The new measurements also revealed how big the dust grains are and what they are made of. These discoveries are a step beyond recent results obtained using the Atacama Large Millimeter/submillimeter Array (ALMA), which first detected the remains of a recent supernova brimming with freshly formed dust from the famous supernova 1987A (SN 1987A; eso1401).
The team found that dust grains larger than one thousandth of a millimetre in diameter formed rapidly in the dense material surrounding the star. Although still tiny by human standards, this is large for a grain of cosmic dust and the surprisingly large size makes them resistant to destructive processes. How dust grains could survive the violent and destructive environment found in the remnants of supernovae was one of the main open questions of the ALMA paper, which this result has now answered — the grains are larger than expected.
The dwarf galaxy UGC 5189A, site of the supernova SN 2010jl (annotated)
“Our detection of large grains soon after the supernova explosion means that there must be a fast and efficient way to create them,” said co-author Jens Hjorth from the Niels Bohr Institute of the University of Copenhagen, Denmark, and continued: “We really don’t know exactly how this happens.”
But the astronomers think they know where the new dust must have formed: in material that the star shed out into space even before it exploded. As the supernova's shockwave expanded outwards, it created a cool, dense shell of gas — just the sort of environment where dust grains could seed and grow.
Results from the observations indicate that in a second stage — after several hundred days — an accelerated dust formation process occurs involving ejected material from the supernova. If the dust production in SN2010jl continues to follow the observed trend, by 25 years after the supernova, the total mass of dust will be about half the mass of the Sun; similar to the dust mass observed in other supernovae such as SN 1987A.
“Previously astronomers have seen plenty of dust in supernova remnants left over after the explosions. But they also only found evidence for small amounts of dust actually being created in the supernova explosions. These remarkable new observations explain how this apparent contradiction can be resolved,” concludes Christa Gall.
Cosmic dust consists of silicate and amorphous carbon grains — minerals also abundant on Earth. The soot from a candle is very similar to cosmic carbon dust, although the size of the grains in the soot are ten or more times bigger than typical grain sizes for cosmic grains.
Light from this supernova was first seen in 2010, as is reflected in the name, SN 2010jl. It is classed as a Type IIn supernova. Supernovae classified as Type II result from the violent explosion of a massive star with at least eight times the mass of the Sun. The subtype of a Type IIn supernova — “n” denotes narrow — shows narrow hydrogen lines in its spectra. These lines result from the interaction between the material ejected by the supernova and the material already surrounding the star.
This research was presented in a paper “Rapid formation of large dust grains in the luminous supernova SN 2010jl”, by C. Gall et al., to appear online in the journal Nature on 9 July 2014.
The team is composed of Christa Gall (Department of Physics and Astronomy, Aarhus University, Denmark; Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark; Observational Cosmology Lab, NASA Goddard Space Flight Center, USA), Jens Hjorth (Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark), Darach Watson (Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark), Eli Dwek (Observational Cosmology Lab, NASA Goddard Space Flight Center, USA), Justyn R. Maund (Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast, UK; Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark; Department of Physics and Astronomy, University of Sheffield, UK), Ori Fox (Department of Astronomy, University of California, Berkeley, USA), Giorgos Leloudas (The Oskar Klein Centre, Department of Physics, Stockholm University, Sweden; Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark), Daniele Malesani (Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark) and Avril C. Day-Jones (Departamento de Astronomia, Universidad de Chile, Chile).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1421/eso1421a.pdf
ALMA Spots Supernova Dust Factory: http://www.eso.org/public/news/eso1401/
More about X-Shooter: http://www.eso.org/sci/facilities/paranal/instruments/xshooter.html
More about the VLT: http://www.eso.org/public/teles-instr/vlt/
Images, Text, Credits: ESO / M. Kornmesser.
Publié par Orbiter.ch à 13:43
mardi 8 juillet 2014
NASA - Mars Reconnaissance Orbiter (MRO) patch / NASA - Mars Science Laboratory (MSL) patch.
July 8, 2014
NASA Mars rover Curiosity has driven out of the ellipse, approximately 4 miles wide and 12 miles long (7 kilometers by 20 kilometers), that was mapped as safe terrain for its 2012 landing inside Gale Crater.
The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter photographed the rover on June 27 at the end of a drive that put Curiosity right on the ellipse boundary. An image from that observation is online at: http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA18399
NASA's Mars Reconnaissance Orbiter spacecraft. Image Credit: NASA/JPL-Caltech
The landing ellipse is the area within which the rover had a very high probability of touching down when it arrived at Mars on Aug. 5, 2012, PDT (Aug. 6, UTC). The area needed to meet requrements for providing access to scientifically interesting sites while presenting few landing hazards, such as steep slopes or large boulders. Many areas of scientific interest have slopes ineligible for landing safety, and Curiosity was designed to have the capability of driving far enough to get to slopes ouside of the landing ellipse. Since landing, Curiosity has driven slightly more than 5 miles (8 kilometers).
Image above: This June 27, 2014, image from the HiRISE camera on NASA's Mars Reconnaissance Orbiter shows NASA's Curiosity Mars rover on the rover's landing-ellipse boundary, which is superimposed on the image. The 12-mile-wide ellipse was mapped as safe terrain for its 2012 landing inside Gale Crater. Image Credit: NASA/JPL-Caltech/Univ. of Arizona.
NASA's Mars Science Laboratory (MSL), alias "Curiosity" rover. Image Credit: NASA/JPL-Caltech
NASA's Mars Science Laboratory Project is using Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter and Mars Science Laboratory projects for NASA's Science Mission Directorate in Washington. HiRISE is operated by the University of Arizona, Tucson. The instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colorado.
For more information about the Mars Reconnaissance Orbiter, which has been studying Mars from orbit since 2006, visit: http://www.nasa.gov/mro
For more information about Curiosity, visit: http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/
You can follow the mission on Facebook at: http://www.facebook.com/marscuriosity and on Twitter at: http://www.twitter.com/marscuriosity
Images (mentioned), Text, Credits: NASA / JPL / Guy Webster.
Best regards, Orbiter.ch
Publié par Orbiter.ch à 13:33
Soyuz-2.1b with these payloads on the lanch-pad
July 8 at 19 hours 58 minutes Moscow time from the launch complex Sq. 31 took the Baikonur Cosmodrome launch vehicle (LV) Soyuz-2.1b with the upper stage (RB) Frigate spacecraft (SC) Meteor-M № 2 and six small spacecraft MCA-FCI «SkySat-2», «DX-1», «TechDemoSat-1», «UKube-1», «AISSAT-2."
From the Baikonur Cosmodrome launch of spacecrafts Meteor-M № 2 and six small satellites
In accordance with cyclogram flight 20 hour 07 minutes after the regular department head unit from the third stage booster RB Fregat continued removal of spacecraft into the desired orbit.
Meteor-M № 2 is intended to provide timely global hydrometeorological information for weather forecasting, monitoring of the ozone layer and radiation environment in near-Earth space, as well as for monitoring the sea surface, determine its temperature, including ice conditions for the purpose of navigation in the polar areas. Spacecraft mass is 2778 kg, payload weight is approximately equal to 1250 kg, lifetime - 5 years.
Meteor-M № 2 satellite
Spacecraft Meteor-M successfully launched into the target orbit
In accordance with cyclogram flight Meteor-M № 2 (production of JSC "Corporation VNIIEM") displayed on the target orbit.
Trail of the Soyuz rocket into the skies of Baikonur
He will join the existing national meteorological orbital grouping. Meteor-M № 2 is designed for the global and local images of clouds, the earth's surface, ice and snow cover data to determine sea surface temperature and the radiation temperature of the underlying surface, the earth's surface radar images, data on the distribution of ozone in the atmosphere and its overall content, information about the geophysical conditions in near-Earth space.
Rocket Soyuz-2.1b created in JSC "RCC" Progress (Samara) and is a modification of Soyuz-2. Compared to option "1a" she has an engine with high power characteristics for the third stage. The Soyuz-2.1b in relation to a previous version of the above injection accuracy, stability and control, increased payload weight. Upper stage Fregat made in FSUE "NPO. Lavochkin".
ROSCOSMOS Press Release: http://www.federalspace.ru/20761/ and http://www.federalspace.ru/20762/
Images, Text, Credits: Roscosmos press service / ROSCOSMOS / Translation: Orbiter.ch Aerospace.
Publié par Orbiter.ch à 12:42
NASA / ESA - Cassini Mission to Saturn patch.
July 8, 2014
Vortex and Rings
The Cassini spacecraft captures three magnificent sights at once: Saturn's north polar vortex and hexagon along with its expansive rings.
The hexagon, which is wider than two Earths, owes its appearance to the jet stream that forms its perimeter. The jet stream forms a six-lobed, stationary wave which wraps around the north polar regions at a latitude of roughly 77 degrees North.
This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 2, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.
The view was obtained at a distance of approximately 1.4 million miles (2.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 43 degrees. Image scale is 81 miles (131 kilometers) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .
The Cassini ESA wesite: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens
Image, Text, Credits: NASA / JPL-Caltech / Space Science Institute.
Publié par Orbiter.ch à 08:52
lundi 7 juillet 2014
NASA - Voyager-1 Mission patch.
July 7, 2014
NASA's Voyager 1 spacecraft has experienced a new "tsunami wave" from the sun as it sails through interstellar space. Such waves are what led scientists to the conclusion, in the fall of 2013, that Voyager had indeed left our sun's bubble, entering a new frontier.
"Normally, interstellar space is like a quiet lake," said Ed Stone of the California Institute of Technology in Pasadena, California, the mission's project scientist since 1972. "But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later. The wave causes the plasma surrounding the spacecraft to sing."
Voyager 1 Entering Interstellar Space (Artist Concept)
Image above: This artist's concept depicts NASA's Voyager 1 spacecraft entering interstellar space, or the space between stars. Interstellar space is dominated by the plasma, or ionized gas, that was ejected by the death of nearby giant stars millions of years ago. Image Credit: NASA/JPL-Caltech.
Data from this newest tsunami wave generated by our sun confirm that Voyager is in interstellar space -- a region between the stars filled with a thin soup of charged particles, also known as plasma. The mission has not left the solar system -- it has yet to reach a final halo of comets surrounding our sun -- but it broke through the wind-blown bubble, or heliosphere, encasing our sun. Voyager is the farthest human-made probe from Earth, and the first to enter the vast sea between stars.
"All is not quiet around Voyager," said Don Gurnett of the University of Iowa, Iowa City, the principal investigator of the plasma wave instrument on Voyager, which collected the definitive evidence that Voyager 1 had left the sun's heliosphere. "We're excited to analyze these new data. So far, we can say that it confirms we are in interstellar space."
Our sun goes through periods of increased activity, where it explosively ejects material from its surface, flinging it outward. These events, called coronal mass ejections, generate shock, or pressure, waves. Three such waves have reached Voyager 1 since it entered interstellar space in 2012. The first was too small to be noticed when it occurred and was only discovered later, but the second was clearly registered by the spacecraft's cosmic ray instrument in March of 2013.
Voyager Captures Sounds of Interstellar Space
Video above: The first two tsunami waves to reach Voyager 1 caused surrounding ionized matter to ring like a bell at frequencies expected in interstellar space. The third tsunami caused similar ringing, confirming that Voyager 1 continues it journey into interstellar space. Video Credit: NASA's Voyager 1 spacecraft captured these sounds of interst.
Cosmic rays are energetic charged particles that come from nearby stars in the Milky Way galaxy. The sun's shock waves push these particles around like buoys in a tsunami. Data from the cosmic ray instrument tell researchers that a shock wave from the sun has hit.
Meanwhile, another instrument on Voyager registers the shock waves, too. The plasma wave instrument can detect oscillations of the plasma electrons.
"The tsunami wave rings the plasma like a bell," said Stone. "While the plasma wave instrument lets us measure the frequency of this ringing, the cosmic ray instrument reveals what struck the bell -- the shock wave from the sun."
This ringing of the plasma bell is what led to the key evidence showing Voyager had entered interstellar space. Because denser plasma oscillates faster, the team was able to figure out the density of the plasma. In 2013, thanks to the second tsunami wave, the team acquired evidence that Voyager had been flying for more than a year through plasma that was 40 times denser than measured before -- a telltale indicator of interstellar space.
Why is it denser out there? The sun's winds blow a bubble around it, pushing out against denser matter from other stars.
Now, the team has new readings from a third wave from the sun, first registered in March of this year. These data show that the density of the plasma is similar to what was measured previously, confirming the spacecraft is in interstellar space. Thanks to our sun's rumblings, Voyager has the opportunity to listen to the singing of interstellar space -- an otherwise silent place.
Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. Both spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and Neptune. Voyager 2, launched before Voyager 1, is the longest continuously operated spacecraft and is expected to enter interstellar space in a few years.
JPL, a division of Caltech, built and operates the twin Voyager spacecraft. The Voyagers Interstellar Mission is a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington. NASA's Deep Space Network, managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. The spacecraft's nuclear batteries were provided by the Department of Energy.
For more information on the Voyager mission, visit: http://voyager.jpl.nasa.gov
Image (mentioned), Video (mentioned), Text, Credits: NASA / JPL / Whitney Clavin.
Publié par Orbiter.ch à 17:10 | 0.954063 | 3.580319 |
NASA Goddard Space Flight Center logo.
Nov. 30, 2018
In the next decade, NASA aims to launch humankind toward the Moon and on to Mars — a monumental step in crewed space travel. Such a journey is filled with challenges and perils, not unlike those faced by the first explorers to cross the ocean. However, instead of stormy seas, these explorers will set sail amid the hazards of the heliosphere — the magnetic environment emanating out from the Sun and encompassing the solar system. The risks of travelling through this realm ultimately ride on how well we can understand the dynamics therein.
Moon, Mars and beyond... Image Credit: NASA
“In order to get to Mars, spacecraft and humans will be immersed in the heliosphere and will have to contend with it,” said Terry Onsager, program scientist at NASA Headquarters in Washington, D.C. “That environment can be a harsh one, but one we’re ready for.”
To safely navigate the heliosphere, NASA scientists and missions have been mapping the region for decades. Recent results, from near-Earth to far across the solar system, are helping us engineer a safe path for future space explorers abroad.
Staying Safe En Route to Mars
As astronauts leave the protective magnetic bubble around Earth — the magnetosphere — they become exposed to damaging energetic particle radiation from the Sun. Continually streaming out from the solar surface, these solar energetic particles, as they are known, can reach levels that can damage electronics and harm living tissue in space.
Animation above: This simulation of a July 14, 2000, coronal mass ejection shows the CME and subsequent solar energetic particles streaming out away from the Sun. The Sun’s magnetic field lines are shown in magenta and white. The flux of protons with energies greater than 50 MeV is shown in color. Animation Credits: Predictive Science Inc./University of New Hampshire/NASA Goddard/Joy Ng.
“Periodically, solar eruptions on the Sun’s surface can generate enormous increases in the energetic particle radiation environments, and when that occurs, systems need to be able to handle that,” Onsager said.
Spacecraft are being designed with radiation-hardened equipment and safe areas for the astronauts to hide during solar storms -- which can last hours to days. In addition to these protective securities, having a reliable warning system is paramount to astronaut safety.
NASA’s Solar Dynamics Observatory — SDO — has kept constant vigil on the Sun for eight years. The images it takes in visible and ultraviolet light allow scientists to continually monitor surface conditions and understand what activity might be roiling just below, ready to emerge. Once an eruption is seen on the Sun’s surface, astronauts can typically be given about a half-hour advance warning before the incoming radiation reaches peak levels. While this provides astronauts with some time to take action, ultimately improvements in space weather forecasting are needed to provide more advanced warning.
Improving Space Weather Forecasting
Predicting space weather — the billowing solar wind and solar energetic particles it carries — is not unlike terrestrial weather forecasting. It starts with observing the Sun — which SDO and other NASA heliophysics missions do around the clock. Data about the Sun’s activity is then fed into physics-based computer models that make statistical predictions about the probability of a solar eruption. This then allows scientists to give warning when such an event may occur.
“Forecasting space weather phenomena, whether at Earth or in deep space, is very, very complex,” said Jingnan Guo, heliophysicist at the University of Kiel in Germany. “We have to consider scales from the Sun-Earth distance — about 93 million miles, at which waves and erupted material propagate across space — to below a few meters, at which scale you see the turbulence and kinematics of the particles.”
As of now, our understanding of the complex dynamics at play in the heliosphere is incomplete, making predictions difficult; the best models are still in the early stages of development. Scientists who model space weather depend on NASA’s many heliophysics missions to improve their forecasts.
“If you have just a single point observation, it’s very hard to model or even, sometimes, interpret the data. If you have multiple points, than you can constrain your model and make sure the underlying theories are capable of reproducing that event,” said Leila Mays, a space weather scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Last year, a strong solar energetic particle event was observed by multiple NASA missions. The results, which record the first particle event seen at ground level on both Mars and Earth, were recently published in the journal Space Weather. In this event, high-energy particles accelerated by an intensive shock driven by a coronal mass ejection — a violent blast on the solar surface that spews out gas and energetic particles — were first detected as they left the Sun with SDO. The scientists used ground-based instruments and models to track how material moved through the heliosphere and to measure their intensity upon reaching Earth and Mars.
The CME Heard 'Round the Solar System
Video above: The Sept. 10, 2017, coronal mass ejection event — shown here by the largest red blast — was seen by multiple missions across the solar system, helping scientists understand how this type of potentially harmful radiation may impact future space explorers as they travel to the Moon and Mars. Video Credits: CCMC/NASA Goddard/Tom Bridgman.
Such multi-point observations are essential in understanding how particles blasted off the Sun travel through the solar system. This knowledge of how radiation spreads ultimately helps improve models — giving astronauts more advanced warning of potentially dangerous space weather events.
“Although this is the biggest solar energetic particle event we’ve observed on the surface of Mars, it would not have been hazardous for astronauts there,” said Guo, who authored the paper. “However, much larger solar energetic particle events are possible and this event helps us understand what that might look like.”
Scientists will continue to study space weather from Earth with ground-based instruments as well as NASA’s heliophysics fleet of spacecraft, but future missions will provide new viewpoints.
“Ultimately, more data is needed and we’re hoping to get some from Parker Solar Probe, since it’s going so close to the Sun, where these harmful particles are accelerated to high energies,” Mays said. “We have assumptions of how this acceleration works that go into the models, but measurements from Parker would really help improve our theories.”
Already, the Radiation Assessment Detector Instrument aboard the Curiosity Rover has been measuring high-energy radiation on the Martian surface — data that is helping scientists understand how much radiation humans will be exposed to when visiting the red planet. NASA and NOAA’s joint Geostationary Operational Environmental Satellite Program has been measuring energetic particle measurements for current astronauts since the 1980s. Instruments to study particle radiation will also be aboard future flights and the Lunar Orbital Platform-Gateway, the proposed outpost to orbit the Moon.
“Future deep-space human exploration vehicles provide not only the ability to safeguard the crew onboard, but simultaneously do new scientific experiments,” said Antti Pulkkinen, scientist at NASA’s Goddard Space Flight Center. “They will serve this dual purpose.”
These measurements will benefit more than just space weather forecasting. They will also help us understand things closer to home — like the Moon.
New Insight at the Moon
Returning to the Moon will undoubtedly unlock new doors to understanding our nearest neighbor in space. After all, it wasn’t until we first stepped foot on the Moon that we were able to understand its origins. Today we are still discovering new things and NASA missions like the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon’s Interaction with the Sun — ARTEMIS — are uncovering new insights into the Moon’s tenuous atmosphere.
The Moon is, in fact, not airless. It has a thin atmospheric layer — the exosphere — composed mainly of hydrogen, helium, neon and argon, extends about a hundred miles above the surface. Mixed on the upper edge of the exosphere is a tenuous and ephemeral secondary layer — the ionosphere — created by sunlight energizing atoms in the exosphere.
Image above: The moon has a tenuous atmosphere, called an exosphere, extending a few hundred miles above the surface. Sunlight ionizes a portion of this exosphere, producing an ionosphere roughly one million times weaker than Earth’s. Image Credits: NASA's Goddard Space Flight Center/Mary Pat Hrybyk-Keith.
“The ionosphere is a million times less dense than the ionosphere of Earth so it’s really hard to directly measure those charged particles,” said Jasper Halekas, ARTEMIS scientist at the University of Iowa in Iowa City, and lead author on a new study of the Moon’s ionosphere.
Using a new technique to analyze data from ARTEMIS, Halekas and his team were able to measure the ionosphere directly. They noted the ionosphere enlarged every full Moon and became coupled with Earth’s ionosphere — meaning charged particles are likely able to travel back and forth between the two bodies’ ionospheres.
“The presence of the Moon may actually affect Earth’s magnetosphere,” Halekas said. “It might actually perturb that local environment.”
New missions to the Moon would allow the study of the ionosphere and exosphere from the surface, giving us a better understanding of that coupling and how our atmosphere may be linked with the Moon’s.
The new results might also help us better understand how atmospheres are created and sustained on small bodies.
“The same technique could be applied to lots of other bodies in the solar system, which should have a tenuous atmosphere like the Moon’s,” Halekas said. “This would include: moons around the outer planets, big bodies in the asteroid belt, things in the Kuiper belt, and even objects outside the solar system.”
Setting Off with Confidence
It is hard to foretell the discoveries that will be made as humankind voyages to the Moon and Mars, though certainly they will be innumerable. What is certain is the starring role heliophysics will play in helping us get there. Studying heliophysics and space weather are invaluable to protecting our astronauts and assets in space. And, undoubtedly, this journey across the solar system will help us uncover new discoveries about the heliosphere we call home, making the roads of space safer for future generations of space explorers.
Learn more about NASA’s Moon to Mars Program: https://www.nasa.gov/topics/moon-to-mars
Learn more about NASA’s Solar Dynamics Observatory: https://www.nasa.gov/sdo
Learn more about NASA’s research on the Sun-Earth environment: https://www.nasa.gov/mission_pages/sunearth/index.html
Learn more about NASA’s ARTEMIS mission: https://www.nasa.gov/artemis
GOES (Geostationary Environmental Operational Satellites): http://www.nasa.gov/goes/
Mars Science Laboratory or MSL (Curiosity): https://www.nasa.gov/mission_pages/msl/index.html
Lunar Orbital Platform-Gateway: https://www.nasa.gov/topics/moon-to-mars/lunar-outpost/
Space Weather: https://doi.org/10.1029/2018SW001973
Goddard Space Flight Center (GSFC): https://www.nasa.gov/centers/goddard/home/index.html
Images (mentioned), Animation (mentioned), Video (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Mara Johnson-Groh. | 0.817143 | 3.548759 |
What if you could stand at the top of a volcano and peer out across the universe? It the timing is right, you might see an amazing panorama like the one featured here
. In this case, the volcano is the Hawaii's Mauna Kea
, and the time was a clear night last summer In the foreground of this south-facing panorama lies a rugged landscape
dotted with rocks and hardy plants
. Slightly above and further out, a white blanket
of clouds spreads horizontally to the horizon, seemingly dividing heaven and Earth. City lights illuminate the clouds and sky on the far left, while orange lava in the volcanic caldera of Kilauea
lights up the clouds just left of center. The summit of an even more distant Hawaiian volcano, Mauna Loa
, is visible in dark silhouette near the central horizon. Green airglow
is visible above the clouds, caused by air molecules excited
by the Sun during the day. The Moon is the bright orb on the right. A diffuse band of light-colored zodiacal light
extends up from the far right. Most distant, the dramatic central band
of our Milky Way Galaxy
appears to rise vertically from Mauna Loa. The person
who witnessed and captured this breathtaking panorama stands before you in the image center.
The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.
This week the shadow of the New Moon fell on planet Earth, crossing Queensland's Cape York in northern Australia ... for the second time in six months. On the morning of May 10, the Moon's apparent size was too small to completely cover the Sun though, revealing a "ring of fire" along the central path of the annular solar eclipse. Near mid-eclipse from Coen, Australia, a webcast team captured this telescopic snapshot of the annular phase. Taken with a hydrogen-alpha filter, the dramatic image finds the Moon's silhouette just within the solar disk, and the limb of the active Sun spiked with solar prominences. Still, after hosting back-to-back solar eclipses, northern Australia will miss the next and final solar eclipse of 2013. This November, a rare hybrid eclipse will track across the North Atlantic and equatorial Africa.
The Super Moon wins, by just a little, when its apparent size is compared to the Sun in this ingenious composite picture. To make it, the Full Moon on May 6 was photographed with the same camera and telescope used to image the Sun (with a dense solar filter!) on the following day. Of course, on May 6 the Moon was at perigee, the closest point to Earth in its eliptical orbit, making it the largest Full Moon of 2012. Two weeks later, on May 20, the Moon will be near apogee, the most distant point in its orbit, so by then it will be nearly at its smallest apparent size. It will also be a dark New Moon on that date. And for some the New Moon will be surprisingly easy to compare to the Sun, because on May 20 the first solar eclipse of 2012 will be visible from much of Asia, the Pacific, and North America. Along a path 240 to 300 kilometers wide, the eclipse will be annular. Near apogee the smaller silhouetted Moon will fit just inside the bright solar disk.
Undulating bright ridges and dusty clouds cross this close-up of the nearby star forming region M8, also known as the Lagoon Nebula. A sharp, false-color composite of narrow band visible and broad band near-infrared data from the 8-meter Gemini South Telescope, the entire view spans about 20 light-years through a region of the nebula sometimes called the Southern Cliff. The highly detailed image explores the association of many newborn stars imbedded in the tips of the bright-rimmed clouds and Herbig-Haro objects. Abundant in star-forming regions, Herbig-Haro objects are produced as powerful jets emitted by young stars in the process of formation heat the surrounding clouds of gas and dust. The cosmic Lagoon is found some 5,000 light-years away toward constellation Sagittarius and the center of our Milky Way Galaxy. (Editor's Note: For location and scale, check out this image superimposing the close-up region shown in today's APOD on the larger Lagoon Nebula. Scale image is courtesy R. Barbá.)
Why is this giant crater on Mimas oddly colored? Mimas, one of the smaller round moons of Saturn, sports Herschel crater, one of the larger impact craters in the entire Solar System. The robotic Cassini spacecraft now orbiting Saturn took the above image of Herschel crater in unprecedented detail while making a 10,000-kilometer record close pass by the icy world just over one month ago. Shown in contrast-enhanced false color, the above image includes color information from older Mimas images that together show more clearly that Herschel's landscape is colored slightly differently from more heavily cratered terrain nearby. The color difference could yield surface composition clues to the violent history of Mimas. An impact on Mimas much larger than the one that created the 130-kilometer Herschel would likely have destroyed the entire world.
Where do meteors come from? Visible meteors are typically sand-sized grains of ice and rock that once fragmented from comets. Many a meteor shower has been associated with a known comet, although some intriguing orphan showers do remain. Recently, a group of meteor enthusiasts created a network of over 100 video cameras placed at 25 well-separated locations across Japan. This unprecedented network recorded not only 240,000 optically bright meteors over two years, but almost 40,000 meteors seen by more than one station. These multiple-station events were particularly interesting because they enabled the observers to extrapolate meteor trajectories back into the Solar System. The resulting radiant map is shown above, with many well known meteor showers labelled by the first three letters of the home constellation. Besides known meteor showers, eleven new showers were identified by new radiants on the sky from which meteors appear to flow. The meteor sky is ever changing, and it may be possible that new shower radiants will appear in the future. Research like this could also potentially identify previously unknown comets or asteroids that might one day pass close to the Earth.
Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars in Earth's sky is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars as they orbit around the Sun. During the most recent such pass over the last year, the proximity of Mars made the red planet appear larger and brighter than usual. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop in the sky. Near the top of the loop, Earth passed Mars and the retrograde motion was the highest. Retrograde motion can also be seen for other Solar System planets.
The silhouette of an intriguing dark nebula inhabits this cosmic scene, based on images from the Palomar Observatory Sky Survey. Lynds' Dark Nebula (LDN) 1622 appears against a faint background of glowing hydrogen gas only easily seen in long telescopic exposures of the region. LDN 1622 lies near the plane of our Milky Way Galaxy, close on the sky to Barnard's Loop - a large cloud surrounding the rich complex of emission nebulae found in the Belt and Sword of Orion. But the obscuring dust of LDN 1622 is thought to be much closer than Orion's more famous nebulae, perhaps only 500 light-years away. At that distance, this 1 degree wide field of view would span less than 10 light-years.
As dawn approached on May 8, astronomer Stefan Seip carefully watched Fragment C of broken comet 73P/Schwassmann-Wachmann 3 approach M57 - the Ring Nebula, and faint spiral galaxy IC 1296. Of course, even though the trio seemed to come close together in a truly cosmic photo opportunity, the comet is in the inner part of our solar system, a mere 0.5 light-minutes or so from Seip's telescope located near Stuttgart, Germany, planet Earth. The Ring Nebula (upper right) is more like 2,000 light-years distant, well within our own Milky Way Galaxy. At a distance of 200 million light-years, IC 1296 (between comet and ring) is beyond even the Milky Way's boundaries. Because the comet is so close, it appears to move relatively rapidly against the distant stars. This dramatic telescopic view was composited from two sets of images; one compensating for the comet's apparent motion and one recording the background stars and nebulae.
This floating ring is the size of a galaxy. In fact, it is part of the photogenic Sombrero Galaxy, one of the largest galaxies in the nearby Virgo Cluster of Galaxies. The dark band of dust that obscures the mid-section of the Sombrero Galaxy in optical light actually glows brightly in infrared light. The above image shows the infrared glow, recently recorded by the orbiting Spitzer Space Telescope, superposed in false-color on an existing image taken by NASA's Hubble Space Telescope in optical light. The Sombrero Galaxy, also known as M104, spans about 50,000 light years across and lies 28 million light years away. M104 can be seen with a small telescope in the direction of the constellation of Virgo.
M13 is one of the most prominent and best known globular clusters. Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13. The reason for the low abundance of unusual blue straggler stars in M13 is currently unknown.
M83 is one of the closest and brightest spiral galaxies on the sky. Visible with binoculars in the constellation of Hydra, majestic spiral arms have prompted its nickname as the Southern Pinwheel. Although discovered 250 years ago, only much later was it appreciated that M83 was not a nearby gas cloud, but a barred spiral galaxy much like our own Milky Way Galaxy. M83, pictured above in a photograph from a Very Large Telescope, is a prominent member of a group of galaxies that includes Centaurus A and NGC 5253, all of which lie about 15 million light years distant. To date, six supernova explosions have been recorded in M83. An intriguing double circumnuclear ring has been discovered at the center of M83.
What could you see approaching Saturn aboard an interplanetary cruise ship? Your view would likely resemble this subtly shaded image of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute, the Cassini spacecraft. Cassini flew by Jupiter at the turn of the millennium and is scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth.
A drop of water or prism of glass can spread out visible sunlight into a rainbow of colors. In order of increasing energy, the well known spectrum of colors in a rainbow runs red, orange, yellow, green, blue, indigo, violet. X-ray light too can be spread out into a spectrum ordered by energy ... but not by drops of water or glass. Instead, the orbiting Chandra X-ray Observatory uses a set of 540 finely ruled, gold gratings to spread out the x-rays, recording the results with digital detectors. The resulting x-ray spectrum reveals much about the compositions, temperatures, and motions within cosmic x-ray sources. This false color Chandra image shows the x-ray spectrum of a star system in Ursa Major cataloged as XTE J1118+480 and thought to consist of a sun-like star orbiting a black hole. Unlike the familiar appearance of a prism's visible light rainbow, the energies here are ordered along radial lines with the highest energy x-rays near the center and lowest energies near the upper left and lower right edges of the image. The central spiky region itself is created by x-rays from the source which are not spread out by the array of gratings.
Can this be a spiral galaxy? In fact, NGC 3314 consists of two large spiral galaxies which just happen to almost exactly line-up. The foreground spiral is viewed nearly face-on, its pinwheel shape defined by young bright star clusters. But against the glow of the background galaxy, dark swirling lanes of interstellar dust are also seen to echo the face-on spiral's structure. The dust lanes are surprisingly pervasive, and this remarkable pair of overlapping galaxies is one of a small number of systems in which absorption of visible light can be used to directly explore the distribution of dust in distant spirals. NGC 3314 is about 140 million light-years away in the southern constellation of Hydra. Just released, this color composite was constructed from Hubble Space Telescope images made in 1999 and 2000.
Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form.
Callisto's surface has many stories to tell. The most distant of Jupiter's Galilean Moons, Callisto shows the highest density of impact craters in the Solar System, but harbors no volcanoes or even any large mountains. Callisto's surface is laced with cracks and craters from billions of years of collisions with interplanetary debris. This image shows Callisto's true colors, and was taken in November 1997 by the robot spacecraft Galileo currently orbiting Jupiter.
The Great Nebula in Orion, an immense, nearby starbirth region, is probably the most famous of all astronomical nebulae. Here, 15 pictures from the Hubble Space Telescope have been mosaicked to cover the inner 2.5 light years of the nebula and illustrate its diverse nature. In addition to housing a bright open cluster of stars known as the Trapezium, the Orion Nebula contains many stellar nurseries. These nurseries contain hydrogen gas, hot young stars, proplyds, and stellar jets spewing material at high speeds. Most of the filamentary structures visible in this image are actually shock waves - fronts where fast moving material encounters slow moving gas. Shocks are particularly apparent near the bright stars in the lower left of the picture. The Orion Nebula is about 1500 light years distant, located in the same spiral arm of our Galaxy as the Sun.
Normally, Earth based astronomers view Saturn's spectacular ring system fully illuminated by reflected sunlight. However, this November 1995 Hubble Space Telescope composite image was made to take advantage of an unusual perspective, with the Sun actually illuminating the rings from below. The three bright ring features are visible because the rings themselves are not solid. Composed of many separate chunks of rocky, icy material, the rings allow the scattered sunlight to pass through them -- offering a dramatic demonstration that they are not continuous, uninterrupted bands of material. | 0.94234 | 3.478553 |
Not too close, but not too far. That’s long been the rule describing how distant a planet should be from its star in order to sustain life. But a new study challenges that adage: A planet can maintain water and other liquids on its surface if it’s heated, not by starlight, but by radioactive decay, researchers calculate. That opens up the possibility for many planets—even free-floating worlds untethered to stars—to host life, they speculate.
Source: Science Magazine
Radioactive isotopes such as uranium-238, thorium-232, and potassium-40 pepper Earth’s crust and mantle. As these unstable radionuclides decay, they generate a small amount of power—roughly one-thirty-thousandth that received from the Sun. But researchers have now proposed that some planets, particularly ones that form near the center of our Milky Way Galaxy, might possess enough of these radioactive isotopes to generate sufficient heat to keep their surfaces from freezing entirely solid.
“That gives you the freedom to be anywhere,” says Avi Loeb, an astrophysicist at Harvard University and a co-author of the new study. “You don’t need to be close to a star.”
Loeb and Manasvi Lingam, an astrobiologist at the Florida Institute of Technology, looked at three sources of heat for a sunless planet: heat leftover from its formation, the radioactive decay of long-lived isotopes over billions of years, and the radioactive decay of short-lived isotopes over hundreds of thousands of years. They then modeled the surface temperatures of planets with different masses and radionuclide abundances to determine whether water, ammonia, and ethane—three solvents found in the Solar System—could exist as liquids.
Warming a planet enough to liquify water requires roughly 1000 times Earth’s abundance of both types of radioactive isotopes, Lingman and Loeb report in The Astrophysical Journal Letters. Lingam and Loeb found that planets with the same mass as Earth but with about 100 times the abundance of radionuclides would pump out enough heat to keep ethane liquid over hundreds of millions of years. The radiation levels on such worlds would be hundreds of times higher than the time-averaged doses Chernobyl residents experienced after the Ukrainian nuclear disaster in 1986, Lingam and Loeb estimated.
It’s unlikely that multicellular life would survive such irradiation, Lingam says. But some of Earth’s most extreme microbes would have better than a fighting chance. For instance, Deinococcus radiodurans, a highly radiation-resistant bacterium, would do just fine, Lingam says. “Deinococcus radiodurans is a really crazy organism.”
Could a single planet amass such a large stockpile of radionuclides? That’s the key question, Loeb says. Such worlds, if they existed in our own Galaxy, would probably have to be born near the center of the Milky Way. That’s because heavy elements such as uranium and thorium are thought to be produced in collisions between neutron stars, and such collisions are more likely to occur in the densely crowded center of the Galaxy.
But finding such a planet would come as a surprise because it’s so unlike the other worlds in our solar system, says Tim Lichtenberg, a planetary scientist at the University of Oxford who was not involved in the research. “It’s hard to argue that it’s impossible. But it’s definitely not the norm.”
If one of these worlds does exist, the James Webb Space Telescope, slated to launch in 2021, might be able to spot it by virtue of the radiation it would emit. But one of the telescope’s cameras would need roughly 10 days to detect the signal, which would be strongest in the infrared, Lingam and Loeb calculated. And that exposure estimate could vary wildly depending on the planet’s age, radionuclide abundance, and mass. “There are so many unknowns,” Lingam says. “We haven’t said the last word.”
Source: Science Magazine | 0.870737 | 3.838332 |
AuthorGibbard, Seran Gwen, 1967-
KeywordsPhysics, Astronomy and Astrophysics.
Physics, Electricity and Magnetism.
Physics, Atmospheric Science.
AdvisorLevy, Eugene H.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractLightning, a familiar phenomenon on Earth, may also occur at other times and locations in our solar system. It has been suggested as a mechanism for forming chondrules, millimeter-sized beads of glassy silicate found in primitive meteorites formed in the early solar system 4.5 billion years ago. It has also been detected in Voyager images of Jupiter, and there is evidence that it may occur on other planets as well, including Venus, Saturn and Neptune. The mechanism believed to produce lightning discharges on Earth, and possibly other planets, is charge production by collisions of ice particles, followed by gravitational separation of oppositely-charged large and small particles. This work examines the possibility of the occurrence of lightning discharges in the atmospheres of Jupiter and Neptune as well as in the protoplanetary nebula (PPN) of the early solar system by modeling charge separation and growth of the electric field. The model is also applied to the Earth as a test of its predictive power. It is found that the model can reproduce the correct timescale, particle charge and electric field magnitude seen in terrestrial lightning. The model also predicts lightning on Jupiter at the 3-5 bar level provided that the local water abundance is greater than the solar value. This is a much higher abundance than measured by the Galileo probe into Jupiter's atmosphere, which suggests that the water content measured by the probe does not apply to the entire planet. An application of the model to Neptune's water and NH₄SH clouds finds that lightning is unlikely in these clouds due to the large electric field required for electrical breakdown. Lightning may be possible in the overlying H₂S-NH₃ cloud provided that these substances can undergo collisional charge exchange with a magnitude at least 1% of that found in water ice. In the protoplanetary nebula, it appears that large-scale precipitation-induced lightning could not have occurred, due to the small mass density, low temperature and high electrical conductivity of the surroundings. This is a robust conclusion that does not depend sensitively on the values of the parameters involved.
Degree ProgramGraduate College | 0.887436 | 3.761512 |
Giant planets, terrestrial planets and major satellites
Dr HH Mate
Contd from prev issue
Mars : The mass of Mars is approximately one-tenth that of the Earth, and hence significant differences in the internal structure are to be expected. There appears to be less of a density contrast between the core of Mars and that of its mantle, suggesting that the amount of lighter material allied with the core-say, possibly sulphur-is increased relative to the Earth. Because the planet is smaller, the temperature increases less rapidly with depth than in the case of the Earth, and hence Mars should have a somewhat more rigid outer mantle and crust than the Earth.
There is no indication that large amounts of continental drift have taken place on Mars. On the other hand, tectonic activity has clearly played a large role in the history of Mars, since the planet can be roughly divided into a hemisphere which is of pre-dominantly ancient and heavily cratered terrain, and another hemisphere which is of much younger and less heavily cratered material. The density of craters on the surface of a planet such as Mars, with so little atmosphere that incoming massive bodies are not significantly impeded in striking the planet, is a measure of the relative age of the surface which has been exposed to space. Since the cratering rate apparently fell off rapidly throughout the first few hundred million years of the history of the inner solar system, differences in crater density frequently represent age differences of some few hundred million years back in the heavy cratering epoch.
Mercury : Mercury has only about half the mass of Mars, but has several distinct planetary characteristics. The mean density of Mercury is very high, indicating that Mercury probably has an abnormally large core predominantly composed of metallic iron. There is much evidence of extensive tectonic activity, although, like Mars, the increase of temperature below the surface of Mercury probably occurs sufficiently slowly so that the crust and upper mantle are relatively rigid, and nothing resembling continental drift has probably taken place.
Mercury is a very heavily cratered planet, with the craters of a given size apparently having been produced by smaller projectiles than in the case of Mars. The reason is that the distance of Mercury from the sun such incoming projectiles tend to have higher velocities than they do near the orbit of Mars, so that the resulting impacts are more energetic.
Moon : Although the Earth’s moon is technically a satellite, it makes sense to describe it as a planetary body, and planetary scientists consider the twin bodies of the Earth and the Moon as interesting examples of the extremes of planetary physics ranging from relatively large bodies to relatively small but still chemically differentiated objects.
The Moon has a history which includes extensive episodes of melting and differentiation, much of which can be reconstructed on the basis of the returned lunar samples. The upper layers of the Moon, which is just over 1% of the mass of the Earth, are quite rigid, and there is no evidence for extensive horizontal motions of the structural units.
The moon is unique in the solar system in having a relatively low density among the inner planets, and at best a very small core, indicating that the planet is practically devoid of metallic iron. Relative to the Earth it is also highly depleted in the more volatile elements. This unsual compositional pattern presumably requires an explanation in the mechanisms which resulted in the formation of the moon, about which there has been much controversy.
Major Satellites : The four Galilean satellites of Jupiter-Io, Europe, Ganymede, and Gallisto have masses which are all roughly comparable to the mass of the Earth’s Moon. It is, therefore, quite clear that they should be considered as planetary bodies in their own right by planetary scientists. The detailed images of these satellites returned by the Voyager space craft which passed through the Jupiter system revealed them to be very interesting places with many rich, complex, and exotic properties.
The most spectacular of these planetary bodies is undoubtedly Io. This satellite has a surface characterized by large deposits of sulphur and sulphur dioxide, which is in a state of continual change. It appears to have at any time several active volcanoes, each of which is likely to be spewing a stream of gas and entrained rocky particles about 60 miles or 100 kilometres or so above the surface.
Such volcanic plumes spread the gases and rocky materials from the volcano over a considerable portion of the surrounding terrain. This vigorous tectonic activity is understood to arise from a combination of orbital perturbations of Io by the other Galilean satellites and tidal damping by Jupiter, which results in the dissipation in the interior of Io of very large amount of heat. | 0.895673 | 3.888563 |
Radar images have shown that a near-Earth object is actually a triple system; an asteroid with two small moons. NASA’s Goldstone Solar System Radar on June 12 and 14, 2009, revealed the new informaton about Asteroid 1994 CC. It came within 2.52 million kilometers (1.56 million miles) on June 10. Prior to the flyby, very little was known about this celestial body. 1994 CC is only the second triple system known in the near-Earth population. A team led by Marina Brozovic and Lance Benner, both scientists at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., made the discovery.
1994 CC consists of a central object about 700 meters (2,300 feet) in diameter that has two smaller moons revolving around it. Preliminary analysis suggests that the two small satellites are at least 50 meters (164 feet) in diameter. Radar observations at Arecibo Observatory in Puerto Rico, led by the center’s director Mike Nolan, also detected all three objects, and the combined observations from Goldstone and Arecibo will be utilized by JPL scientists and their colleagues to study 1994 CC’s orbital and physical properties.
The next comparable Earth flyby for asteroid 1994 CC will occur in the year 2074 when the space rock trio flies past Earth at a distance of two-and-a-half million kilometers (1.6 million miles).
Of the hundreds of near-Earth asteroids observed by radar, only about 1 percent are triple systems. | 0.836415 | 3.211422 |
Al-Battani: Pioneering Muslim Mathematician-Astronomer Extraordinaire (Part-2)
Aristotle, Ptolemy and the other Greek masters might have been great theorists of science, but the patient work of direct observation and studied inference based on obtainable evidence was left to stand apart as the hallmark of the early Muslim scientists inspired by the Qur’anic revelation: a revelation that compelled its believers to observe and ponder over the creation of the universe and the world all around – and, indeed, within – them. Not only does al-Battani’s Kitāb az-Zīj give us the results of his observations and analysis, but his inferences also allow data given for one era to be converted to another era, writes BIJU ABDUL QADIR in this concluding part of the series on the life and achievements of one of the greatest astronomers of all time: the ninth century Muslim scientist, Abū ʿAbdAllāh Muḥammad ibn Jābir ibn Sinān al-Raqqī al-Ḥarrānī al-Ṣābiʾ al-Battānī.
Moving Past Ptolemy: Trigonometric Innovations over Greek Geometry
The strongest and most lasting influence of al-Battani’s investigations, perhaps, was his work with the ratios related to the sides and angles of right triangles – or to describe this discipline in one word: trigonometry. Al-Battani’s innovative use of the sine, tangent-cotangent functions, and his discovery and deployment of the secant and cosecant functions were, in fact, a vast improvement over the techniques employed by Ptolemy (c.127CE), the greatest of Greek astronomers. Some of al-Battani’s famous innovations in trigonometry led to equations such as the following:
Thus putting forward a number of important trigonometric functions, he wrote accurate tables for cotangents for angles from 0-900. He found the cotangents in his tables as represented by the following functions:
Cot x = Cos x/ Sin x
In his book, Mathematics History, Florian Cajori noted that:
“Al-Battani did not follow the Greek in many of their Geometry solutions; he instead solved problems by another way: [for e.g.,] m = Sin x/ Cos x. But,
Thus, the value x for the angle could be obtained.”
According to one Western source:
“Al-Battānī used al-Marwazi’s idea of tangents (‘shadows’) to develop equations for calculating tangents and cotangents, compiling tables of them. He also discovered the reciprocal functions of secant and cosecant, and produced the first table of cosecants, which he referred to as a ‘table of shadows’ (in reference to the shadow of a gnomon), for each degree from 1° to 90°.” [http://www.academia.edu/4652595/Al-Battani_Contributions_in_Astronomy_and_Mathematics]
However, staying true to the tradition of Arab astronomers of not belittling Ptolemy’s genius, al-Battani fought shy of openly critiquing the great Greek even when he was himself certain of Ptolemy’s several errors. Al-Battani sought, rather, to correct Ptolemy’s findings in a tacit manner without direct reference to any of the latter’s misjudgments. Carrying on the work of reform and updation in this honourable way, al-Battani soon compiled new tables of the sun and moon, correcting, in the process, some of Ptolemy’s results which were, for long, held as indisputable truths.
While Ptolemy had correctly surmised the direction of the Sun’s apogee, it was left to al-Battani to discover that this direction was actually changing. This change in direction is now known as occurring due to the changing direction of the eccentricity vector of the Earth’s orbit.
Based again on his observations, al-Battani also came to the conclusion that the longitude of the sun’s apogee had actually gone up by 16° 47′ since Ptolemy’s time. This, of course, led to the subsequent – and important – discovery of the motion of the solar apsides and of a slow variation in the equation of time. As mentioned earlier, al-Battani’s measurement of the length of the solar year was the most accurate up to that point in history; this was while Ptolemy’s own measurement of the same value had overstepped the correct value by 6 minutes and 26 seconds.
Staying true to his original streak in research, al-Battani preferred, even in the company of other astronomers of his time, to employ a uniform rate for precession in his tables, instead of adopting the theory of trepidation attributed to his learned contemporary, Thabit b. Qurra, and which Copernicus still held as viable centuries after both these Arab masters had passed away. In Encyclopedia Britannica, we read the following with regard to one in several of al-Battani’s propositions which have held their ground through the centuries:
“Al-Battani gave a rule for finding the elevation θ of the sun above the horizon in terms of the length s of the shadow cast by a vertical gnomon of height h. Al-Battani’s rule, s = h sin (900 – θ)/ sin θ, is equivalent to the formula s = h cot θ. Based on this rule, he constructed a ‘table of shadows’ – essentially a table of cotangents – for each degree from 10 to 900.” (www.britannica.com)
The Kitābaz-Zīj: Astronomy Encyclopedia of Generations
Al-Battani is known to have written several tracts on the subject of his astronomical studies, but few were as consequential and far-reaching in its legacy as his Magnum Opus, the Kitāb az-Zīj, or the Book of Astronomical Tables, sometimes also referred to as Az-Zīj as-Ṣābi’. It is known that some of his observations mentioned in the Kitāb az-Zīj were made in the year 880CE and, later on, in the year 900CE. Al-Battani put forth his first edition of this work before 900CE, but he then revised the same sometime after 901CE. This was so as to incorporate the results of his observation of two eclipses – a solar and a lunar eclipse – which he had the chance to see that same year while on a visit to Antioch in Syria.
While the influence of Ptolemy and of other Greco-Syriac sources is discernible at several places in this compendium of astronomical data, the book shows minimal, if any, Indian or Persian dependence. Publishing many of his observations and inferences in the Kitāb az-Zīj, al-Battani further enhanced the value of the work by extensively supporting it with tables. A curious interest in astrology is peculiar to al-Battani’s study inasmuch as his subjecting Ptolemy’s Tetrabiblos to rigorous scrutiny was combined with his own study on the signs of the Zodiac in the same work. Indeed, a whole chapter in the Kitāb az-Zīj is entitled: ‘On Ascensions of the Signs of the Zodiac.’ It is possible that the position of astrology, in the ancient world, as a relevant science, did not go without its effect on al-Battani, for there are quite a few of his shorter essays which sought to address different aspects of astrology. Moreover, seven chapters of the Kitāb az-Zīj are dedicated to a discussion of problems in astrology, rather than astronomy.
In all, Kitāb az-Zīj consists of 57 chapters, headed by a description of the celestial sphere which al-Battani divided into degrees. There is then an introduction to the requisite mathematical instruments like arithmetical operations on sexagesimal fractions as also trigonometric functions. Another chapter – the fourth – provides data from al-Battani’s own observations. No less than 21 chapters which follow on this fourth chapter are dedicated to the discussion of numerous problems in astronomy; to a certain extent, at least, al-Battani is seen here as having followed through with the content of Ptolemy’s Almagest.
The next five chapters of Kitāb az-Zīj offer a discussion of the motion of the sun, moon and five planets with some reference to Ptolemy’s theory. However, to al-Battani, the theory was after all just that – theory – and had little meaning unless, and until, supported by the practical aspects of direct observation and experience. This, in fact, represented the classic Arab-Muslim stance on all scientific matters: the preference for empirical observation over abstract, or even plausible, theorization. Aristotle, Ptolemy and the other Greek masters might have been great theorists of science, but the patient work of direct observation and studied inference based on obtainable evidence was left to stand apart as the hallmark of Muslim scientists inspired by the Qur’anic revelation: a revelation that compelled its believers to observe and ponder over the creation of the universe and the world all around – and, indeed, within – them.
Not only does al-Battani’s Kitāb az-Zīj give us the results of his observations and analysis, but his inferences also allow data given for one era to be converted to another era. In fact, he then puts forward sixteen chapters which explain how his tables are to be read and understood. The next seven chapters address problems in astrology, while the second last chapter – the 56th – is, in its entirety, dedicated to a discussion on the construction of a single instrument: the sundial. Moving further ahead on instruments, al-Battani ends his book with a final chapter which explains the construction of several other types of astronomical instruments.
In many ways, the Kitābaz-Zīj was a landmark accomplishment, not only for al-Battani personally, but also for the history of astronomy, mathematics and even instrumentation. Cataloging, within the pages of the Zij, the position of no less than 489 stars among other important findings, al-Battani also recorded for posterity, his refined value for the length of the solar year and of the seasons, the precession of the equinoxes as well as his accurately observed value for the inclination of the ecliptic. The Zijalso showed how, unlike Ptolemy, who worked with geometrical methods, al-Battani had employed trigonometrical techniques which ultimately proved an undeniable advance for astronomical and mathematical research. One among several important formulas for right-angled triangles, which was developed by al-Battani – and recorded in the Zij– is the following:
bSinθ = a Sin (90-θ)
The Kitāb az-Zīj Survives – Through a Fortunate Irony of History
In time, theZij came to be rendered into Latin twice in the twelfth century: once by Plato of Tivoli and then by Robert Retinensis, the latter translator probably being the same Robert of Chester who was the first scholar to produce a Latin translation of the Qur’an. However, only one of these two valuable translations survived: the one done by Plato of Tivoli in 1116CE, which came out under the title, De Motu Stellarum(‘On the Motion of the Stars’), with later annotations by Regiomontanus. There is, fortunately, one other translation of the Zijwhich has outlived the vicissitude of the ages: the Spanish version commissioned by King Alfonso X of Spain in the thirteenth century.
It is not without reason that the middle ages in Europe have often been called the ‘Dark Age.’ A period of religious diktats and persecution, several generations of Europeans were witness to this time of brutal repression by the Church which forbade any advance in science that put a question mark on Christian dogma in whatever form. Galileo Galilee and Nicolas Copernicus were themselves famous victims of this throttling of scientific endeavour by the Church authorities who often worked hand-in-glove with the State in matters of religious concern.
However, it is among the fortunate ironies of history, that even in this time of repression, when precious few books were authorized for publication in printed form, al-Battani’s Kitāb az-Zīj actually made it to the list of approved works. In 1537CE, the translation of the Zij by Plato of Tivoli was published from Nuremberg, Germany. Another edition of the same work then made its appearance in Bologna, Italy, in 1645CE. The Zij was thus fast becoming popular among the astronomers and mathematicians of central and northern Europe. Not only among Christian scientists, but even among astronomers of the Jewish community in Spain, was the Zij warmly received and to great acclaim, so much so that even as late as 1749CE, al-Battani’s observations of eclipses were still being referred to, and studied, by astronomers.
Closer to the modern period, it was during the years between 1899-1907CE that C. A. Nallino, the European historian of Islam, produced a large, three-volume, Arabic edition of the Kitāb az-Zīj. With the arrival of this new and substantial edition of the Zijat the turn of the last century, the book – and its author – has held the sustained attention of modern historians of science. Al-Battani is, today, well-respected within informed western academic circles as having been a keen follower – and reformer – of Ptolemaic theories of astronomy and as a vital connecting link between the astronomical sciences of the world of antiquity and those of the modern world.
The original manuscript of the Kitāb az-Zīj is, of late, maintained at the Vatican in Rome. Another valuable manuscript on astronomical chronology – also written by al-Battani – is known to be in the possession of the Escorial library.
Death and Legacy
As an astronomer, it is known that al-Battani remained active well into his 60th year (c.918CE). Another decade later, we find him again in 929CE, aged 71, but, nonetheless, accompanying a group of people from Raqqah on a journey to Baghdad. The apparent reason for the journey: to protest unfair taxes slapped on the populace by the government of the time. It has also been recorded that the aging, but determined, astronomer survived the onward journey, managing even to state his case before the authorities at Baghdad. Unfortunately, however, he did not survive the journey back to Raqqah. Al-Battani passed away at Qasr al-Jiss near what is today Samarrah in Iraq.
Nearly six decades after his death, al-Battani’s work was chronicled in the Fenrist compiled by the book-seller, Ibn Nadim. The Fehrist contained a useful list of Arabic literature (and the respective authors) extant then in the tenth century. About al-Battani, the Fehrist makes mention that he made his astronomical observations during the period between 877CE and 918CE, and that his star catalogue was from the year 880CE. Ibn an-Nadim was quite categorical in his praise for al-Battani whom he calls “one of the famous observers and a leader in geometry, theoretical and practical astronomy, and astrology.” Ibn an-Nadim further noted that:
“[al-Battani] composed a work on astronomy, with tables, containing his own observations of the sun and moon and a more accurate description of their motions than that given in Ptolemy’s Almagest. In it, moreover, he gives the motions of the five planets, with the improved observations he succeeded in making, as well as other necessary astronomical calculations. Some of his observations mentioned in his book of tables were made in the year 880 and later on in the year 900. Nobody is known in Islam who reached similar perfection in observing the stars and scrutinizing their motions. Apart from this, he took great interest in astrology, which led him to write on this subject too. Of his compositions in this field, I mention his commentary on Ptolemy’s Tetrabiblos.”
To be sure, Ibn an-Nadim’s comments on al-Battani’s life and achievements were not the exaggerations of a devout Muslim; they were, rather, an assertion of what was already known about this remarkable scientist throughout the Arab world of that time.
However, it was – and still is – the non-Arab, non-Muslim, Western world which, despite drawing on his pioneering scholarship centuries later for its own rebirth from its Dark Ages, remains generally and, perhaps, deliberately oblivious to the great legacy and civilizational contributions that al-Battani and other pioneering Muslim scientists, time and again, offered the world of men. | 0.872243 | 3.256119 |
Mars’ catastrophic geology
New information about Mars is highlighting the catastrophic nature of its past. Planetary geologists are finding a variety of indications of very rapid processes in Mars history. These processes often have some parallel on Earth but because Mars is much colder and has a very different atmosphere there are differences in the effects even for well known Earth-like processes.
Martian processes include flooding, volcanism, glacial movement, sedimentary processes and even geysers. NASA and the European Space Agency have gathered valuable data on Mars geology from recent missions that will give new insights into Mars history. How should young-age creationists understand this new information?
The Northern part of Mars is called the Northern Lowlands because it averages about 4–5 km lower in elevation than the Southern half of the planet. The Southern Highlands are very densely cratered but fewer craters are seen on the surface in the Northern Lowlands. On the other hand, the Northern Lowlands has many buried craters. In 2006, the European Space Agency’s Mars Express mission (also known as MARSIS) found evidence of what are apparently impact structures buried under the surface ranging from 130 to 470 km in diameter.1 This was using a special instrument known as a sounding radar. Mars is well known for many channels on its surface as well. Most of the channels formed as a result of subsidence phenomena, but there are often dendritic drainage patterns in or around them, indicating water drained into them or eroded in them after their formation.
Mars’ atmosphere is quite thin and if there were liquid water on the surface of Mars today it would quickly evaporate and/or freeze. Water and carbon dioxide ice exist on both the poles of Mars and water ice under the surface. Recently the Mars Odyssey spacecraft mapped patches of water ice just below the surface.2 Being a planet with a relatively low density (3.9 g/cm3 compared to 5.5 for Earth), Mars has the potential for having a lot of volatile material in its interior, such as water and carbon dioxide.
Evidence seems to have been discovered recently of water eruptions3 sometime in Mars’ past from two channels on Mars known as Mangala Fossa and Cerberus Fossa, described as graben fractures. Mangala Fossa seems to have had hot water carrying mud with it. Scientists have estimated 107 –108 m3/s for the water volume flux from Mangala Fossa from a fracture about 200 km long. Cerberus Fossa (fracture about 35 km long) seems to have been a carbonated water geyser with a volume flux of about 2 × 106 m3/s. Both of these eruptions propelled material several kilometres laterally across the surface. The nature of the channels and ridges produced by these eruptions seem to rule out volcanic flows. Cerberus Fossa is believed to have sent hailstones several kilometres. The force of these eruptions requires that the water come from aquifers as deep as 3–4 km below the surface.
These water eruptions are just one example of a variety of large-scale rapid catastrophic events that have shaped the surface of Mars in its past. There are also massive volcanoes and evidence of glaciation. A major ongoing mystery is how the Martian atmosphere could support so much liquid water in the past, as is indicated by all the evidence of water on the surface. There are sedimentary deposits of sulfate and clorite compounds (evaporites), as well as hematite. A mineral similar to granite was also found in limited quantities.4 This suggests a variety of processes that may involve water coming up from below the surface.
There is much yet to be thoroughly researched and examined on Mars from a young-age creation perspective. For example, was Mars created with a thicker atmosphere than present that was partially lost as a result of large impacts? It is very possible for the explosion of a large impact to blast gases away at greater than escape velocity, especially since Mars gravity is about 38% of Earth’s. An alternative might be powerful outgassing from the interior after creation (possibly driven by accelerated radioactive decay) that increased the density of the atmosphere at least temporarily. Then heating from the interior could have triggered a massive melting of glaciers and subsurface ice, causing much erosion of the surface from liquid water that flowed for some period of time. There’s obviously been massive lava flows on Mars as well. But, something has caused a melting or evaporation of water under the surface that led to water flows creating many surface channels. There may have also been large regions once glaciated on Mars that have been resurfaced by basalt and dust.
Whatever happened in Mars’ past, it was dramatic and catastrophic. Though this is all tentative at this point, Martian geology will generally demand rapid catastrophic processes and thus will fit a young-age viewpoint nicely.
- Watters, T.R., Leuschen, C.J., Plaut, J.J., Picardi, G., Safaeinili, A., Clifford, S.M., Farrell, W.M., Ivanov, A.B., Phillips, R.J. and Stofan, E.R., MARSIS radar sounder evidence of buried basins in the northern lowlands of Mars, Nature 444:905–908, December 14, 2006. Also available as a press release at <mars.jpl.nasa.gov/express/newsroom/pressreleases/20061213a.html>. Return to text.
- Sharp views show ground ice on Mars is patchy and variable, 3 May 2007, <themis.asu.edu/news-groundice>. Return to text.
- Shiga, D., Fizzy water powered ‘super’ geysers on ancient Mars, New Scientist News, 17 March 2008, <space.newscientist.com/channel/solar-system/dn13480-fizzy-water-powered-super-geysers-on-ancient-mars.html>. Return to text.
- Bandfield, J.L., Hamilton, V.E., Christensen, P.R. and McSween Jr, H.Y., Identification of quartzofeldspathic materials on Mars, J. Geophys. Res. 109:E10009, 2004. Or, see, Granite-like rocks discovered, <themis.asu.edu/discoveries-granitepeaks>. Return to text. | 0.876406 | 3.461135 |
Your daily selection of the latest science news!
According to Universe Today
For the sake of studying the most distant objects in the Universe, astronomers often rely on a technique known as Gravitational Lensing. Based on the principles of Einstein’s Theory of General Relativity, this technique involves relying on a large distribution of matter (such as a galaxy cluster or star) to magnify the light coming from a distant object, thereby making it appear brighter and larger.
However, in recent years, astronomers have found other uses for this technique as well. For instance, a team of scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) recently determined that Gravitational Lensing could also be used to determine the mass of white dwarf stars. This discovery could lead to a new era in astronomy where the mass of fainter objects can be determined.
The study which details their findings, titled “Predicting gravitational lensing by stellar remnants” appeared in the Monthly Noticed of the Royal Astronomical Society. The study was led by Alexander J. Harding of the CfA and included Rosanne Di Stefano, and Claire Baker (also from the CfA), as well as members from the University of Southampton, Georgia State University, the University of Nigeria, and Cornell University.
To put it simply, determining the mass of an astronomical object is one the greatest challenges for astronomers. Until now, the most successful method relied on binary systems because the orbital parameters of these systems depend on the masses of the two objects. Unfortunately, objects that are at the end states of stellar evolution – like black holes, neutron stars or white dwarfs – are often too faint or isolated to be detectable.
This is unfortunate, since these objects are responsible for a lot of dramatic astronomical events. These include the accretion of material, the emission of energetic radiation, gravitational waves, gamma-ray bursts, or supernovae. Many of these events are still a mystery to astronomers or the study of them is still in its infancy – i.e. gravitational waves. As they state in their study:
“Gravitational lensing provides an alternative approach to mass measurement. It has the advantage of only relying on the light from a background source, and can therefore be employed even for dark lenses. In fact, since light from the lens can interfere with the detection of lensing effects, compact objects are ideal lenses.”
As they go on to state, of the 18,000 lensing events that have been detected to date, roughly 10 to 15% are believed to have been caused by compact objects. However, scientists are unable to tell which of the detected events were due to compact lenses. For the sake of their study then, the team sought to circumvent this problem by identifying local compact objects and predicting when they might produce a lensing event so they could be studied.
“By focusing on pre-selected compact objects in the near vicinity of the Sun, we ensure that the lensing event will be caused by a white dwarf, neutron star, or black hole,” they state. “Furthermore, the distance and proper motion of the lens can be accurately measured prior to the event, or else afterwards. Armed with this information, the lensing light curve allows one to accurately measure the mass of the lens.”
In the end, the team determined that lensing events could be predicted from thousands of local objects. These include 250 neutron stars, 5 black holes, and roughly 35,000 white dwarfs. Neutron stars and black holes present a challenge since the known populations are too small and their proper motions and/or distances are not generally known.
But in the case of white dwarfs, the authors anticipate that they will provide for many lensing opportunities in the future. Based on the general motions of the white dwarfs across the sky, they obtained a statistical estimate that about 30-50 lensing events will take place per decade that could be spotted by the Hubble Space Telescope, the ESA’s Gaia mission, or NASA’s James Webb Space Telescope (JWST). As they state in their conclusions:
“We find that the detection of lensing events due to white dwarfs can certainly be observed during the next decade by both Gaia and HST. Photometric events will occur, but to detect them will require observations of the positions of hundreds to thousands of far-flung white dwarfs. As we learn the positions, distances to, and proper motions of larger numbers of white dwarfs through the completion of surveys such as Gaia and through ongoing and new wide-field surveys, the situation will continue to improve.”
The future of astronomy does indeed seem bright. Between improvements in technology, methodology, and the deployment of next-generation space and ground-based telescopes, there is no shortage of opportunities to see and learn more.
- Got any news, tips or want to contact us directly? Email [email protected] | 0.878563 | 3.836833 |
Dear Glutdawnous Readers,
The distant dwarf planet that Dawn is circling is full of mystery and yet growing ever more familiar.
Ceres, which only last year was hardly more than a fuzzy blob against the stars, is now a richly detailed world, and our portrait grows more elaborate every day. Having greatly surpassed all of its original objectives, the reliable explorer is gathering still more data from its unique vantage point. Everyone who hungers for new knowledge about the cosmos or for bold adventures far from Earth can share in the sumptuous feast Dawn has been serving.
One of the major objectives of the mission was to photograph 80 percent of Ceres' vast landscape with a resolution of 660 feet (200 meters) per pixel. That would provide 150 times the clarity of the powerful Hubble Space Telescope. Dawn has now photographed 99.8 percent with a resolution of 120 feet (35 meters) per pixel.
This example of Dawn's extraordinary productivity may appear to be the limit of what it could achieve. After all, the spaceship is orbiting at an altitude of only 240 miles (385 kilometers), closer to the ground than the International Space Station is to Earth, and it will never go lower for more pictures. But it is already doing more.
Since April 11, instead of photographing the scenery directly beneath it, Dawn has been aiming its camera to the left and forward as it orbits and Ceres rotates. By May 25, it will have mapped most of the globe from that angle. Then it will start all over once more, looking instead to the right and forward from May 27 through July 10. The different perspectives on the terrain make stereo views, which scientists can combine to bring out the full three dimensionality of the alien world. Dawn already accomplished this in its third mapping orbit from four times its current altitude, but now that it is seeing the sights from so much lower, the new topographical map will be even more accurate.
Dawn is also earning extra credit on its assignment to measure the energy of gamma rays and neutrons. We have discussed before how the gamma ray and neutron detector (GRaND) can reveal the atomic composition down to about a yard (meter) underground, and last month we saw initial findings about the distribution of hydrogen. However, Ceres' nuclear glow is very faint. Scientists already have three times as much GRaND data from this low altitude as they had required, and both spectrometers in the instrument will continue to collect data. In effect, Dawn is achieving a longer exposure, making its nuclear picture of Ceres brighter and sharper.
In December we explained how using the radio signal to track the probe's movements allows scientists to chart the gravity field and thereby learn about the interior of Ceres, revealing regions of higher and lower density. Once again, Dawn performed even better than expected and achieved the mission's planned accuracy in the third mapping orbit. Because the strength of the dwarf planet's gravitational tug depends on the distance, even finer measurements of how it varies from location to location are possible in this final orbit. Thanks to the continued smooth operation of the mission, scientists now have a gravitational map fully twice as accurate as they had anticipated. With additional measurements, they may be able to squeeze out a little more detail, perhaps improving it by another 20 percent before reaching the method's limit.
Dawn has dramatically overachieved in acquiring spectra at both visible and infrared wavelengths. We have previously delved into how these measurements reveal the minerals on the ground and what some of the interesting discoveries are. Having already acquired more than seven times as many visible spectra and 21 times as many infrared spectra as originally called for, the spacecraft is adding to its riches with additional measurements. We saw in January that VIR has such a narrow view that it will never see all of Ceres from this close, so it is programmed to observe features that have caught scientists' interest based on the broad coverage from higher altitudes.
Dawn's remarkable success at Ceres was not a foregone conclusion. Of course, the flight team has confronted the familiar challenges people encounter every day in the normal routine of piloting an ion-propelled spaceship on a multibillion-mile (multibillion-kilometer) interplanetary journey to orbit and explore two uncharted worlds. But the mission was further complicated by the loss of two of the spacecraft's four reaction wheels, as we have recounted before. (In full disclosure, the devices aren’t actually lost. We know precisely where they are. But given that one stopped functioning in 2010 and the other in 2012, they might as well be elsewhere in the universe; they don’t do Dawn any good.) Without three of these units to control its orientation in space, the robot has relied on its limited supply of hydrazine, which was not intended to serve this function. But the mission's careful stewardship of the precious propellant has continued to exceed even the optimistic predictions, allowing Dawn good prospects for carrying on its fruitful work. In an upcoming Dawn Journal, we will discuss how the last of the dwindling supply of hydrazine may be used for further discoveries.
In the meantime, Dawn is continuing its intensive campaign to reveal the dwarf planet's secrets, and as it does so, it is passing several milestones. The adventurer has now been held in Ceres' tender but firm gravitational embrace longer than it was in orbit around Vesta. (Dawn is the only spacecraft ever to orbit two extraterrestrial destinations, and its mission would have been impossible without ion propulsion.) The spacecraft provided us with about 31,000 pictures of Vesta, and it has now acquired the same number of Ceres.
For an interplanetary traveler, terrestrial days have little meaning. They are merely a memory of how long a faraway planet takes to turn on its axis. Dawn left that planet long ago, and as one of Earth's ambassadors to the cosmos, it is an inhabitant of deep space. But for those who keep track of its progress yet are still tied to Earth, on May 3 the journey will be pi thousand days long. (And for our nerdier friends and selves, it will be shortly after 6:47 p.m. PDT.)
By any measure, Dawn has already accomplished an extraordinary mission, and there is more to look forward to as its ambitious expedition continues.
Dawn is 240 miles (385 kilometers) from Ceres. It is also 3.73 AU (346 million miles, or 558 million kilometers) from Earth, or 1,455 times as far as the moon and 3.70 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and two minutes to make the round trip. | 0.870534 | 3.592744 |
A new study reveals that the Hellas impact basin on Mars once contained a number of ephemeral lakes, or lakes that are usually dry but fill up with water for brief periods of time.
Boniswa Khumalo PARIS — The crust that encases rocky planets and makes possible the emergence of life took shape on Mars earlier than thought and at least million years sooner than on Earth, researchers said on Wednesday.
Water is considered to be an essential precursor for life, at least as we know it. Mars was once much more Earth-like, with a thick atmosphere, abundant water and global oceans. Up to now, mathematical models have suggested that the solidification of the Red Planet took up to million years.
The new study tackles the question by examining a chunk of Mars that streaked into the Saharan Desert and was discovered in The Black Beauty meteorite weighed grams when found. The researchers secured 44 grammes of the precious space rock, and crushed five -- enough to extract seven bits of zircon that could be used in experiments.
Nasa plans to send mini-helicopter to Mars In one, it occurs in stages, with small dust particles coalescing into "planetesimals" -- rock fragments ten to kilometres in diameter -- that collide to form planetary embryos, and then planets, over a time scale of 50 to million years.
According to a more recent model, planetary growth unfolds more quickly and is fuelled by so-called "pebble accretion", the layered accumulation of particles measured in centimetres and metres that are loosely bound with gases.
So you want to go to Mars? Getting there is hard, but surviving on the Red Planet is harder. The new timeline suggests that something similar may have happened on our planet, but only after Earth was "reset" by the giant impact that formed the Moon about 4.
Mars is thought to have a dense metallic core with a radius of about 1, kilometres, consisting primarily of iron, nickel and sulphur. The core is surrounded by a largely dormant mantle -- some 1, km thick -- made mainly of silicon, oxygen, iron and magnesium.
Finally, the crust averages about 50 km in depth, with a maximum of about km.A new study about terraforming Mars finds that it's not possible to transform the planet into a more habitable place for humans using today's technology. e-news; To study quakes on Red Planet,NASA’s newest Mars lander. NASA's InSight lander aims to be the first to reach Mars since the Curiosity rover, pictured here on Mars' Vera Rubin Ridge, which landed in and remains on the planetNASA is poised to launch its first lander to Mars since , an unmanned spacecraft called InSight that aims to listen for quakes and unravel the mystery of.
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, and is often referred to as the " Red Planet " because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the Surface pressure: (–) kPa, atm.
Mars may have liquid water—a huge lake nestled under the ice cap at the planet’s southern pole, researchers report today (July 25) in Science. Planetary scientists have debated for decades whether the Red Planet has liquid water, usually discussing the possible presence of small amounts that.
The Mars Ice Home is a concept study for a potential astronaut habitat on Mars.
Take a look at this photo tour to see what it might be like to live on the Red Planet. Nov 05, · A new study, reveals that the Hellas impact basin on Mars once contained a number of ephemeral lakes, or lakes that are usually dry but fill up with water for brief periods of time. | 0.861395 | 3.509526 |
It’s been a rather supermassive year for black holes. These enigmatic monsters finally showed face in April, with the first ever image of a black hole making its way down to Earth. Using the Event Horizon Telescope, astronomers finally gave the world physical evidence of the existence of black holes. Located in galaxy M87, the black hole revealed its shining, red hot glory with a mass 6.5 billion times larger than the sun.
As scientists gain access to more powerful telescopes and advanced technologies that lead to these kinds of revelations, they answer old questions and formulate new ones.
Through these new observations, scientists have learned one thing for certain: Black holes can act pretty weird sometimes. And in commemoration of black hole week, we’re recapping some of the wackiest, most bizarre behavior observed this year, including hungry black holes, black holes that have tricked stars into orbiting around them, and just about everything in between.
Joe Pesce, Ph.D., program director at the National Science Foundation’s Division of Astronomical Sciences, explains how greater clarity has lead to unprecedented and often puzzling observations in the past couple of years.
“We opened a new realm of observations,” Pesce tells Inverse. “We also have many more questions because we’re seeing things we’ve never seen before.”
So without further ado, here are the 7 weirdest black hole finds of recent years:
7. Our galaxy’s black hole might be getting hungrier
We’re starting off with a black hole that’s not too far from home, located only 26,000 light-years away in the center of the Milky Way. On May 13, astronomers observed the area around the black hole to be twice as bright as the brightest it had ever been before.
The sudden burst of light indicated that an unusually large amount of interstellar gas and dust hd fallen into the center of the black hole and was consumed by it, giving our galaxy’s black hole the unflattering reputation that it was getting hungrier.
However, further observations are needed to determine whether this was a one-off occurrence or if in fact the black hole located in the center of the Milky Way is developing a bigger appetite for cosmic matter.
6. A really, really supermassive black hole
We already know supermassive black holes are big, but in August, astronomers who use the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile spotted its largest one yet. Located around 100 million light-years away from Earth at the center of galaxy NGC 3258, a supermassive black hole measured at 2.25 billion times the mass of our sun.
“We’re not sure how black holes get that mass, how they get that big,” Pesce says.
Scientists are still unsure exactly how these large black holes form, but reaching this size can take less than a billion years.
5. The cloaked black hole of the early universe
One of the rarest sightings of black holes, this mysterious cloaked monster appeared behind a cloud of gas to a team of astronomers using the Chandra X-Ray Observatory. The black hole was reportedly born less than a billion years after the universe began, making it nearly 13 billion years old.
During their early growth period, black holes are usually cloaked behind a dense cloud of gas, which forms as the black hole consumes surrounding matter for much needed nurture.
This gas cloud makes it harder to detect these adolescents, therefore the sighting of a cloaked black hole is quite the treat for astronomers as it helps them better understand the evolution of black holes.
4. Tiny black hole in dwarf galaxy vs. tiny galaxy with pretty big black hole
A black holes are typically envisioned as burning bright, massive beings at the center of colossal galaxies. But two back-to-back observations this year showed that black holes come in all sizes, and so do their host galaxies.
Scientists measured a black hole in a nearby dwarf galaxy that turned out to be 40 times smaller than they had originally anticipated — only 10,000 times the mass of our sun. It is widely believed that galaxies the size of the Milky Way or larger have a supermassive black hole at their center, but little is known about the black holes of smaller galaxies — and whether black holes necessarily exist in each of them.
A second observation added even more mystery: A dwarf galaxy was hosting a supermassive black hole in its tiny center. For a long time, astronomers believed that size does matter for galaxies — the bigger the galaxy, the bigger the black hole. But this unusual pairing, a galaxy that is 3 percent the size of the Milky Way and a black hole that measures at over a million times the mass of our sun, defies all previous perceptions.
3. Cosmic material wobbles around this black hole
Astronomers observing a black hole in a nearby galaxy, nearly 8,000 light-years from Earth, saw something quite strange. Fast-moving, hot jets of stellar material were shooting out of the area surrounding the black hole, and those jets were wobbling and changing direction in a matter of minutes.
Using the National Science Foundation’s Very Long Baseline Array, the team of astronomers observed the black hole consuming material from a nearby star. That material formed a dense disk of material around the black hole that kept getting hotter as it was drawn closer to the center of the black hole. But the black hole’s gravitational pull was so strong, that it was tugging at its surrounding space.
According to the General Theory of Relativity, massive objects like black holes can distort space and time around them. And since the black hole’s axis was misaligned with the plane of its companion star’s orbit, the black hole tugged at space-time and created its signature wobble.
2. A black hole with a strict meal plan
If there’s one thing we’ve learned about black holes so far, it’s that they’re pretty erratic. But not this black hole, located around 250 million light-years away, which was eating three meals a day. That’s a regular schedule, even on a human timescale.
Every 9 hours, this black hole would consume a pretty large meal — around a million billion billion pounds of stellar material or the equivalent of about four moons.
A team of scientists first noticed this odd behavior through a series of X-ray bursts that were 20 times brighter than usual coming from Galaxy GSN 069.
1. This starving black hole is hungry no more
On the other hand, black holes in low luminosity galaxies are believed to be “starving” black holes because their host galaxy lacks a strong enough gravitational pull to provide cosmic material for the black hole to munch on.
However, the black hole at the center of spiral galaxy NGC 3147, around 130 million light-years away, was observed with a thin disk of material circling around it similar to disks observed in heftier galaxies.
Scientists had originally picked to observe this galaxy in order to confirm their theories about starving black holes, only to find it with a healthy spread of food.
It turns out this black hole was not skipping its meals after all. | 0.827275 | 3.758275 |
The scientific community was abuzz earlier this year when it was revealed that, despite Pluto’s demotion, the Solar System may have a hidden ninth planet after all, hanging out in the far reaches of the distant, frigid Kuiper Belt. Based on the perturbed orbits of massive rocky and icy bodies drifting way beyond the orbit of Neptune, it has yet to be directly imaged, but evidence for its existence, according to some astronomers, is fairly strong.
Now, a new piece of research uploaded to the arXiv pre-print server suggests something even more remarkable is happening beyond our current line of sight. If Planet Nine is actually there, it’s unlikely it could have survived in our Solar System on such a stable orbit for 4.5 billion years without some planetary accomplices. In short, there may be a Planet Ten and Eleven, and possibly more, in the shadows, whose orbits are stabilizing each other’s.
“Planet Nine, if it exists, moves in an elongated orbit that may be vulnerable to long-term perturbations. In this context, a lone Planet Nine may not be able to survive in its present orbit for the age of the Solar System,” the researchers write in their study. “A planet within a planetary group has better chances to be long-term stable. Therefore, if Planet Nine exists, it is probably not alone.”
The team came to this striking conclusion using the same types of numerical models that were first used by astronomers to conclude that our Solar System does indeed contain a concealed planet. Without these extra buffering planets, close encounters with other stars may otherwise pull it away from our own Sun.
This new study, led by astronomer Carlos de la Fuente Marcos of the Complutense University of Madrid, also concludes that several large objects near Planet Nine – including Sedna, a dwarf planet that’s only slightly smaller than Pluto – will be able to remain in their own orbits for many millions of years to come.
However, a few others – such as 2004 VN112, another dwarf planet – are already in such eccentric, elliptical orbits that their interaction with Planet Nine will eventually cause them to be ejected from the Solar System and into the deep, dark reaches of space.
Gif in text: Planet Nine’s hypothetical orbit compared to known orbital paths within the Solar System. nagualdesign/Wikimedia Commons; CC BY 3.0
The interactions of massive objects, whether they are moons, planets, asteroids, stars or even black holes, are highly complex, and cause a variety of effects. Sometimes, if they’re too close to each other, they can collide and destroy each other, which explains where, among other things, Saturn’s rings came from.
Conversely, as highlighted in this mathematical study, planets on a very eccentric and unstable orbit can be perturbed by other nearby, similarly sized planets. Planet Nine’s hypothetical trajectory around the Sun is somewhat eccentric, and the team’s models suggest that without being pulled around a bit by other similarly sized worlds nearby, it would have left the Solar System by now.
The orbital parameters of Planet Nine in 3D. caltech via YouTube
Speaking of interactions between massive objects, one recent study suggested that if Planet Nine is real, it could have been captured by our own Sun from another star system as our local star left its stellar nursery at the start of its life. This may explain why its orbit is fairly eccentric in the first place.
Like another study that claims Planet Nine is likely to be part-Neptune, part-Earth in terms of its geology, this is all just speculation – albeit rigorously scientific in nature – until Planet Nine is directly detected. The hunt is on, as they say. | 0.85709 | 3.837665 |
In early 2016, two planetary scientists declared that a ghost planet is hiding in the depths of the solar system, well beyond the orbit of Pluto. Their claim, which they made based on the curious orbits of distant icy worlds, quickly sparked a race to find this so-called Planet Nine—a planet that is estimated to be about 10 times the mass of Earth. “It has a real magnetism to it,” said Gregory Laughlin, an astronomer at Yale University. “I mean, finding a 10-Earth-mass planet in our own solar system would be a discovery of unrivaled scientific magnitude.”
Now, astronomers are reporting that they have spotted another distant world—perhaps as large as a dwarf planet—whose orbit is so odd that it is likely to have been shepherded by Planet Nine. The object confirms a specific prediction made by Konstantin Batygin and Michael Brown, the astronomers at the California Institute of Technology who first argued for Planet Nine’s existence. “It’s not proof that Planet Nine exists,” said David Gerdes, an astronomer at the University of Michigan and a co-author on the new paper. “But I would say the presence of an object like this in our solar system bolsters the case for Planet Nine.”
Gerdes and his colleagues spotted the new object in data from the Dark Energy Survey, a project that probes the acceleration in the expansion of the universe by surveying a region well above the plane of the solar system. This makes it an unlikely tool for finding objects inside the solar system, since they mostly orbit within the plane. But that is exactly what makes the new object unique: Its orbit is tilted 54 degrees with respect to the plane of the solar system. It’s something Gerdes did not expect to see. Batygin and Brown, however, predicted it.
Two years ago, Batygin and Brown made a case for Planet Nine’s existence based on the peculiar orbits of a handful of distant worlds known as Kuiper belt objects. That small population loops outward toward the same quadrant of the solar system, a phenomenon that would be extremely unlikely to happen by chance. Batygin and Brown argued that a ninth planet must be shepherding those worlds into their strange orbits.
What’s more, Batygin and Brown also predicted that over time, Planet Nine’s gravity would push these Kuiper belt objects out of their current plane and into ever-higher orbital inclinations. Although astronomers have already spotted a bizarre population of worlds that orbit the sun perpendicularly to the plane of the solar system, they had never caught an object transitioning between the two populations. “There’s no real way to put something on an orbit like that—except that it’s exactly what we predicted from Planet Nine,” Brown said. Batygin notes that the new object fits so perfectly with their model that it almost looks like one of the data points in their simulations. “A good theory reproduces data—but a great theory predicts new data,” he said.
The Dark Energy Survey first detected evidence for the new object in late 2014. Gerdes and his colleagues have spent the years since then tracking its orbit and trying to understand its origins. In the new paper, they describe how they ran many simulations of the object within the known solar system, letting the clock run forward and backward 4.5 billion years at a time. Nothing could explain how the object landed in such a tilted orbit. It wasn’t until they added in a ninth planet—a planet with characteristics that perfectly match Batygin and Brown’s predictions—that the wacky orbit finally made sense. “The second you put Planet Nine in the simulations, not only can you form objects like this object, but you absolutely do,” said Juliette Becker, a graduate student at Michigan and the lead author on the new paper. A strong and sustained interaction with Planet Nine appears to be the only way to pump up the object’s inclination, pushing it away from the plane of the solar system. “There is no other reasonable way to populate the Kuiper belt with such highly inclined bodies,” Batygin said. “I think the case for the existence of Planet Nine is now genuinely excellent.”
Other astronomers aren’t so certain—in part because the early solar system remains a mystery. Scientists suspect that the sun was born within a cluster of stars, meaning that the early planets might have had many close encounters with other stars that sent them on paths that seem impossible today. And even once the stars dispersed, the early solar system likely contained tens of thousands of dwarf planets that could have provided the gravitational nudges needed to push 2015 BP519, as the new object is called, into such an odd orbit. “To me, Planet Nine is one of a number of ways that the solar system could have unfolded,” said Michele Bannister, an astronomer at Queen’s University Belfast who was not involved in the study. “It’s a potential idea.” But at the moment it is just that—an idea.
Yet when astronomers examine the larger universe, the idea doesn’t seem all that surprising. Planets between two and 10 times the mass of Earth are incredibly common throughout the galaxy, which makes it odd that our solar system doesn’t harbor one. “If it wasn’t in our own solar system—if the stakes weren’t so high—I think that the hypothesis would almost certainly be correct,” Laughlin said. “It’s only the fact that it’s so amazing that tends to give me pause.” Finding a ninth planet within our solar system would be both transformative and extraordinarily inspiring, he said. “It would be this dramatic confirmation of the scientific method, which would be pretty refreshing in the current age where the truth is on trial.”
Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences. | 0.848065 | 3.911697 |
Speed of the Milky Way in Space As we all know, a galaxy is a massive ensemble of hundreds of millions of stars. The galaxy where we live in today is called the Milky Way. The name itself came from the ancient Greek galaxies kyklos, or ring of milk, due to its faint milky appearance. Our Milky Way is a large spiral galaxy. Ever since four hundred years ago the settlement that the Earth is moving about the sun, and one hundred and fifty years ago that the sun is moving about the center of the Galaxy, it shouldn't be surprising if we learned that the Galaxy is also moving. In 1928, an American astronomer Milton La Salle Humason found a galaxy that was receding at a speed of 3,800 km/s, and by 1936, when he observed the same galaxy again, he found it receding at a speed of 40,000 km/s. If our galaxy exerted a repulsive force, that force should be felt with the local groups, however it wasn't. In conclusion, galaxies experience neutral attractions on one other. Patricia Kong -- 1999 Burstein, David.
Java Generics FAQs - Frequently Asked Questions All text and content found at URLs starting with (collectively, "the Java Generics FAQ") are the sole property of Angelika Langer. Copyright @ 2004-2019 by Angelika Langer . All rights reserved. Except as specifically granted below, you may not modify, copy, publish, sell, display, transmit (in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise), adapt, distribute, store in a retrieval system, create derivative works, or in any other way use or exploit the contents of the Java Generics FAQ, without the prior consent of the author. All rights, titles and interest, including copyrights and other applicable intellectual property rights, in any of the material belongs to the provider of the material. You do not acquire proprietary interest in such materials by accessing them on my web site. In particular, I do NOT grant permission to copy the Java Generics FAQ or any part of it to a public Web server.
Laboratory Equipment Neutron star Neutron stars contain 500,000 times the mass of the Earth in a sphere with a diameter no larger than that of Brooklyn, United States A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Neutron stars are the densest and tiniest stars known to exist in the universe; although having only the diameter of about 10 km (6 mi), they may have a mass of several times that of the Sun. Neutron stars probably appear white to the naked eye. Neutron stars are the end points of stars whose inert core's mass after nuclear burning is greater than the Chandrasekhar limit for white dwarfs, but whose mass is not great enough to overcome the neutron degeneracy pressure to become black holes. The discovery of pulsars in 1967 suggested that neutron stars exist. Neutron star collision Formation Properties Gravitational light deflection at a neutron star. Given current values Structure
What Is a Black Hole? An artist's drawing a black hole named Cygnus X-1. It formed when a large star caved in. This black hole pulls matter from blue star beside it. A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. Because no light can get out, people can't see black holes. How Big Are Black Holes? Another kind of black hole is called "stellar." An artist's drawing shows the current view of the Milky Way galaxy. The largest black holes are called "supermassive." How Do Black Holes Form? Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. Scientists think supermassive black holes were made at the same time as the galaxy they are in. This image of the center of the Milky Way galaxy was taken by the Chandra X-ray Observatory. Image Credit: NASA/CXC/MIT/F.K. If Black Holes Are "Black," How Do Scientists Know They Are There? Image Credit:
How fast is our galaxy moving through space "The Milky Way and the Andromeda galaxy are approaching each other with a speed of 300,000 miles per hour." or 130 km/s As we all know, a galaxy is a massive ensemble of hundreds of millions of stars. Ever since four hundred years ago the settlement that the Earth is moving about the sun, and one hundred and fifty years ago that the sun is moving about the center of the Galaxy, it shouldn't be surprising if we learned that the Galaxy is also moving. In 1928, an American astronomer Milton La Salle Humason found a galaxy that was receding at a speed of 3,800 km/s, and by 1936, when he observed the same galaxy again, he found it receding at a speed of 40,000 km/s. If our galaxy exerted a repulsive force, that force should be felt with the local groups, however it wasn't. In conclusion, galaxies experience neutral attractions on one other.
Multi-Agent Transport Simulation | MATSim Optics, Lasers, Imaging & Fiber Information Resource Neutron Stars - Introduction Neutron stars are compact objects that are created in the cores of massive stars during supernova explosions. The core of the star collapses, and crushes together every proton with a corresponding electron turning each electron-proton pair into a neutron. The neutrons, however, can often stop the collapse and remain as a neutron star. Neutron stars are fascinating objects because they are the most dense objects known. Like their less massive counterparts, white dwarfs, the heavier a neutron star gets the smaller it gets. Neutron stars can be observed occasionally, as with Puppis A above, as an extremely small and hot star within a supernova remnant.
Black hole A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater. Objects whose gravity fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. History General relativity
NASA finds extra-terrestrial amino-acids in Sudan meteorites Earlier this month, NASA announced the discovery of bacteria living in arsenic in a California lake. Now they have uncovered ET amino-acids in meteorite fragments that landed in northern Sudan. The meteorite was a fragment of a parent asteroid measuring 13-feet-wide (4m), and weighing 59-tons. Read more... Amino-acids have been found in carbon-rich meteorites before but this is the first time the acid substances have been found in a meteorite as hot as 2,000 Fahrenheit (1,100c). | 0.801591 | 3.044845 |
Unexplained deep space mysteries. The universe contains some much stranger, much larger, and much more terrifying mysteries than you ever thought to be afraid of.
The Travelling Blackhole
Black holes are bad news, but here’s one way to make them worse: send them flying across space. That’s apparently what happened to one particularly large black hole, and scientists can’t quite figure out why.
In 2012, NASA discovered what, in all likelihood, was a humongous black hole being kicked out of its galaxy. It was observed hurtling away at speeds of “several million miles per hour.” That a black hole got chucked like an unruly bar patron is bizarre enough, but consider just how massive a black hole is.
As astronomer Francesca Civano, who led the study that discovered the black hole, explained, this black hole is millions of times more massive than the Sun, and this galaxy just sent it packing like nothing. That’s like lifting an elephant with your pinkie and flinging it into the next state.
Supernovas are some of the largest explosions humans are ever likely to witness, and like most loud bangs, it doesn’t take too many before we start getting used to them. That is, until an even larger bang happens — then you sit up and take notice. That is the case with ASASSN-15lh, a superluminous supernova first observed in June 2015, that originated 2.8 billion light years away (and thus, 2.8 billion years ago!).
What makes ASASSN-15lh special is that scientists can’t explain it. Unlike a regular supernova, ASASSN-15lh was ten times brighter, and considerably more powerful. Also, when astronomers analysed the light it was emitting, they couldn’t find evidence of the hydrogen that should have been present.
The best explanation involves something called a magnetar—a kind of magnetic neutron star—that by rapidly spinning with a powerful magnetic field, could provide extra energy to the expanding ball of superheated gas. However, it didn’t take long for ASASSN-15lh to emit more energy than a magnetar should have been able to provide, and it just kept on going. Months after it first bloomed, it was still giving off more energy than the entire Milky Way galaxy we reside in.
But the strange didn’t stop there. The usual behavior for a supernova consists of a bright flash, followed by a slow fading. And while ASASSN-15lh initially followed this course, a few months after it started to fade, the ultraviolet light started to increase again. This is not entirely unknown behavior for supernovas, but the light being emitted didn’t fit the usual pattern. Scientists are still at a loss to fully explain the biggest bang known to mankind since the first one, and that’s pretty scary.
A popular way to look for planets these days is to measure the amount of light a star is giving off. When a planet passes in front of its host star, it will cause a small, but detectable, drop in brightness. And by measuring the frequency of these dips, plus the size, it’s possible to determine much about the nature of the planet, like if it is potentially habitable and thus home to alien life. Sometimes, however, the telescopes doing the observing see things that are harder to explain.
KIC 8462852 is a star in the Cygnus constellation approximately 1400 light years away from Earth. Unlike a star with a planet in orbit, this star displayed brightness dips of up to 20 percent, and they definitely weren’t regular. One explanation was a cloud of comet fragments that found their way into a tight orbit around the star, but another theory proposes something a lot more concerning.
In 1998, the Hubble telescope discovered that the universe was expanding much faster than it was before. Since then, NASA and friends have been trying to figure out why, and they still don’t really know. They’ve got theories, like what NASA dubbed “some strange kind of energy-fluid that filled space.” While such “energy-fluid” hasn’t been proven or disproven, they’ve still dubbed whatever it is “dark energy,” like a couple naming their kid years before making one.
So what is “dark energy”? We don’t really know. Really, all we know for sure is that there’s a lot more of it than light energy. NASA estimates the universe is about 68 percent dark energy, or roughly the amount Darth Vader had when he started questioning his loyalty to the Emperor. Dark energy’s cousin, the almost-as-mysterious “dark matter,” makes up an additional 27 percent of the universe. The remaining 5 percent is “light” energy, or stuff we can actually see. Yes: 95 percent of the universe is invisible. Sleep tight!
Gamma-ray bursts (GRBs) don’t happen very often, and considering they’re basically giant, super-long explosions of energy (the most recent one, 2013’s GRB 130427A, lasted 20 hours), that’s a good thing. However, their rarity means we don’t know too much about them, even though one may wind up killing us all some day.
We don’t know exactly what GRBs are or how they happen. As NASA explains, GRBs might be caused by low-energy gamma rays that, once exposed to space, explode into high-energy rays. But even NASA admits that’s just a theory, as are any other idea beyond “the Horrendous Space Kablooie come to life.” And they are horrendous indeed — a 2014 study showed frequent GRB explosions have left swaths of the universe completely inhospitable. That study also said there’s a good chance a GRB caused at least one mass-extinction event in Earth’s history. And while we probably won’t have a follow-up GRB (according to the BBC, our area isn’t really vulnerable to one), it’s still possible. The more we know about these things, the easier it might become to detect them before they explode and kill everything in sight. But that knowledge may be a long way off. | 0.876818 | 3.961785 |
The South Pole is an inhospitable place to do science. Temperatures can drop below minus 99 degrees Fahrenheit. The air is thin and moisture-less.
Yet physicists are flocking to an observatory there because it’s one of the best places to answer a mystery that’s been haunting their field for more than a century: What in the universe is shooting incredibly powerful beams of subatomic particles at Earth?
Scientists discovered in 1912 that subatomic particles — the building blocks of matter, such as protons, electrons, muons, neutrinos, and quarks — hit the Earth every day. They later learned they were hitting us with an energy that surpasses the power of human-built particle accelerators, like the Large Hadron Collider. Some of these particles carry so much energy that scientists have been puzzled as to which objects in space are powerful enough to create them.
Now, we have an important clue as to at least one object that may be responsible for some of these particles, often called “cosmic rays,” that hit the Earth. In two new studies appearing Thursday in Science, a large team of physicists reports that one of the sources of cosmic rays is a special type of galaxy called a blazar. Blazars have supermassive black holes at the center of them that rip apart matter into its constituent parts, and then blast subatomic particles off like a laser cannon into space.
The entire mystery of the source of cosmic rays is not solved. Scientists don’t know if there are other objects that can produce the rays, and the current results can’t yet explain the most powerful cosmic rays detected on record. They’re also not perfectly confident that the blazar is the source. (Physicists don’t use the word “certain” lightly.)
But it’s an intriguing start. Cosmic rays were first discovered in 1912. And we’re just now getting a big break to understand how they get here.
(The National Science Foundation is live streaming their press conference announcing the findings. You can watch that here.)
How a giant ice cube at the South Pole led to this discovery
There are some sources of cosmic rays that we do know about, like the sun, which is constantly spitting out bits of matter in all direction. Some cosmic rays can even be produced from atomic collision at the top of our atmosphere.
But then there are the cosmic rays being shot at us at energy levels that truly leave scientists dumbfounded. That’s the 100-year-old mystery.
The best comparison we have to explain the energy of these rays is the Large Hadron Collider near Geneva, Switzerland. The LHC is the most powerful, sophisticated particle accelerator on the planet. It can accelerate a proton to nearly the speed of light, and charge it with the energy of seven terra-electron-volts, or TEV. This is enough power to smash atoms into tiny, tiny pieces and reveal the architecture that makes up our universe.
It’s impressive. But it has nothing on the energy of the particles that rain down from space. The highest-energy cosmic ray particle ever recorded, called the “Oh-My-God” particle, was two million (!) times more energetic than the protons propelled at the LHC.
“How does nature do this?” Francis Halzen, a University of Wisconsin particle physicist and a lead collaborator on the new discovery, asks. “This has been for decades listed as one of the big open questions in astronomy and physics.”
The problem with looking for the sources of these very high energy cosmic rays is that they don’t always travel in a straight line. And that means they can’t trace it back to its source. In fact, we have the Northern and Southern Lights near the poles because the Earth’s magnetic field redirects much of the cosmic rays to these regions.
This is where the South Pole observatory comes in. There, Halzen; Naoko Kurahashi Neilson, a particle physicist at Drexel University; and several of their colleagues in physics have been looking for answers in the ice.
They work on the IceCube Neutrino Observatory, which is built directly into the ice beneath the surface of the South Pole. The observatory is funded by the National Science Foundation and is operated by the University of Wisconsin.
Basically it is a 1-cubic kilometer (about 1.3 billion cubic yards) block of crystal-clear ice surrounded by sensors. These sensors are set up to detect when subatomic particles called neutrinos — which travel along with other subatomic particles in cosmic rays — crash into the Earth.
Neutrinos are different from the other components of cosmic rays in one hugely important way: They don’t interact with other forms of matter much at all. They don’t have any electrical charge so Earth’s magnetism doesn’t deflect them. And they travel through the universe in a relatively straight line, and we can trace them back to a source.
“If I shine a flashlight through a wall, the light won’t go through,” Neilson, a co-collaborator on both of the new papers in Science, explains. “That’s because the light particles, the photons, interact with the particles in the wall and they can’t penetrate. If I had a neutrino flashlight, that stream of neutrinos would go through the wall.”
But every once in a while a neutrino — perhaps every one in 100,000 — will hit an atom in the ice at the observatory and break the atom apart.
And then something spectacular happens: The collision produces other subatomic particles, like muons, which are then propelled to a speed faster than the speed of light as they pass through the ice.
You might have heard that nothing can travel faster than light. That’s true, but only in a vacuum. The photons that make up light (a subatomic particle in their own right) actually slow down a bit when they enter a dense substance like ice. But other subatomic particles, like muons and electrons, do not slow down.
When particles are moving faster than light through a medium like ice, they glow. It’s called Cherenkov radiation. And the phenomenon is similar to that of a sonic boom. (When you go faster than the speed of sound, you produce a blast of noise.) When particles move faster than light, they leave wakes of an eerie blue light like a speedboat leaves wakes in the water.
Here’s an artist’s depiction of what this all looks like. The neutrino is the tear-drop shape in gray.
It’s an exciting finding in the “multi-messenger” age of astronomy
The light emitted from the particles is why ice is critical to the observatory. It’s crystal clear. Sensors can spot the flashes and then draw a path to where it originated in the sky. The particular neutrino — and it was just one — that led to the new discovery hit the ice cube in September 2017 with an energy of 290 terra electron-volts. Again, that’s 40 times as energetic as the particles in the LHC.
Within a minute, the computers at the observatory determined the neutrino had come from the direction of the constellation Orion, and sent out an automated alert to observatories around the world to hunt for a more precise source.
Here, the researchers caught a lucky break. Almost simultaneously, the Fermi Gamma-ray Space Telescope detected an increase in energetic activity from a galaxy in the same direction. And observatories around the world and in space picked up on it too.
The Science papers argue this likely was not a coincidence: Fermi and the other observatories picked up the same blast of cosmic rays that propelled the neutrino to the IceCube observatory and they traced it to a single blazar 4 billion light-years away. Still, the scientists are not entirely sure.
“This result doesn’t make it absolutely certain the neutrino came from the blazar,” says Kyle Cranmer, an NYU particle physicist not involved in the research. “I’d want to see another such observation.”
And the IceCube scientists agree. “I compare it to a police investigation of a murder,” Halzen says. “We just made a breakthrough and we know we’re going to find the person, but [we] didn’t get him yet.” Though the case for the blazar is made more compelling by the fact that when the IceCube team went back through their data from the past few years, they found other neutrinos that were likely spat out by the same blazar.
IceCube detects neutrinos on a regular basis, and astronomers look at blazars on a regular basis. What’s new and exciting here is that the IceCube team was able to turn to colleagues in observatories around the world to track a high-energy neutrino to its source for the first time.
As with many discoveries in physics, this one raises more questions than it answers. Scientists still don’t know how blazars actually accelerate particles to such high energies. They don’t know if all blazars are capable of doing this, or just some of them. And they don’t know what other objects in the universe could produce high-energy cosmic rays.
“This is science as usual,” Halzen says. “You solve a problem, and then it opens many more questions that are harder to solve. But that’s a perfect situation to be in to make progress.”
But perhaps more exciting than these findings is that there’s likely much more to come from these kinds of international collaborations in astronomy. “Regardless of whether or not this neutrino is actually from this blazar or not, [the results they produced are] just an incredible exercising the muscles of the whole system,” says Sarah Demers, a Yale particle physicist not involved in the research. That the IceCube lab can send out an alert that other telescopes can corroborate in the same day is an impressive accomplishment.
In recent years, astronomers have become excited by the idea of “multi-messenger” astronomy — the idea of seeing the universe with forces of nature other than light. Yes, we can see the universe in all sorts of wavelengths of electromagnetic radiation: visible light, infrared, ultraviolet, gamma, and so on. But all of these forms of radiation are different forms of light. What’s new and exciting about physics today is that we can also “see” the universe in terms of neutrinos, and, as of two years ago, gravitational waves.
Combining the power of observatories that can probe electromagnetic radiation, neutrinos, and even gravitational waves make it easier to for scientists to peer further back into the universe. “That’s the game-changer here,” Neilson says. | 0.878021 | 3.797201 |
Clumps of material have adhered to the legs of the Phoenix Mars Lander, and the clumps continue to change and grow. The science team has discussed various possible explanations for these clumps. One suggestion is that they may have started from a splash of mud if Phoenix’s descent engines melted icy soil during the landing. Another is that specks of salt may have landed on the strut and began attracting atmospheric moisture that freezes and accumulates. The clumps are concentrated on the north side of the strut, usually in the shade, so their accumulation could be a consequence of the fact that condensation favors colder surfaces. Below, compare images taken on September 1, 2008, or the 97th Martian Day or sol, since landing with another image taken about three months earlier, on Sol 8.
Phoenix’s Robotic Arm Camera took both images. The top image from Sol 97 was taken at about 4 a.m. local solar time. The view in this Sol 97 image is southward. Illumination is from the early morning sun above the northeastern horizon. This is quite different from the illumination in the Sol 8 image, bottom which was taken in mid-afternoon.
The two images also show a contrast in the flat, smooth patch of exposed ice underneath the lander. Phoenix team members believe the ice was exposed from the spacecraft’s thrusters as it landed. In the latest image, the patches of ice exposed underneath the lander seem to be partly covered by darker material left behind as ice vaporizes away. The flat patch in the center of the image has the informal name “Holy Cow,” based on researchers’ reaction when they saw the initial image of it.
Source: Phoenix Gallery | 0.817599 | 3.118751 |
From: Royal Astronomical Society
Posted: Monday, April 20, 2009
An international team of scientists has found some of the most primitive matter containing abundant interstellar material analyzed to date amongst dust particles collected from the upper atmosphere by NASA aircraft. The samples were gathered in April 2003 during the Earth's passage through the dust stream left behind by comet 26P/Grigg-Skjellerup. Dr. Henner Busemann of the University of Manchester will present the results at the European Week of Astronomy and Space Science at the University of Hertfordshire on Tuesday 21st April.
"We found an extraordinary wealth of primitive chemical "fingerprints", including abundant pre-solar grains, true stardust that has formed around other earlier stars, some during supernova explosions, associated with extremely pristine organic matter that must pre-date the formation of our planets," said Dr. Busemann.
The interplanetary dust particles, which are only a few thousands of a millimeter in diameter, were analyzed by an international collaboration from the UK, the US and Germany. Two grains appear to have percentage levels of material thought to match the nebula from which the Solar System formed. One dust particle contained four pre-solar silicate grains with an unusual chemical composition that matches predictions for silicates formed from cooling gas following a supernova explosion. One of these grains, a fragment of olivine, was found next to a hollow, globule of carbon, most likely of interstellar origin. Organic coatings are suspected to be the time-capsules that protected and secured the survival of some of these fragile stellar silicate grains in the radiating space environment.
"These tiny grains combine all the most primitive features, found to date only separately in various meteorites, samples from the Stardust mission and interplanetary dust particles. The particular collection scenario allows us speculate that we truly have samples of a known source, comet Grigg-Skjellerup, in our hands," said Dr. Busemann.
The group compared their findings with Deep Impact observations of comet 9P/Tempel 1 and analyzes of samples from comet 81P/Wild 2 collected by Stardust. The comparison revealed surprising differences between the comets, which are all short-period comets with orbits constrained by Jupiter's gravitational field. Comet 81P/Wild 2 was found to have incorporated much higher levels of material formed in the inner Solar System, however all the comets contained materials such as carbonates that commonly indicate the presence of water.
The primitive matter, containing unaltered samples of the building blocks of our Solar System, gives insights into the turbulent processes leading to the formation of our Solar System and also the fate of comets orbiting since their formation at the outer edges of our planetary system. While the planets in the inner solar system, such as Earth or Mars, once experienced harsh conditions and have changed substantially over the past 4.5 billion years, comets are believed to store the original material of the early Solar System, acting as 'supersized refrigerators'.
"We still have much to learn from samples of primitive matter containing large amounts of interstellar grains. Aircraft offer a less costly way to collect cometary dust, albeit of unknown origin. Predictions and timed collection campaigns in the future offer an increased likelihood to analyze material from known comets without actually going there," added Dr. Busemann.
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After observing a part of the sky near the Southern Constellation of Ara for about two months using MeerKAT, a radio telescope based in the Karoo desert in South Africa, our team of scientists noticed something strange. The radio emission of an object brightened by a factor of three over roughly three weeks.
Intrigued, we continued watching the object and followed this up with observations from other telescopes. We discovered that the unusual flare came from a binary star system two stars orbiting each other in our own galaxy. The finding, published in the Monthly Notices of the Royal Astronomical Society, has, however, turned out to be very difficult to explain.
This is MeerKAT's first discovery of a ransient source an object that is not constant, either undergoing a significant change in brightness or coming in and out of view altogether. Given the catchy name MKT J170456.2-482100, it was found in the first field observed with the telescope, which means it is likely to be the tip of an iceberg of transients waiting to be discovered.
To understand our discovery, we started by matching our source with the position of a star, called TYC 8332-2529-1, about 1,800 light years from Earth. Because this star is relativity bright, we anticipated that a number of different optical telescopes detecting visible light rather than radio waves would have observed this star in the past.
Luckily, this turned out to be the case, allowing us to use such data to find out more about the star. It is a giant about two and a half times the mass of the Sun. Some of the optical telescopes, including ASAS, KELT and ASAS-SN, provided us with over 18 years of observations of the star. These helped us discover that the brightness of the star changes over a period of 21 days. We think this is because the star has large spots on it, just like sunspots.
We used the SALT telescope to obtain optical spectra of the star similar to using a prism to split white light into its constituent wavelengths. This can be used to determine the chemical elements present in the star, as well as the presence of a magnetic field. What's more, they enable scientists to tell if a star is moving, as movement causes these spectral lines to shift (Doppler shift).
The spectra revealed that the star has a magnetic field, and that it orbits a companion star every 21 days. However, we can only see a very faint, possible signature of the companion star in our observations so far. This tells us that the companion must be much fainter than the giant star. We also found, however, that the companion is likely to have at least 1.5 times the mass of the Sun.
So what could the companion be? A white dwarf (a cold, dead star) may seem likely, as they are often part of binary star systems like this. However, most white dwarfs have a smaller mass than the companion we spotted with a maximum mass of 1.6 times the mass of the Sun. So it is unlikely to be such a star.
The plot thickens
The radio flare itself could be caused by magnetic activity of the giant star, similar to solar flares but much brighter and more energetic. However, such flares are usually observed on dwarf stars rather than giant stars.
Known star systems involving a giant star and a Sun-like star could explain the findings with the magnetic activity of the giant star giving rise to flares. However, this doesn't fit, as there is no sign in the spectra that the binary companion is actually a Sun-like star.
Ben Stappers, principal investigator of MeerTRAP, one of the teams working on the project, said that because the properties of the system don't easily fit into our current knowledge of binary or flaring stars, it may represent an entirely new source class. We suspect that this might be some sort of exotic system that we have never seen before involving a radio-flaring giant star orbiting a neutron star (the dense remnant of a supernova star explosion) or a black hole.
MeerKAT is going to continue observing this source every week for the next four years, with the ASAS-SN optical telescope continuing to observe the giant star. This means we will be able to explore the physics and nature of this source and its flares for many years to come.
This will tell us about the dynamics of this system, how flares occur and ultimately help us investigate how it formed. As MeerKAT continues to search the sky, we hope that this is the first of many new and unusual sources waiting to be discovered.
Source: The Conversation Media Group Ltd | 0.866423 | 4.038829 |
Laboratory's solar system legacy
When the first humans stepped onto the moon a half-century ago on July 20, 1969, they knew they were venturing into the unknown. Some had feared their lander would be swallowed up by bottomless layers of dust as almost nothing was known about the moon surface at the time. But they knew it wouldn't, thanks in large part to groundbreaking research being performed at the University of Arizona's then fledging Lunar and Planetary Laboratory.
When Gerard P. Kuiper founded the laboratory nine years earlier, in 1960, there was skepticism and a lack of interest in humans visiting the moon. But reaching the moon became a priority as the space race ramped up in the early '60s. Kuiper and his UA laboratory were suddenly in demand.
Now, on the 50th anniversary of the first manned mission to the moon marked by the Apollo 11 landing, UA scientists celebrate the pioneering and pivotal role the UA has held in the explosion of space science research, helping to shape what we know about our solar system and beyond today.
"The UA has been a part of nearly every NASA planetary exploration mission, and with leadership roles on many of them," said Tim Swindle, director of the UA Department of Planetary Sciences and the Lunar and Planetary Laboratory, or LPL. "Our graduates and alumni have also been involved in many missions. That is our goal."
William K. Hartmann, a UA alumnus who studied with Kuiper, was instrumental in helping to create some of the first maps of the moon.
"We projected photos of the moon onto a white globe, then photographed the globe from different angles to make an atlas of lunar features from overhead, as they would be seen by astronauts orbiting the moon," Harmann said.
He also shaped early theories around the origins of Earth's moon and has made other significant contributions to the field of lunar science.
Over the course of his scientific career, Hartmann discovered several impact basins on the moon. During the 1960s, he predicted the age of the lunar lava plains. His predictions were confirmed through samples returned by the Apollo missions.
The Apollo missions also influenced Kuiper while at the UA. He took his students on field trips to places on Earth that he felt were representative of what students might see on the moon or in the solar system, such as Meteor Crater in northern Arizona, dune fields or the extensive lava flows blanketing the Big Island of Hawaii. Those types of instructive field trips continue today.
"During our field trips, students visit planetary analog sites," Swindle said. "It's an important part of our department culture. We can send a robotic spacecraft to places in our solar system and beyond, but we'll never be able to see them as well as we can see places on Earth. By comparing those sites using every scientific technique we can think of, we can learn what those places out there in space might be like."
In preparation for the Phoenix Mars mission, the first planetary mission led by a university, a UA team traveled to Antarctica to study how the instruments they had developed would work in what is considered the most Mars-like environment on Earth.
The LPL's legacy of studying places on Earth to understand places far, far away becomes more relevant as more powerful telescopes have begun discovering a growing list of planets orbiting other stars as well as stranger objects within our solar system, such as the asteroid Bennu.
Instruments onboard OSIRIS-REx, a UA-led sample-return mission, are currently imaging and mapping Bennu's surface. Planetary scientist and UA professor Erik Asphaug took courses at the UA in both astronomy and geoscience and is currently analyzing OSIRIS-REx images to understand the physics of Bennu's rocky surface in microgravity and its composition.
In September 2023, OSIRIS-REx will return with pristine samples scooped from Bennu. The samples will be studied to learn more about the earliest history of the solar system, much like the lunar rocks returned from the Apollo missions.
"Kuiper started with the right attitude and what was an unusual approach at the time—namely turning astronomical objects into places," Swindle said. "His guiding idea was to not just obtain higher and higher resolution images, but also figure out what those images mean and what those objects would look like if you were standing there. And that is really what we have been doing here at LPL ever since." | 0.87954 | 3.417089 |
The Planetary Society has a new improved guide to all the places we've landed—or crashed—on Mars, plus planned locations for the upcoming Perseverance, Tianwen-1, and Rosalind Franklin rover missions.
Our weekly newsletter is your toolkit to learn more about space, share information with your friends and family, and take direct action to support exploration. View past issues at planetary.org/downlink and sign up to receive The Downlink in your email at planetary.org/connect.
New observations reported this week in the journal Nature have cast doubt on the theory that thick deposits of ground ice lie conveniently close to the surface in permanently shadowed crater floors at the lunar poles.
Recent radar observations of Saturn’s moon Titan have produced the first direct evidence that the second largest moon in the solar system may be hiding pools of liquid hydrocarbons underneath its smoggy atmosphere.
SETI@home and BOINC are gradually converging, and the benefits for both are substantial. While SETI@home enjoys the increased flexibility of the BOINC platform, it brings to BOINC something of inestimable value to a distributed computing project: millions of SETI@home users, willing to use their computers' processing power for the advancement of scientific research.
SETI@home chief scientist Dan Werthimer and his team went back to Arecibo to reobserve the most promising candidate signals detected by the project so far. Unlike most of the year, when SETI@home piggy-backs on the regular operations of the telescope, this time the Werthimer's crew had the full use of the resources of the giant dish.
Scientists working on the European Space Agency's (ESA's) Mars Express detailed the mission's ambitious plan to study Mars from the top of its atmosphere to several kilometers beneath its surface, at a press conference in London, England last week.
SETI@home's Stellar Countdown has come to an end at the Arecibo Radio Observatory. All in all the Stellar countdown observed 227 promising locations in the sky. Within the next few weeks all the data collected and recorded will be processed by SETI@home users around to world.
After getting bumped off the telescope last week to make way for Solar flare observations, SETI@home Chief Scientist Dan Werthimer and his crew will spend 14 hours today observing the locations of SETI@home's most promising candidate signals, as well as a few other interesting locations. | 0.899679 | 3.332762 |
Image: A shadowy selfie taken 280 million km from Earth
On 21 September 2018, 280 million km from Earth, a roughly 1.5 square-metre cube descended towards a primitive space rock. After years of planning and 4 years in flight, this tiny spacecraft captured this 'shadow selfie' as it closed in on asteroid Ryugu, just 80 metres from the remnant of our Solar System's formation, 4.6 billion years ago.
The Hayabusa2 spacecraft is operated by the Japanese Space Agency (JAXA), supported in part by ESA's Estrack Malargüe deep-space tracking station. The spacecraft carries four small landers that will investigate the asteroid's surface, all four designed to gently fall onto the surface of the rocky boulder, taking advantage of its low gravity environment.
Around the time this remarkable picture was taken, the spacecraft released its two MINERVA-II1 rovers which have since successfully landed and demonstrated an ability to hop around this rock-strewn body.
"I cannot find words to express how happy I am that we were able to realize mobile exploration on the surface of an asteroid" enthused Yuichi Tsuda, Hayabusa2 Project Project Manager, "I am proud that Hayabusa2 was able to contribute to the creation of this technology for a new method of space exploration by surface movement on small bodies."
The next stage will see the Mobile Asteroid Surface Scout (MASCOT) lander released onto the asteroid's surface. Developed by the German Aerospace Center (DLR) in cooperation with the French Space Agency (CNES) MASCOT has enough power for a 12-hour mission, in which it will analyse the asteroid's surface at two different sites.
The Hayabusa2 spacecraft itself will collect three samples from Ryugu, bringing them back to Earth in December 2020. These strange specimens will provide insights into the composition of this carbonaceous asteroid—a type of space rock expected to preserve some of the most pristine materials in the Solar System.
As well as hopefully shining light on the origin and evolution of the inner planets, and the sources of water and organic compounds on Earth, this knowledge should help in efforts to protect our planet from marauding masses that come too close for comfort to our home planet.
Understanding the composition and characteristics of near-Earth objects is vital to defending ourselves from them, if one were to head in our direction. ESA's proposed Hera mission to test asteroid deflection is an ambitious example of how we can get to know these ancient bodies better, all in the name of planetary defence. | 0.835607 | 3.66008 |
In a picture taken by the Hubble Space Telescope, a jet of matter can be clearly seen ejected from the centre of a galaxy. The jet is 4,400 light-year long.
The fact that the jet hardly disperses over such a long distance suggests that it is highly charge. A strong magnetic field is required to keep something like this together over such a long distance, and the most likely source of that magnetic field is the jet itself.
Charged gases such as these are generally referred to as electric plasma. Their behaviours are different from electrical neutral gases. For one thing, they can keep together for enormous distances without dispersing.
Donald Scott, a contributor to the Thundrerbolt Project, has a very insightful lecture on this topic, worth looking up on the web for those interested in more information on this. In the same lecture, he discusses the mechanisms behind planetary formations. | 0.879779 | 3.040086 |
My question is, are mainstream cosmologists using “dark matter” and “dark energy” to prop up inherent problems of the big bang model of the universe’s origin?
I understand that some people take issue with inflationary big bang models, but to say that dark matter and dark energy were invented without any scientific justification (i.e., invoking the Tooth Fairy) paints a distorted picture. Although much about dark matter and dark energy remains to be discovered, both stand on a strong evidential basis.
The concept of dark matter readily flows from observations of our galaxy (and many others) and a straightforward application of Newtonian gravity. Measurement of an object’s orbit uniquely determines the amount of mass inside that orbit.1 For decades, astronomers have measured the orbits of Milky Way stars and stars in other galaxies. They used this information to determine the amount of mass in each respective galaxy. They have also added up all the mass from stars emitting detectable light (any form of electromagnetic radiation) for those galaxies. In every instance, astronomers find that the mass needed to explain the orbits exceeds the mass of the visible stars. Astronomers refer to the difference between required mass and visible mass as dark matter (you can charge scientists with a lack of creativity in naming things). Using a similar process, scientists find abundant evidence for dark matter in the vicinity of the Sun as well as in gigantic clusters of galaxies.
Strong evidence also supports the existence dark energy, which was discovered more recently than dark matter. One interesting measurement—independent of the methods that discovered dark energy in the first place—pertains to the large-scale structure of the universe (or how galaxies are clustered together).
Obviously, scientists don’t have a complete and final understanding of the cosmos. Thus, room for alternative models exists, even models without dark matter or dark energy. However, those competing models must explain the current evidence at least as well as inflationary big-bang models do, and right now non-big-bang models fail to meet that standard. | 0.844843 | 3.823373 |
What will the first image of a Black Hole and its event horizon look like? What will scientists imagine we find in galaxy M87 and what will their imaging algorithms suggest is observed.
If no photographs of Black Holes have been taken before how can astronomers now create images of them?
How do we make a picture from the sparse data collected by the EHT?
The Event Horizon Telescope (EHT) collects light from the black hole using a small number of telescopes distributed around the Earth. Once the EHT has measured data from the black hole, we still need to make a picture from it - a process referred to as imaging. The light we collect gives us some indication of the structure of the black hole. However, since we are only collecting light at a few telescope locations, we are still missing some information about the black hole’s image. The imaging algorithms we develop fill in the gaps of data we are missing in order to reconstruct a picture of the black hole.
Since there is a lot of missing data, you may ask how making a picture is even possible.
Imaging a Black Hole | Event Horizon Telescope
What is actually in reality and in nature there? It will be relatively bright, a plasmoid? Not black, not holes.
But there is one point I want to draw your attention to: there is always some ambiguity in what the true image is. Similarly, for the EHT, the data we take only tells us only a piece of the story, as there are an infinite number of possible images that are perfectly consistent with the data we measure. But not all images are created equal— some look more like what we think of as images than others. To chose the best image, we essentially take all of the infinite images that explain our telescope measurements, and rank them by how reasonable they look. We then choose the image (or set of images) that looks most reasonable.
Using these algorithms we are able to reconstruct pictures from the very sparse measurements measured with the EHT.
What you are looking at, what astronomy think they are observing, really does depend on your point of view. Scientists will say it is the event horizon and the environment of the Black Holes. That you can never directly photograph a BH itself.
Plasma Cosmology and Electric Universe theory suggests that it is not a Black Hole as they do not exist. BH's are just theories and mathematical models.
PC and EU may interpret these Black Hole figures as plasma z-pinches of monstrous Birkeland filaments, or at least very energetic plasmoids in galactic electromagnetic plasma circuits.
BBC documentary on How to See a Black Hole
The project combines radio observatories and telescope facilities from around the world to make up a virtual telescope with a diameter spanning the entire planet. This mega-telescope’s ultimate mission is to capture the first image ever of a black hole.
Although the concept of black holes has been long assumed to be fact, the Event Horizon Telescope’s success would definitively prove the existence of this scientific phenomena for the first time – and provide clear visual evidence.
How to See a Black Hole: The Universe's Greatest Mystery
Update 10 April 2019: Black Hole image released
The image matches what theoretical physicists and indeed, Hollywood directors, imagined black holes would look like, according to Dr Ziri Younsi, of University College London - who is part of the collaboration.
"It is remarkable that the image we observe is so similar to that which we obtain from our theoretical calculations. So far, it looks like Einstein is correct once again."
First ever black hole image released
This is similar to the Black Hole mergers where algorithms were used to filter out data and then select the results that resembled what they expected to find. Although those gravity waves were actually far beyond what they had predicted or theory said could happen.
"Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well," remarks Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory. "This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass."
Astronomers Capture First Image of a Black Hole | Event Horizon Telescope
Electromagnetic plasma, plasma torus, plasmoid?
The image shows an intensely bright "ring of fire", as Prof Falcke describes it, surrounding a perfectly circular dark hole. The bright halo is caused by superheated gas falling into the hole. The light is brighter than all the billions of other stars in the galaxy combined - which is why it can be seen at such distance from Earth.
The edge of the dark circle at the centre is the point at which the gas enters the black hole, which is an object that has such a large gravitational pull, not even light can escape.
First ever black hole image released
She started making the algorithm three years ago while she was a graduate student at the Massachusetts Institute of Technology (MIT).
She spearheaded a testing process whereby multiple algorithms with "different assumptions built into them" attempted to recover a photo from the data. Put simply, Dr Bouman and others developed a series of algorithms that converted telescopic data into the historic photo shared by the world's media.
In mathematics and computer science, an algorithm is a process or set of rules used to solve problems. The results of the algorithms were then analysed by four separate teams to build confidence in the veracity of their findings.
Katie Bouman: How did her algorithm create the image? | BBC | 0.855869 | 3.971415 |
The Wilkinson Microwave Anisotropy Probe (WMAP) was a NASA Explorer mission that made fundamental measurements of cosmology—the study of the properties of our universe as a whole.
The structure of the universe evolved from the Big Bang, as represented by WMAP’s “baby picture” of the Cosmic Microwave Background (the afterglow of the Big Bang), through the clumping and ignition of matter, and continuing up to the present. This video condenses that almost 14 billion year history into 45 seconds.
Video Credit: NASA
Astronomers have uncovered seven primitive galaxies that formed more than 13 billion years ago, when the universe was less than 4 percent of its present age. The deepest images to date from the Hubble Space Telescope show the first statistically significant sample that gives us an idea of how abundant galaxies were in the era when they were first forming.
The newly discovered galaxies are seen as they looked 380 to 600 million years after the big bang. Astronomers study the distant universe in near-infrared light because the expansion of space stretches ultraviolet and visible light from galaxies into infrared wavelengths, a phenomenon called redshift. The farther away a galaxy, the greater its redshift. One of these galaxies may be a distance record breaker, observed 380 million years after the big bang, corresponding to a redshift of 11.9.
The hot stars in the first galaxies provided radiation to warm the cold hydrogen that formed soon after the big bang. That made the universe transparent to light, allowing us to look far back into time. The galaxies in the new study are seen in this early epoch. Data shows that this was a gradual process, occurring over several hundred million years, with galaxies slowly building up their stars and chemical elements.
Image Credit: NASA | 0.863977 | 3.797702 |
Update 18 April 2018: After a two-day delay, NASA’s Transiting Exoplanet Survey Satellite (TESS) launched aboard a Falcon 9 rocket from Cape Canaveral, Florida. Now, operators will use the satellite’s onboard boosters to push it into its final orbit before beginning its observations of distant worlds. NASA plans to operate TESS until at least 2020.
Update 16 April 2018: The scheduled 16 April launch of the TESS satellite has been delayed. A tweet from SpaceX, which operates the Falcon 9 rocket set to take the satellite to space, indicated that delays were required to conduct analysis of the rocket’s guidance, navigation and control system. The new targeted launch date is 18 April.
Standing down today to conduct additional GNC analysis, and teams are now working towards a targeted launch of @NASA_TESS on Wednesday, April 18.
— SpaceX (@SpaceX) April 16, 2018
Original article, published 13 April 2018
NASA’s next exoplanet-hunting telescope is preparing for launch. The Transiting Exoplanet Survey Satellite (TESS), is scheduled to blast off aboard a Falcon 9 rocket on 16 April.
TESS is taking up the mantle of the Kepler Space Telescope, which is expected to run out of fuel by the end of this year. Kepler has found more than 5000 exoplanet candidates so far, and confirmed about half of them. TESS will be able to search 350 times more area of the sky than Kepler can, and is expected to find about 20,000 exoplanets in its first two years alone.
It will take about two months after launch to manouevre the satellite into its orbit – about half as far from Earth as the moon – and test its cameras. “After that, there’ll just be a flood of information,” says the mission’s principal investigator, George Ricker at the Massachusetts Institute of Technology.
Eyes on the sky
TESS will use the same transit method Kepler used to find planets. This involves watching a star for dips in its light as a planet passes between the star and the telescope. How often the dips repeat indicates how fast the planet circles its host star, and the amount of light that’s blocked tells us the size of the distant world.
Rather than looking at distant stars in a small area of sky, like Kepler did, TESS will look at closer stars over 85 per cent of the sky. It is optimised to observe smaller, cooler stars that emit mostly red light.
“90 per cent of the stars in the Milky Way emit in those red wavelengths, and they seem to have more planets than stars like the sun, especially smaller Earth-sized planets,” says Ricker. “Nature’s really saying, ‘look here, look here’ and that’s exactly what we’re going to do.”
Because those stars are so nearby and rich with planets, they will be ideal targets for the James Webb Space Telescope (JWST), due to launch in 2020. JWST will examine exoplanet atmospheres for signatures of life, which is only possible when their stars are relatively close.
More on these topics: | 0.829562 | 3.176536 |
Welcome all to the first in our series on Exoplanet-hunting methods. Today we begin with the most popular and widely-used, known as the Transit Method (aka. Transit Photometry).
For centuries, astronomers have speculated about the existence of planets beyond our Solar System. After all, with between 100 and 400 billion stars in the Milky Way Galaxy alone, it seemed unlikely that ours was the only one to have a system of planets. But it has only been within the past few decades that astronomers have confirmed the existence of extra-solar planets (aka. exoplanets).
Astronomers use various methods to confirm the existence of exoplanets, most of which are indirect in nature. Of these, the most widely-used and effective to date has been Transit Photometry, a method that measures the light curve of distant stars for periodic dips in brightness. These are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.
These changes in brightness are characterized by very small dips and for fixed periods of time, usually in the vicinity of 1/10,000th of the star’s overall brightness and only for a matter of hours. These changes are also periodic, causing the same dips in brightness each time and for the same amount of time. Based on the extent to which stars dim, astronomers are also able to obtain vital information about exoplanets.
For all of these reasons, Transit Photometry is considered a very robust and reliable method of exoplanet detection. Of the 3,526 extra-solar planets that have been confirmed to date, the transit method has accounted for 2,771 discoveries – which is more than all the other methods combined.
One of the greatest advantages of Transit Photometry is the way it can provide accurate constraints on the size of detected planets. Obviously, this is based on the extent to which a star’s light curve changes as a result of a transit. Whereas a small planet will cause a subtle change in brightness, a larger planet will cause a more noticeable change.
When combined with the Radial Velocity method (which can determine the planet’s mass) one can determine the density of the planet. From this, astronomers are able to assess a planet’s physical structure and composition – i.e. determining if it is a gas giant or rocky planet. The planets that have been studied using both of these methods are by far the best-characterized of all known exoplanets.
In addition to revealing the diameter of planets, Transit Photometry can allow for a planet’s atmosphere to be investigated through spectroscopy. As light from the star passes through the planet’s atmosphere, the resulting spectra can be analyzed to determine what elements are present, thus providing clues as to the chemical composition of the atmosphere.
Last, but not least, the transit method can also reveal things about a planet’s temperature and radiation based on secondary eclipses (when the planet passes behind it’s sun). On this occasion, astronomers measure the star’s photometric intensity and then subtract it from measurements of the star’s intensity before the secondary eclipse. This allows for measurements of the planet’s temperature and can even determine the presence of clouds formations in the planet’s atmosphere.
Transit Photometry also suffers from a few major drawbacks. For one, planetary transits are observable only when the planet’s orbit happens to be perfectly aligned with the astronomers’ line of sight. The probability of a planet’s orbit coinciding with an observer’s vantage point is equivalent to the ratio of the diameter of the star to the diameter of the orbit.
Only about 10% of planets with short orbital periods experience such an alignment, and this decreases for planets with longer orbital periods. As a result, this method cannot guarantee that a particular star being observed does indeed host any planets. For this reason, the transit method is most effective when surveying thousands or hundreds of thousands of stars at a time.
It also suffers from a substantial rate of false positives; in some cases, as high as 40% in single-planet systems (based on a 2012 study of the Kepler mission). This necessitates that follow-up observations be conducted, often relying on another method. However, the rate of false positives drops off for stars where multiple candidates have been detected.
While transits can reveal much about a planet’s diameter, they cannot place accurate constraints on a planet’s mass. For this, the Radial Velocity method (as noted earlier) is the most reliable, where astronomers look for signs of “wobble” in a star’s orbit to the measure the gravitational forces acting on them (which are caused by planets).
In short, the transit method has some limitations and is most effective when paired with other methods. Nevertheless, it remains the most widely-used means of “primary detection” – detecting candidates which are later confirmed using a different method – and is responsible for more exoplanet discoveries than all other methods combined.
Examples of Transit Photometry Surveys:
Transit Photometry is performed by multiple Earth-based and space-based observatories around the world. The majority, however, are Earth-based, and rely on existing telescopes combined with state-of-the-art photometers. Examples include the Super Wide Angle Search for Planets (SuperWASP) survey, an international exoplanet-hunting survey that relies on the Roque de los Muchachos Observatory and the South African Astronomical Observatory.
There’s also the Hungarian Automated Telescope Network (HATNet), which consists of six small, fully-automated telescopes and is maintained by the Harvard-Smithsonian Center for Astrophysics. The MEarth Project is another, a National Science Foundation-funded robotic observatory that combines the Fred Lawrence Whipple Observatory (FLWO) in Arizona with the Cerro Tololo Inter-American Observatory (CTIO) in Chile.
Then there’s the Kilodegree Extremely Little Telescope (KELT), an astronomical survey jointly administered by Ohio State University, Vanderbilt University, Lehigh University, and the South African Astronomical Society (SAAO). This survey consists of two telescopes, the Winer Observatory in southeastern Arizona and the Sutherland Astronomical Observation Station in South Africa.
In terms of space-based observatories, the most notable example is NASA’s Kepler Space Telescope. During its initial mission, which ran from 2009 to 2013, Kepler detected 4,496 planetary candidates and confirmed the existence of 2,337 exoplanets. In November of 2013, after the failure of two of its reaction wheels, the telescope began its K2 mission, during which time an additional 515 planets have been detected and 178 have been confirmed.
The Hubble Space Telescope also conducted transit surveys during its many years in orbit. For instance, the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) – which took place in 2006 – consisted of Hubble observing 180,000 stars in the central bulge of the Milky Way Galaxy. This survey revealed the existence of 16 additional exoplanets.
Other examples include the ESA’s COnvection ROtation et Transits planétaires (COROT) – in English “Convection rotation and planetary transits” – which operated from 2006 to 2012. Then there’s the ESA’s Gaia mission, which launched in 2013 with the purpose of creating the largest 3D catalog ever made, consisting of over 1 billion astronomical objects.
In March of 2018, the NASA Transiting Exoplanet Survey Satellite (TESS) is scheduled to be launched into orbit. Using the transit method, TESS will detect exoplanets and also select targets for further study by the James Webb Space Telescope (JSWT), which will be deployed in 2019. Between these two missions, the confirmation and characterization or many thousands of exoplanets is anticipated.
Thanks to improvements in terms of technology and methodology, exoplanet discovery has grown by leaps and bounds in recent years. With thousands of exoplanets confirmed, the focus has gradually shifted towards the characterizing of these planets to learn more about their atmospheres and conditions on their surface.
In the coming decades, thanks in part to the deployment of new missions, some very profound discoveries are expected to be made!
We have many interesting articles about exoplanet-hunting here at Universe Today. Here’s What are Extra Solar Planets?, What are Planetary Transits?, What is the Radial Velocity Method?, What is the Direct Imaging Method?, What is the Gravitational Microlensing Method?, and Kepler’s Universe: More Planets in our Galaxy than Stars.
Astronomy Cast also has some interesting episodes on the subject. Here’s Episode 364: The COROT Mission. | 0.938684 | 3.968943 |
Nebulas: Pillars of Creation (03:04)
In one of the most famous photographs taken by the Hubble telescope, three enormous columns of dust and gas, seven light years long, are part of the Eagle Nebula. Nebulas take on images familiar to humans such as flowers, insects, or people.
Orion Nebula and Astrophotography (08:25)
The Orion Nebula is the most active area of star formation in the galaxy. Photographs of nebulas offer an important niche at the nexus of art and science. Astrophotographers use digital cameras that emulate color vision in the human eye.
Kinds of Nebulas (01:34)
Nebulas are classified into five kinds: H-II, reflection, planetary, supernova remnants, and dark nebulas.
Interstellar Medium (ISM) (02:04)
The stars in the Milky Way are very far apart. The space between the stars contains a very diffuse medium of gas and dust astronomers call the interstellar medium. This medium consists of neutral hydrogen gas, molecular gas, ionized gas, and dust grains.
Star-Forming Nebulas (02:29)
Gravity goes to work on interstellar medium causing it to condense while creating temperatures of a star. The new stars burst into existence in colorful brilliance.
Nebulas: Sizes, Shapes, and Colors (03:39)
As new stars are born within the nebulas, they sometimes shoot out spectacular jets. Nebulas display a wide variety of bubbles, shockwaves, pillars, and mountains. Infrared images show nebulas in extraordinary colors and shapes.
Electromagnetic Spectrum (03:12)
The electromagnetic spectrum visually classifies types of radiation, energy that travels and spreads out as it goes. Included on the spectrum are visible light, radio waves, microwaves, infrared and ultraviolet light, X-rays and gamma-rays.
Nebular Photography (02:23)
Astronomers take Hubble photographs of the Pillars of Creation and then assemble the components into a full color image that reveals more than the sum of its parts. Resultant images are in the visible light spectrum.
Planetary Nebulas (02:38)
The Ring Nebula is considered a prototype for planetary nebulas. Nebula displays of dramatic color and shape are what remains of a dying star.
Helix Nebula (06:48)
There are an estimated 10,000 planetary nebulas in Earth's galaxy. The Helix Nebula, often called the "Eye of God," is only 400 light years from Earth and has been studied intensely. Astronomers are perplexed by the astonishing shapes of planetary nebulas.
Supernova Remnants (03:52)
In 1054, a star exploded and remained visible for 29 days. One thousand years later, we call these supernova remnants the Crab Nebula. At its center is a pulsar.
Life Cycle of the Universe (02:29)
The gas that is expelled into space as supernova remnants and planetary nebulas returns to the interstellar medium where it becomes raw material for future generations of stars. The life cycle of the universe continues.
Credits: Nebulas (00:23)
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Humans have been seeing strange things on the surface of Mars for centuries. From the 1700s up through the present day, widespread fame has been available to anyone able to produce even the slightest bit of flimsy evidence that there’s Martian life.
A perspective view showing the so-called 'Face on Mars' located in the Cydonia region. The image shows a remnant massif thought to have formed via landslides and an early form of debris apron formation. The massif is characterized by a western wall that has moved downslope as a coherent mass. The image, created with data from the Mars Express orbiter, was released Sept. 21, 2006
The most recent example was this week’s supposed revelation that a secret Mars base
, inhabited either by humans or Martians, can be seen in a photo of the Red Planet’s surface taken by an orbiting spacecraft.
But scientific rigor has always stepped in to prove that these objects are not really there. In this vast and lonely universe, are Earthlings just desperate for next-door neighbors to play with? Looking back over the long history of Martian illusions (and human delusions), it certainly seems so. [7 Things that Create Great Space Hoaxes]
Land and sea
In 1784, Sir William Herschel, a famous British astronomer, wrote that dark areas on Mars were oceans and lighter areas were land. He speculated that Mars was inhabited by intelligent beings who “probably enjoy a situation similar to our own.” Herschel’s theory prevailed for a century, with other astronomers claiming that vegetation could even be observed in the lighter-colored regions taken to be land. Fortunately for Herschel, his other contributions to astronomy — which earned him the honor of being the namesake of two powerful observatories — were great enough to keep his theories on Martians near the bottom of his biography.
Canali vs. canals
During Mars’ close approach to Earth in 1877, the Italian astronomer Giovanni Schiaparelli peered through his telescope and observed grooves or channels on the Red Planet’s surface. The Italian word he used for them, “canali,” was translated to “canals”
in English, leading many in the English-speaking world to conclude that Mars had intelligent life that had built a system of waterways.
That misconception was popularized by an astronomer named Percival Lowell, who in 1895 presented drawings of the canals in a book, titled “Mars,” and argued his full theory in a second book, “Mars as the Abode of Life,” in 1908. The inaccuracy was further fueled, historians say, by excitement over the construction of the Suez Canal, an engineering marvel of the era completed in 1869.
The theory was debunked in the early twentieth century, when it was demonstrated that the “canals” were merely optical illusions: when viewed through poor-quality telescopes, pointlike features, such as Mars’ mountains and craters, appear to be joined together by straight lines. Later, spectroscopic analysis of the light coming from Mars showed that there was no water on its surface. [Would Humans Born On Mars Grow Taller than Earthlings?
Martian canals as depicted by Percival Lowell
In 1921, Guglielmo Marconi, inventor of the first radio telegraph system, claimed to hear signals that he thought might be Martian. The next year and again in 1924, at times when Mars swung relatively close to Earth, the U.S. government asked all radio stations to go silent so that they could listen out for any Martian transmissions coming our way.
But ET radio was silent.
It all started back in 1976, when NASA released an image of an interesting mountain on Mars, taken by the Viking 1 spacecraft, complete with a caption that described the formation as appearing to have eyes and nostrils. More than thirty years later, the “Face on Mars” still inspires myths and conspiracy theories, with many people believing it to be an artificial structure built by an ancient Martian civilization.
From a bird’s-eye view, shadows on the mountain really do make it look like a face. From other angles, however — angles seen in photos taken by the Mars Express Orbiter, among other spacecraft — the mountain is clearly just that, and doesn’t look much like a face at all.
“Pareidolia” is the scientific term for seeing faces (or other significant objects) where they aren’t. Face pareidolia happens, scientists say, as a byproduct of our heightened sensitivity to the details of human faces. Takeo Watanabe of the Boston University Visual Sciences Laboratory put it this way: “We’ve over-learned human faces so we see them where they aren’t.” [Face On Mars: Why People See What’s Not There
NASA'S Mars Exploration Rover Spirit captured this westward view from atop a low plateau where Spirit spent the closing months of 2007.
In a photo snapped by the Mars rover Spirit in 2007, there appears to be a human being wearing a robe and kneeling in prayer. It is, of course, a rock, and merely morphs into human form in our brains because of pareidolia, as explained above.
Bio Station Alpha
This week, yet another smidgen of evidence arose that, on first examination, seemed to support the notion that there’s life on Mars. In a viral Youtube video, a self-described “armchair astronaut” claimed to have identified a human (or alien) base on Mars, which he dubbed Bio Station Alpha. He found a somewhat mysterious linear structure that appears to be on the Red Planet’s surface as seen in Google Mars, a new map program created from compiled satellite images of the planet.
Astronomers immediately identified the structure — in actuality just a white, pixelated streak — as an artifact deposited by a cosmic ray in the image sensor of the camera that snapped the photo. “With space images that are taken outside our magnetosphere, such as those taken by orbiting telescopes, it’s very common to see these cosmic ray hits,” said Alfred McEwen, a planetary geologist at the Lunar and Planetary Lab at the University of Arizona and the director of the Planetary Imaging Research Laboratory.
are energetic particles emitted by the sun. They deposit electric charge in camera pixels as they penetrate them, momentarily saturating them and creating a white streak in any photo snapped at the time.
When the raw image file was converted to a JPEG for use in Google Mars, McEwen said compression probably caused the cosmic ray artifact to become more rectangular and “Bio Station”-like. This was subsequently proven to be the case, when the original source photo
that Google used was identified. It contained an obvious cosmic ray artifact, which, when processed, turned into the structure that the “armchair astronaut” mistook for a Mars base. | 0.915356 | 3.418501 |
On the morning of Sunday, August 12th, 2018, NASA launched the Parker Solar mission, which it describes as being “to touch the face of the Sun”. It will be the first mission to fly through the Sun’s corona – the hazardous region of intense heat and solar radiation in the Sun’s atmosphere that is visible during an eclipse, and it will gather data that could help answer questions about solar physics that have puzzled scientists for decades. Over the course of its initial 7-years the Parker Solar Probe mission will allow us to better understand the fundamental processes going on in, on, and around the Sun, improving our understanding how our solar system’s star influences, affects and changes the space environment, through which we travel as the Earth orbits the Sun.
The probe and mission are named for Dr Eugene Parker, an American solar astrophysicist, who in 1958 first posited the theory of the supersonic solar wind, and who also predicted the Parker spiral shape of the solar magnetic field in the outer solar system. Now 91, he was present at NASA’s Kennedy Space Centre as a distinguished guest of the agency, to witness the probe’s launch, the mission (and vehicle) being the first in NASA’s history to be named after a still-living person.
Lift-off came at 03:31 EDT (6:31 GMT / 7:31 BST) on Sunday, August 12th, after the initial launch attempt was scrubbed on Saturday, August 11th, when a troubled countdown was halted just one-minute, 55 seconds before the engines on the United Launch Alliance (ULA) Delta 4 Heavy rocket were to ignite. The halt was called following a gaseous helium red pressure alarm, and investigations into its cause extended beyond the 65-minute launch window, resulting in the launch scrub.
The Sunday morning launch countdown proceeded without any significant hitches, and the Delta 4 Heavy – the most powerful rocket in ULA’s fleet of launch vehicles, comprising 3 Delta 4 first stages strapped side-by-side, the outer two functioning as “strap-on boosters” – lit up the Florida coastline as it took to the early morning skies.
Although a flight to the Sun might sound an easier proposition than reaching the outer solar system, it actually isn’t; it actually requires 55 times more launch energy than a launch to Mars. Hence why the relative small and light Parker Solar Probe, weighing just 685 kg (1,510 lb) at launch, required the massive Delta 4 and a rarely-used Star 48BV variant of the Payload Assist Module (PAM).
Originally developed as the upper stage for Delta 2 launch vehicles in the 1965, the Star family of solid-fuel PAM units were commonly used with the space shuttle for satellite launches from orbit: the shuttle would carry them aloft, release the PAM / Satellite combination, then move to a safe distance before the PAM motor was ignited to push the satellite on to its require Earth orbit. For the Parker Solar Probe, the Star 48BV was used to impart as much velocity as possible into the vehicle at is starts on it journey.
What makes a flight to the Sun so hard is that the Earth is moving “sideways” relative to the Sun at about 107,000 km/h (67,000 mph), and the probe has to cancel out a whopping 84,800 km/h (53,000 mph) of that “sideways” motion as it makes its way to the Sun in order to achieve orbit. At the same time, the probe needs to gain velocity as it moves in towards the centre of the solar system in order for it to balance the Sun’s enormous gravitational influence and achieve the required elliptical orbit.
The use of the Delta 4 / Star 48BV combination got both of these requirements started, by pushing the probe towards Venus in an arc that will both start to shed the “sideways” velocity, whilst also accelerating the craft in towards the Sun. But it will be Venus that does the real grunt work for the mission.
On October 1st, 2018, the probe will make the first of a series of flybys of Venus, where it will use the Venusian gravity to shed still more of the angular velocity imparted by Earth’s orbit and increase its velocity towards the Sun.
In all, seven such fly-bys of Venus will occur over the 7 year primary mission for the probe, and while only the first is required to shunt the vehicle into its core heliocentric orbit, the remaining six play an important role in both maintaining the vehicle’s average velocity across the span of the mission and in gradually shrinking its elliptical orbit around the Sun as the mission progresses.
The first pass around the Sun – and the start of the science mission – will occur in November / December 2018. At perihelion, the vehicle will be just 6.2 million km (3.85 million mi) from the Sun’s photosphere (what we might call its “surface”). During this time, the vehicle will be well within the corona, and will also temporarily become the fastest human-made vehicle ever made, achieving a velocity of around 700,000 km/h (430,000 mph) – that’s 200 km per second (120 mi/s), or the equivalent of travelling between London and Tokyo in around 50 seconds! At aphelion – the point furthest from the Sun, and brushing Earth’s orbit, the craft will be travelling a lot slower.
The corona is a very hot place – hotter than the “surface” of the Sun, however, it is also comparatively thin as far as an “atmosphere” goes. The distance at which Parker Solar Probe will be travelling from the Sun at perihelion, combined with its speed, mean that the ambient heat of the corona isn’t a significant issue. Direct sunlight radiating out from the Sun, however, is a significant problem. | 0.832596 | 3.586617 |
What is the speed that dust is ejected from the nucleus of a comet? (into the coma)
An expert replied to me "0.6 km/s
", but I would very much prefer if I would measure it!
Pointing at the comet nucleus, I should see some solar spectrum reflected on the dust. Dust would be thrown out in every direction, so Doppler-Fizeau effect should "widen" any absorption lines from the solar spectra.
Am I correct in thinking that at a phase angle of 35º, the widest an absorption line could be widened is 2*cos^2(35º) * 2*(0,6/c)*wavelength ? So for H-alpha, this is still 1/3 of the resolution of my Lhires III
Comet C/2014 Q2 (Lovejoy) is also brightest when it is closest to the Earth... ...At which time, the comet is also moving apparently fastest..
I managed to track this comet on 2015-01-04, but it was too faint for a spectrum in 5 minutes exposure
This could be an interesting project for when the Comet and the Moon (reference spectrum) are in the sky!.. But I might not have enough resolution for this, no?
Do high-resolution spectra of comets show reflected features from solar spectrum (similar to gaseous planets)? | 0.839943 | 3.262491 |
eso1228 — Science Release
Dark Galaxies of the Early Universe Spotted for the First Time
11 July 2012
For the first time, dark galaxies — an early phase of galaxy formation, predicted by theory but unobserved until now — may have been spotted. These objects are essentially gas-rich galaxies without stars. Using ESO’s Very Large Telescope, an international team thinks they have detected these elusive objects by observing them glowing as they are illuminated by a quasar.
Dark galaxies are small, gas-rich galaxies in the early Universe that are very inefficient at forming stars. They are predicted by theories of galaxy formation and are thought to be the building blocks of today’s bright, star-filled galaxies. Astronomers think that they may have fed large galaxies with much of the gas that later formed into the stars that exist today.
Because they are essentially devoid of stars, these dark galaxies don’t emit much light, making them very hard to detect. For years astronomers have been trying to develop new techniques that could confirm the existence of these galaxies. Small absorption dips in the spectra of background sources of light have hinted at their existence. However, this new study marks the first time that such objects have been seen directly.
“Our approach to the problem of detecting a dark galaxy was simply to shine a bright light on it.” explains Simon Lilly (ETH Zurich, Switzerland), co-author of the paper. “We searched for the fluorescent glow of the gas in dark galaxies when they are illuminated by the ultraviolet light from a nearby and very bright quasar. The light from the quasar makes the dark galaxies light up in a process similar to how white clothes are illuminated by ultraviolet lamps in a night club.”
The team took advantage of the large collecting area and sensitivity of the Very Large Telescope (VLT), and a series of very long exposures, to detect the extremely faint fluorescent glow of the dark galaxies. They used the FORS2 instrument to map a region of the sky around the bright quasar HE 0109-3518, looking for the ultraviolet light that is emitted by hydrogen gas when it is subjected to intense radiation. Because of the expansion of the Universe, this light is actually observed as a shade of violet by the time it reaches the VLT.
“After several years of attempts to detect fluorescent emission from dark galaxies, our results demonstrate the potential of our method to discover and study these fascinating and previously invisible objects,” says Sebastiano Cantalupo (University of California, Santa Cruz), lead author of the study.
The team detected almost 100 gaseous objects which lie within a few million light-years of the quasar. After a careful analysis designed to exclude objects where the emission might be powered by internal star-formation in the galaxies, rather than the light from the quasar, they finally narrowed down their search to 12 objects. These are the most convincing identifications of dark galaxies in the early Universe to date.
The astronomers were also able to determine some of the properties of the dark galaxies. They estimate that the mass of the gas in them is about 1 billion times that of the Sun, typical for gas-rich, low-mass galaxies in the early Universe. They were also able to estimate that the star formation efficiency is suppressed by a factor of more than 100 relative to typical star-forming galaxies found at similar stage in cosmic history.
“Our observations with the VLT have provided evidence for the existence of compact and isolated dark clouds. With this study, we’ve made a crucial step towards revealing and understanding the obscure early stages of galaxy formation and how galaxies acquired their gas”, concludes Sebastiano Cantalupo.
The MUSE integral field spectrograph, which will be commissioned on the VLT in 2013, will be an extremely powerful tool for the study of these objects.
Fluorescence is the emission of light by a substance illuminated by a light source. In most cases, the emitted light has longer wavelength than the source light. For instance, fluorescent lamps transform ultraviolet radiation — invisible to us — into optical light. Fluorescence appears naturally in some compounds, such as rocks or minerals but can be also added intentionally as in detergents that contain fluorescent chemicals to make white clothes appear brighter under normal light.
Quasars are very bright, distant galaxies that are believed to be powered by supermassive black holes at their centres. Their brightness makes them powerful beacons that can help to illuminate the surrounding area, probing the era when the first stars and galaxies were forming out of primordial gas.
This emission from hydrogen is known as Lyman-alpha radiation, and is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. It is a type of ultraviolet light. Because the Universe is expanding, the wavelength of light from objects gets stretched as it passes through space. The further light has to travel, the more its wavelength is stretched. As red is the longest wavelength visible to our eyes, this process is literally a shift in wavelength towards the red end of the spectrum — hence the name ‘redshift’. The quasar HE 0109-3518 is located at a redshift of z = 2.4, and the ultraviolet light from the dark galaxies is shifted into the visible spectrum. A narrow-band filter was specially designed to isolate the specific wavelength of light that the fluorescent emission is redshifted to. The filter was centered at around 414.5 nanometres in order to capture Lyman-alpha emission redshifted by z=2.4 (this corresponds to a shade of violet) and has a bandpass of only 4 nanometres.
The star formation efficiency is the mass of newly formed stars over the mass of gas available to form stars. They found these objects would need more than 100 billion years to convert their gas into stars. This result is in accordance with recent theoretical studies that have suggested that gas-rich low-mass haloes at high redshift may have very low star formation efficiency as a consequence of lower metal content.
This research was presented in a paper entitled "Detection of dark galaxies and circum-galactic filaments fluorescently illuminated by a quasar at z=2.4", by Cantalupo et al. to appear in Monthly Notices of the Royal Astronomical Society.
The team is composed of Sebastiano Cantalupo (University of California, Santa Cruz, USA), Simon J. Lilly (ETH Zurich, Switzerland) and Martin G. Haehnelt (Kavli Institute for Cosmology, Cambridge, United Kingdom).
The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
University of California
Santa Cruz, USA
Tel: +1 831 459 5891
Simon J. Lilly
Institute for Astronomy, ETH Zurich
Tel: +41 44 633 3828
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591 | 0.904997 | 4.014541 |
Jan 25, 2013
The MESSENGER space probe continues to illustrate the Electric Universe theory.
MESSENGER has been in orbit around Mercury since March 17, 2011. Since that time, it has sent hundreds of close-up images of the surface, revealing features and topography that assure Mercury’s kinship with the Solar System’s other celestial bodies: its surface is pitted, gouged, punctured, and grooved in ways so like its sisters and brothers that telling it apart from some of them would be difficult.
Past electrical activity on Mercury is evident in several locations around the planet. Indeed, the entire planet could be said to exhibit nothing but electrical effects. The etched furrows radiating outward from some craters denote the path of untold numbers of electric filaments as they danced a fiery dance across the surface. On Earth, those filaments would have been the largest lightning strikes ever witnessed.
Terrain features, such as those on Mercury would be difficult to reproduce in the laboratory, unless electricity were brought into the picture. Not the electricity needed to operate a compressed air gun firing hypersonic projectiles, but that needed to act as a high voltage discharge.
In an experiment at Vemasat Laboratories, Dr. C. J. Ransom created the same kind of etched furrow by shocking a thin layer of magnesium silicate with a 120 milliamp, 12,000 volt discharge for five seconds. He created radial gouges on a small scale equivalent to Mercury at the large scale. As pointed out in previous Pictures of the Day, Nobel Laureate Hannes Alfvén thought that electrical (plasma) phenomena could be scaleable by as much as 14 orders of magnitude.
Since an electric arc is composed of rotating filaments, if electricity were involved in Mercury’s evolution, it would have manifested in many ways. One of those ways would be to act like a plasma “drill bit,” cutting steep crater sidewalls, while sometimes leaving a “pinched up” mound in the center. Multiple filaments would cut one crater within another, often with one or more craters on the rims, such as in the image above.
What is most remarkable about Mercury and other members of the Solar System are the numerous crater chains that abound throughout the population. From Phobos to Phoebe; from Mars to Miranda, planets and moons are pocked with holes that run in long lines, sometimes for hundreds of kilometers. The common explanation for them is that a string of meteoroids impacted one after another, one behind the other.
The coincidence necessary for that effect notwithstanding, the absence of distortion in adjoining crater walls calls the theory into question. Add to that the twists, turns, loops, and braids that can be seen in many of them and the idea that rocks falling from space caused these features falls apart.
Anyone who has made an electric arc device called a “Jacob’s Ladder” knows how the line of craters could have formed. A Jacob’s ladder is constructed by placing a stiff copper wire on each standoff of a neon sign transformer and then bending them in toward each other until they form an ever-widening “V” from bottom to top. When the current is turned on, an electric arc begins at the lowest level of the V and then rises up to the top, growing longer across the widening gap until it disconnects with a snap, only to immediately begin again. If a piece of paper is held between the two limbs of the V while the electric arc travels upward, a row of pinholes will be found burned lengthwise into the paper.
Electric arcs traveling across a conductive medium vary in strength from millisecond to millisecond, so they burn chains of craters instead of smooth channels. In fact, the “smooth” channels seen on many objects are crater chains packed so closely together that they can no longer be distinguished.
There are more examples from MESSENGER that reveal Mercury’s catastrophic past. It is certain that additional evidence supporting the Electric Universe paradigm of planetary scarring will come to light. | 0.86982 | 3.791852 |
Saturday, August 31, 2019
The Oort Cloud
The Oort Cloud The Oort cloud is a vast swarm of some 2 trillion comets orbiting our star in the most distant reaches of our solar system, extending from beyond the orbits of Neptune and Pluto out to 100,000 times the Earth-Sun distance. Almost one-third the distance to the nearest star. While the planets are confined to a flattened disk in the solar system, the Oort cloud forms a spherical shell centered on the Sun, which gradually flattens down to an extended disk in the inner region, called the Kuiper belt.Bright comets observed through telescopes or with the naked eye get thrown out of the Oort cloud or Kuiper belt, and become visible when they get close to enough so that the Sun's energy can transform the surface ices into gases. These gases drag off the embedded dust, and we see the light reflected from the dust as a tail. Comets are the leftover icy building blocks from the time of planet formation, which formed in the region of the outer planets. Essentially thesecomets are d irty snowballs, composed primarily of water ice, with some carbon monoxide and other ices, in addition to interstellar dust.When their orbits passed close enough to the giant planets to be affected, some were thrown toward the Sun and some were tossed outward toward the distant reaches of the solar system, the spherical swarm we now call the Oort cloud. Some of the comets sent inward hit the inner rocky planets, and probably contributed a significant amount of ocean water and organic material, the building blocks of life, to Earth. Comets that live in the Oort cloud are especially important scientifically because they have been kept in a perpetual deep freeze since the formation of our solar system 4. 6 billion years ago.This means that they preserve, nearly intact, a record of the chemical conditions during the first few million years of the solar system's history, and can be used to unravel our solar system's origins much like an archaeologist uses artifacts to decipher an ancient civilization. The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU (0. 03 and 0. 08 ly) to as far as 50,000à AU (0. 79à ly) from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 AU (1. 58 and 3. 16 ly). The region can be subdivided into a spherical outer Oort cloud of 20,000ââ¬â50,000 AU (0. 2ââ¬â0. 79 ly), and a doughnut-shaped inner Oort cloud of 2,000ââ¬â20,000 AU (0. 03ââ¬â0. 32 ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune. The inner Oort cloud is also known as the Hills cloud, named after J. G. Hills, who proposed its existence in 1981. Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo; it is seen as a possible source of new comets to resupply the relatively tenuous outer cloud as the latter's nu mbers are gradually depleted.The Hills cloud explains the continued existence of the Oort cloud after billions of year The outer Oort cloud is believed to contain several trillion individual objects larger than approximately 1à km (0. 62à mi) (with many billions with absolute magnitudes brighter than 11ââ¬âcorresponding to approximately 20à km (12à mi) diameter), with neighboring objects typically tens of millions of kilometres apart. Its total mass is not known with certainty, but, assuming that Halley's comet is a suitable prototype for all comets within the outer Oort cloud, the estimated combined mass is 3? 025à kg (7? 1025à lb or roughly five times the mass of the Earth). Earlier it was thought to be more massive (up to 380 Earth masses), but improved knowledge of the size distribution of long-period comets has led to much lower estimates. The mass of the inner Oort Cloud is not currently known. If analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of various ices such as water, methane, ethane, carbon monoxide and hydrogen cyanide.However, the discovery of the object 1996à PW, an asteroid in an orbit more typical of a long-period comet, suggests that the cloud may also contain rocky objects. Analysis of the carbon and nitrogen isotope ratios in both the Oort cloud and Jupiter-family comets shows little difference between the two, despite their vastly separate regions of origin. This suggests that both originated from the original protosolar cloud,a conclusion also supported by studies of granular size in Oort-cloud comets by the recent impact study of Jupiter-family comet. | 0.879271 | 3.937376 |
Defining science might not be as easy as initially thought. Anything with centuries long history, one that involves the intricacies and complexities of religion, philosophy, and other avenues of human belief, is seldom easy to capture in just a handful of paragraphs. But thankfully, science, as it is seen today, has a number of distinct characteristics that separates it from other disciplines and other means of acquiring knowledge about the universe. What are some of these distinguishable traits?
Science seeks to explain things. Why, for example, if one throws a ball across an open field will it arch in a parabola, as opposed to a circle or a square, and then fall back to the ground? Why doesn’t the ball just keep flying away into the sky? No doubt Newton’s law of universal gravitation will help answer that question. This is why human beings do science in the first place. It helps build knowledge and an understanding of how the natural world works, and learning such things have had a good track record of elevating the quality of life, increasing human knowledge, and assisting and benefiting human beings in many important ways. Science, secondly, emphasizes predictability. The laws of nature allow scientists to predict what will happen under certain conditions. The apprehension of the law of gravity, for example, allows for scientists to predict that if one throws a ball up in the sky it will no doubt fall back down. Third, and just as important, is that of testability. A scientific claim allows itself to be analyzed against the real world, and invites scientists to examine a hypothesis to see whether or not it can be supported or falsified by the data of actual experience. Testability can thus lead to one of two conclusions: confirmation or refutation. It might lead to confirmation given that empirical evidence supports a hypothesis or, if a hypothesis lacks empirical support, then possibly refutation. A scientific claim must also be falsifiable. It must be open to refutation perhaps by facts supporting another hypothesis that could better explain phenomena. If one considers Kepler’s Laws that describe the motion of the planets he will realize that they are foundational to much of modern astronomy and physics. Kepler’s Law of Orbits, for instance, says that all planets move in elliptical orbits with the sun at one of the two foci. However, if scientists discovered planets orbiting in squares then Kepler’s Law of Orbits would be considered false, hence scrapped as an adequate theory.
No scientific theory is ever “proven” in any absolute sense simply because science continues to seek after new evidence. What one might consider a compelling theory today might be overturned or revised tomorrow. This is not to say that science and scientific theory are somehow unreliable, because many theories are accepted on the basis of compelling evidence, as well as because of the fact that further scientific investigation continues to support them (Big Bang theory, for example). A good scientist must therefore always be ready and open to rejecting his or her theories should they fail to account for new or reconsidered evidence. Thus, generally speaking, science hopes to understand the history of the universe and how the natural world works, with observable physical evidence being the basis from which we can learn about the world.
The question then is, how might one understand creation-science given this definition and understanding of science? We will return to this question shortly after we’ve defined what creation-science is.
One proponent of the view, Duane Gish, encapsulates the general idea of what creation-science is promoting,
“By creation we mean the bringing into being by a supernatural Creator of the basic kinds of plants and animals by the process of sudden, or fiat, creation…We do not know how God created, what processes He used, for God used processes which are not now operating anywhere in the natural universe. This is why we refer to divine creation as Special Creation. We cannot discover by scientific investigation anything about the creative processes used by God” (1).
Creation-science is often based on literal interpretations and inerrantist presuppositions of the narratives of particular religious texts, specifically the Genesis text of the Bible (2). Proponents argue that the Earth is just a few thousand years old (roughly 6 000 to 10 000 years), that Adam and Eve are the progenitors of the entire human race, and that there really was a global flood that encompassed the entire Earth as presented in the story of Genesis 6. Naturally, such a proponent will oppose evolutionary theory as well as any scientific evidence suggesting that there never was a global flood and that the Earth is at least four billion years old. According to Loren Haarsma, a physicist at the theistic think tank Biologos,
“Some Christians, often called ‘Young Earth creationists,’ reject evolution in order to maintain a semi-literal interpretation of certain biblical passages. Other Christians, called ‘progressive creationists,’ accept the scientific evidence for some evolution over a long history of the earth, but also insist that God must have performed some miracles during that history to create new life-forms. Intelligent design, as it is promoted in North America is a form of progressive creation. Still other Christians, called ‘theistic evolutionists’ or ‘evolutionary creationists,’ assert that the scientific theory of evolution and the religious beliefs of Christianity can both be true” (3).
Proponents of creation science will argue that the evidence in the world supports both a young Earth an a universal flood. It was a view argued for by the Canadian Seventh Day Adventist and amateur geologist George McCready Price (1870-1963) in his books The New Geology (1923) and Illogical Geology (1906) which seemed convincing to Christians readers who lacked training in geology. It wasn’t long after that Henry Morris (1918-2006) and John Whitcomb revised and updated his 1923 work The New Geology. Morris and Whitcomb soon released their own book The Genesis Flood in 1961. The duo argued that, on the basis of their interpretation of the Bible, the Earth was 6000 years old, that the fall of man transformed nature by initiating the operation of the second law of thermodynamics, and that Noah’s flood was the correct explanation for most of the geological evidence and fossilization that scientists observe today. The creation science movement didn’t stop there as since the 1960s three major Young Earth Creationist (YEC) organizations have accumulated a following and thus exerted some influence on the consciousness of religious believers. These notably being The Institute for Creation Research (ICR) (founded in 1972 by Henry Morris and now run by his son John), a larger international organization Answers in Genesis (founded by the Australian Ken Ham) and Creation Ministries International (founded in Australia in 2006).
The claimed evidence that YEC scientists have offered for their Young-Earth views have received little scientific response from mainstream scientists. This is because, on scientific grounds, their claims are unanimously viewed as problematic evidentially and methodologically. Likewise the consensus of professional biblical scholars view a YEC biblical interpretation as anachronistic as well as an unwarranted reading of the opening chapters of Genesis.
Although creation science has been quite popular for many religious believers adherence among the general public, according to some statistics, has dropped quite significantly. For example, in the US, where creation-science has generally held a notable presence, only 38% of Americans believed God created life some time in the past 10 000 years, making it the lowest figure in 35 years (4). Only 22% of Canadians and 17% of Britons believe similarly (5). Nonetheless, despite it diminishing status, creation-scientists will argue that creation-science is legitimate science and therefore must be taught in public classrooms. Critics, however, observe that what is masqueraded as “science” (creation-science) it is actually a form of religion, specially one constructed upon “dogmatic biblical literalism” (6).
Responses to Creation-Science.
Contemporary scientific consensus opposes the views proposed by creation-scientists, and criticisms of creation-science can been found in both Christian and non-Christian camps (7) (8). The National Science Teachers Association, for example, opposes teaching creationism as science (9). Other prominent scientific organizations such as the American Anthropological Association, Association for Science Teacher Education, the National Association of Biology Teachers, the Geological Society of America, the American Geosciences Institute, the American Geophysical Union, among numerous other professional teaching and scientific societies, have opposed scientific creationism and view it as a pseudoscience. According to the American Academy of Religion, creation-science should not be taught in science classes given that is ,
“represent[s] worldviews that fall outside of the realm of science that is defined as (and limited to) a method of inquiry based on gathering observable and measurable evidence subject to specific principles of reasoning” (10).
One of the major critiques leveled against creation-science is that is denies an overwhelming amount of empirical evidence and scientific consensus. As the Royal Society states,
“a belief that all species on Earth have always existed in their present form is not consistent with the wealth of evidence for evolution, such as the fossil record. Similarly, a belief that the Earth was formed in 4004 BC is not consistent with the evidence from geology, astronomy and physics that the solar system, including Earth, formed about 4600 million years ago.”
This includes creation-science’s hypotheses conflicting with the dating methods of geology, astronomy, cosmology, and paleontology. For example, significant difficulties sustaining a young Earth view is only enhanced by the age of the earliest pottery discovered, the age of ice cores, the oldest known trees, and the layers of silt deposit in Lake Suigetsu – all of which point to a far older Earth than creation-scientists have argued for. Some creation-scientists, aware of the evidence for an older Earth, have argued that the Earth was created with the appearance of age. Although one could entertain that claim theologically it is, however, problematic scientifically because it renders the hypothesis unfalsifiable. On such a claim no evidence could ever possibly be discovered or produced that could falsify the claim that God created the Earth with an appearance of age, and the creation-scientist could always dismiss any evidence to the contrary stating that God just made it that way.
Another scientific criticism leveled against creation-science is that many of his beliefs involve supernatural forces that lie outside of nature (they depend on supernatural intervention) and, as a result, do not allow for predictions. Thus, many of the claims and beliefs that creation-scientists hold can neither be confirmed nor disproved by scientists. According to the National Academy of Science,
“In science, explanations must be based on naturally occurring phenomena. Natural causes are, in principle, reproducible and therefore can be checked independently by others. If explanations are based on purported forces that are outside of nature, scientists have no way of either confirming or disproving those explanations” (11)
… “they begin with an explanation that they are unwilling to alter—that supernatural forces have shaped biological or Earth systems—rejecting the basic requirements of science that hypotheses must be restricted to testable natural explanations. Their beliefs cannot be tested, modified, or rejected by scientific means and thus cannot be a part of the processes of science” (12).
Creation-science thus fails, at least on this level, to makes its case in favour of it being considered a viable science. This not only goes for creation-science, but also other untestable and unfalsifiable explanations of the world derived from myths, as well as personal, philosophical, and religious beliefs. This is not to say that any of those beliefs are false, but rather they cannot be said to be scientific beliefs.
Creation-science also fails the criteria of falsifiability. A scientific theory puts itself in the firing line, so to speak, through opening itself up to being falsified on the basis of new information and facts. Creation-science doesn’t do this, rather, advocates of creation-science seem to be at work constantly protecting their views against threats, hence why they’ve been criticized for promoting and inventing ad hoc hypotheses to save their assumptions (13).
Further, perhaps more of a taint to reputation than as opposed to an actual scientific critique, dishonesty and a lack of integrity can be found within the works of creation-science advocates. One way to see this is in their often blatant misquoting of authorities. According to philosopher of science Michael Ruse, one finds this in their treatment of evolutionary theory,
“Almost invariably, the creationists work exclusively with discoveries and claims of evolutionists, twitching their claims to their own ends… When new counter-empirical evidence is discovered, creation scientists appear to pull back, refusing to allow their position to be falsified” (14).
One creationist, Gary Parker, misquotes Richard Lewontin, and gives the impression that Lewontin actually viewed the human hand and eye as evidence for God’s design (15). This is an odd claim given that Lewotin was known for his materialistic disposition as he once penned that “materialism [in science] is absolute, for we cannot allow a Divine foot in the door” (16). Instead, Lewontin merely penned that such was rather a belief held by people prior to Charles Darwin and the theory of evolution, not that he believed it.
Others have noted many misconceptions that advocates of creation-science have fed their readers. One of these is that they will argue that scientists accept certain theories and views (such as evolutionary theory and an old universe) because they are somehow hostile to God and the Bible. They also argue that scientists reject creation-science because of similar attitudes. However, these are false. They reject creation-science because it doesn’t offer testable and falsifiable hypotheses, and as such cannot be considered a viable science.
1. Gish, D. 1979. Evolution? The Fossils Say No! p. 40.
2. National Academy of Sciences. 2008. Science, Evolution, and Creationism.
3. Haarsma, L. 2010. God, Evolution, and Design. p. 168.
4. Swift, A. 2017. In US, Belief in Creationist View of Humans at New Low. Available.
5. The Huffington Post. 2012. Believe In Evolution: Canadians More Likely Than Americans To Endorse Evolution. Available.
6. Ruse, M. 1982. Creation-Science is Not Science. p. 38.
7. Aron, R. 2016. Foundational Falsehoods of Creationism. p. 182.
8. Bates, S. 2006. “Archbishop: stop teaching creationism.” Available.
9. NSTA. Ibid.
10. Branch, G. 2010. American Academy of Religion on teaching creationism. Available.
11. National Academy of Sciences. 2008. Ibid. p. 10,
12. NAS. 2008. Ibid. p. 43.
13. Ruse, M. 1982. Ibid. p. 43.
14. Ruse, M. 1982. Ibid. p. 43-44.
15. Parker, G.. 1980. “Creation, Selection, and Variation,” in Acts & Facts. p. 144.
16. Lewontin, R. 1997. Billions and Billions of Demons. Available. | 0.823093 | 3.156278 |
ဖွံ့ဖြိုးတိုးတက်မှု၏လုပ်ထုံးလုပ်နည်းတခု exoplanets? NASA’s Hubble Area Tlescope could have recently found just such a thing– an unusual space in a massive protoplanetary disk of gas and dust turning around the red dwarf star TW Hydrae.
“TW Hydrae is located about 176 light-years away in the constellation Hydra ‚Äî the Sea Serpent. The only plausible explanation ‚Äî yet put forward ‚Äî for the gap in the protoplanetary disc that surrounds the star is that it is the result of a growing planet that is gravitationally gathering up much of the material that would otherwise be there. Of course such a planet has yet to be observed, and there are other possibilities.
Something to note, the distance between the gap and the parent star is rather large ‚ 7.5 ဘီလီယံအထိမိုင်. If the proposed planet was within our solar system that would put it at about two times the distance from the Sun that Pluto is quite a distance.
The location of the proposed planet seems strange though, to those in field ‚ challenging most popular theories on how planets form. The most popular theory claims that over a period of tens of millions of years that the material of a protoplanetary disc slowly aggregates concentrating the dust, rocks, and gas, of the disc into a proto planet. TW Hydrae and its newly proposed planet don‚Äôt match up with this theory though ‚the star system is only 8 million years old. There has not been enough time for a planet to grow through the slow accumulation of smaller debris. တကယ်တော့, a planet at 7.5 billion miles from its star would take more than 200 times longer to form than Jupiter did at its distance from the Sun because of its much slower orbital speed and a deficiency of material in the disk”. အရင်းအမြစ်: Planetsave
When I initially saw the space structure, it simply popped out like that, Debes clarifies. The truth that we see the space at every wavelength informs you that it’s a structural attribute rather than a critical artifact or an attribute of how the dust scatters light. | 0.850621 | 3.504714 |
MIT report researchers led by Alessandra Babuscia have developed a new design of antenna for small satellites known as CubeSats.
Due the their small size CubeSats have been restricted to small monopole or dipole antennas. Such low gain omni-directional antennas have restricted CubeSats to Low Earth Orbits (LEO) using lower data rates than would be possible with a large dish antenna.
The MIT team, led by Alessandra Babuscia, is part of the research group of radio amateur Professor Sara Seager KB1WTW and also includes graduate students Mary Knapp KB1WUA, Benjamin Corbin, and Mark Van de Loo from MIT, and Rebecca Jensen-Clem from the California Institute of Technology.
The new inflatable antenna developed by Alessandra Babuscia and her team may significantly increase the communication range of these small satellites, enabling them to travel much farther in the solar system: The team has built and tested an inflatable antenna that can fold into a compact space and inflate when in orbit.
It is claimed the distance that can be covered by a satellite with an inflatable antenna is seven times farther than that of existing CubeSat communications.
“With this antenna you could transmit from the moon, and even farther than that,” says Alessandra Babuscia, who led the research as a postdoc at MIT. “This antenna is one of the cheapest and most economical solutions to the problem of communications.”
An inflatable antenna is not a new idea. In fact, previous experiments in space have successfully tested such designs, though mostly for large satellites: To inflate these bulkier antennas, engineers install a system of pressure valves to fill them with air once in space — heavy, cumbersome equipment that would not fit within a CubeSat’s limited real estate.
Babuscia raises another concern: As small satellites are often launched as secondary payloads aboard rockets containing other scientific missions, a satellite loaded with pressure valves may backfire, with explosive consequences, jeopardizing everything on board. This is all the more reason, she says, to find a new inflation mechanism.
The team landed on a lighter, safer solution, based on sublimating powder, a chemical compound that transforms from a solid powder to a gas when exposed to low pressure.
“It’s almost like magic,” Babuscia explains. “Once you are in space, the difference in pressure triggers a chemical reaction that makes the powder sublimate from the solid state to the gas state, and that inflates the antenna.”
Testing an inflating idea
Babuscia and her colleagues built two prototype antennas, each a meter wide, out of Mylar; one resembled a cone and the other a cylinder when inflated. They determined an optimal folding configuration for each design, and packed each antenna into a 10-cubic-centimeter space within a CubeSat, along with a few grams of benzoic acid, a type of sublimating powder. The team tested each antenna’s inflation in a vacuum chamber at MIT, lowering the pressure to just above that experienced in space. In response, the powder converted to a gas, inflating both antennas to the desired shape.
The group also tested each antenna’s electromagnetic properties — an indication of how well an antenna can transmit data. In radiation simulations of both the conical and cylindrical designs, the researchers observed that the cylindrical antenna performed slightly better, transmitting data 10 times faster, and seven times farther, than existing CubeSat antennas.
An antenna made of thin Mylar, while potentially powerful, can be vulnerable to passing detritus in space. Micrometeroids, for example, can puncture a balloon, causing leaks and affecting an antenna’s performance. But Babuscia says the use of sublimating powder can circumvent the problems caused by micrometeroid impacts. She explains that a sublimating powder will only create as much gas as needed to fully inflate an antenna, leaving residual powder to sublimate later, to compensate for any later leaks or punctures.
The group tested this theory in a coarse simulation, modeling the inflatable antenna’s behavior with different frequency of impacts to assess how much of an antenna’s surface may be punctured and how much air may leak out without compromising its performance. The researchers found that with the right sublimating powder, the lifetime of a CubeSat’s inflatable antenna may be a few years, even if it is riddled with small holes.
Kar-Ming Cheung, an engineer specializing in space communications operations at NASA’s Jet Propulsion Laboratory (JPL), says the group’s design addresses today’s main limitations in CubeSat communications: size, weight and power.
“A directional antenna has been out of the question for CubeSats,” says Cheung, who was not involved in the research. “An inflatable antenna would enable orders of magnitude improvement in data return. This idea is very promising.”
Babuscia says future tests may involve creating tiny holes in a prototype and inflating it in a vacuum chamber to see how much powder would be required to keep the antenna inflated. She is now continuing to refine the antenna design at JPL.
“In the end, what’s going to make the success of CubeSat communications will be a lot of different ideas, and the ability of engineers to find the right solution for each mission,” Babuscia says. “So inflatable antennas could be for a spacecraft going by itself to an asteroid. For another problem, you’d need another solution. But all this research builds a set of options to allow these spacecraft, made directly by universities, to fly in deep space.”
Alessandra Babuscia is a Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT). She has worked on several satellite projects including CASTOR, ExoplanetSat, Rexis and TerSat.
Source – MIT press release | 0.825389 | 3.336903 |
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equally thiough the November one. On this account, the former star-showers are quite regular, while the latter vary in brilliancy through periods of 33£ years. (See p. 10.)
Relation Between Meteors And Comets.—The orbit of the November shower is found to be almost identical with that of the comet of 1866; while the August stream is in the track of the comet of 1862. It is a popular theory that these comets are only clusters of meteors crowded so closely together as to be visible by the reflected light of the sun. The single meteors are too small to be seen, except when they plunge into the earth's atmosphere and take fire. On the other hand, Herschel thinks that meteors are the dissipated parts of comets torn into shreds by the sun's attraction.
Radiant Point.—A star (n) in the blade of the sickle is the point from which the stars in the November shower seem to radiate, while one in Perseus (7) is the radiant point of the August shower. In the shower of 1866, two observers, who counted the falling stars at the rate of 2,500 per hour, saw only five whose paths, if traced back, would not meet in Leo.
Meteorological Effect.—The temperature of August and November is said to be considerably increased by this ring of meteoric bodies, which prevents the heat of the earth from radiating into space. A corresponding decrease of temperature in February and May is caused by the stream or ring of meteors coming between the sun and earth.
Height.—Herschel estimates the average height of shooting stars above the earth to be 73 miles at their appearance and 52 at their disappearance.
Weight.—Prof. Harkness estimates that the average weight of shooting stars does not differ much from one grain.
We come now to notice a class of bodies the most fascinating, perhaps, of any in astronomy. The suddenness with which comets flame out in the sky, the enormous dimensions of their fiery trains, the swiftness of their flight, the strange and mysterious forms they assume, their departure as unheralded as their advent—all seem to bid defiance to law, and partake only of the marvellous. Superstitious fears have always been excited by their appearance, and they have been looked upon in every age as
"Threatening the world with famine, plague, and war;.
Thus the comet of 43 B. c, which appeared jast after the assassination of Julius Csesar, was looked upon by the Bomans as a celestial chariot sent to convey his soul heavenward. An old English writet observes: "Cometes signifie corruptions of the ayre. They are signs of earthquakes, of warres, of changyng kyngedomes, great dearthe of corn, yea, a common death of man and beast." Another remarks: "Experience is an eminent evidence that a comet, like a sword, portendeth war; and a hairy comet, or a comet with a beard, denoteth the death of kings, as if God and nature intended by comets to ring the knells of princes, esteeming bells in churches upon earth not sacred enough for such illustrious and eminent performances."
Description.—The term comet signifies a hairy body. A comet consists usually of three parts;—the nucleus, a bright point in the centre of the head; the
coma (hair), the cloud-like mass surrounding the nucleus; and the tail, a luminous train extending generally in a direction from the sun. There are comets without the tail, and others with several, while some are deprived of even the nucleus. These last consist merely of a fleecy mass, known to be comets from their orbits and rapid motion. Comets are not confined, like the planets, to the limits of the zodiac, but appear in every quarter of the heavens, and move in every conceivable direction. When first seen, the comet resembles a faint spot of light upon the dark background of the sky: as it approaches the sun the brightness increases, and the tail begins to show itself. Generally it is brightest near perihelion, and gradually fades away as it recedes, until it is finally lost, even to the telescope.
The Time Of The Greatest Brilliancy depends somewhat on the position of the earth. If, as represented in the figure, the earth is at a when the comet, moving toward perihelion, is at r, the comet will appear more distinct than when it is more distant at s, although at the latter point it is really brighter. If, however, the earth is at c or b at the time of perihelion, the comet would be much more conspicuous. Again, if the earth is passing from a to b during the time the comet is near the sun, it will appear less brilliant than if it were moving from c to d, as we should then be much nearer it during its greatest illumination.
Number Of Comets.—Kepler remarks that there are as many "comets in the heavens as fish in the sea." Arago has estimated that there are 17,500,000 within the solar system, basing his calculations on the number known to exist between the sun and Mercury. Of this vast number, few are visible to the naked eye, and a still less number attract observation, owing to their inferior size and brilliancy. Many are doubtless lost to our sight by being above the horizon in the daytime. Seneca mentions that during a total solar eclipse, a large and splendid comet sud denly made its appearance near the sun.
Orbits Of The Comets.—Comets form a part of the solar system, and are subject to the laws of gravitation. Like the planets, they revolve around the sun, but they differ in the form of their orbits. While the planets move in paths varying but little from circular, and thus never depart so far from the sun as to be invisible to us, the comets travel in extremely elongated (flattened) ellipses, so that they can be observed by us only through a very small portion of their paths. In Fig. 67 are represented the three general classes of their orbits. A comet travelling along an elliptical orbit, though it may pass far from the sun, will yet return within a fixed time; one pursuing either a parabolic or hyperbolic curve cannot return, as the two sides separate from each other more and more. Many of the comets of the first class have been calculated, and they have repeatedly visited our portion of the heavens; while those of the other classes, having once formed part of our system, go away forever, seeking perhaps in the far-off space another sun, which in turn they will abandon as they have our own. | 0.865741 | 3.780538 |
Thursday, October 4, 2018
NGC 1898: GLOBULAR CLUSTER IN THE LARGE MAGELLANIC CLOUD Image Credit: ESA/Hubble & NASA
Jewels don't shine this bright -- only stars do. And almost every spot in this glittering jewel-box of an image from the Hubble Space Telescope is a star. Now some stars are more red than our Sun, and some more blue -- but all of them are much farther away. Although it takes light about 8 minutes to reach Earth from the Sun, NGC 1898 is so far away that it takes light about 160,000 years to get here. This huge ball of stars, NGC 1898, is called a globular cluster and resides in the central bar of the Large Magellanic Cloud (LMC) -- a satellite galaxy of our large Milky Way Galaxy. The featured multi-colored image includes light from the infrared to the ultraviolet and was taken to help determine if the stars of NGC 1898 all formed at the same time, or at different times. There are increasing indications that most globular clusters formed stars in stages, and that, in particular, stars from NGC 1898 formed shortly after ancient encounters with the Small Magellanic Cloud (SMC) and our Milky Way Galaxy. | 0.818991 | 3.224082 |
Paleoclimatologist studies sea levels in a desert
Exactly how much did the sea level rise three million years ago? Okay. Probably not a question you’ve asked yourself lately. But the question and, more importantly, its answer are significant. They will help scientists understand how fast and how high our current sea levels are likely to rise as today’s global warming trend melts the remaining ice sheets in Greenland and Antarctica.
Fortunately, there are researchers wrestling with the problem. Chief among them is Maureen Raymo, a paleoclimatologist at Boston University. Raymo heads a multidisciplinary team that is spending its second summer digging for evidence in the desert of Western Australia.
Raymo is drawn to really big questions, a really good thing considering her line of work. In order to understand the connection between Australia’s prehistoric sea level and today’s climate conundrum, you have to be able to think on a grand geologic and planetary scale.
It turns out that global temperatures fluctuated long before humans began adding heat-trapping gases to the atmosphere. The fluctuations were the result of subtle, recurring shifts in the Earth’s orbit as it travels around the sun.
The tilt of the planet varies predictably on a 41,000-year cycle. More tilt means warmer summers and colder winters at high latitudes; less tilt means cooler summers and milder winters. Scientists believe this 41,000-year variation (known as the Milankovitch cycle), along with other variables — like the shape of Earth’s orbit and the seasonal timing of when Earth is closest to the sun — have influenced the advance and retreat of glaciers and thus the onset of ice ages as more or less solar radiation reaches Earth at mid-to-high latitudes.
Such observations from the complex field of orbital dynamics have helped scientists like Raymo identify the cyclic changes in the Earth’s climate. But these “orbital forcings” are only a piece of the climate puzzle. The Earth’s geologic history also plays a role.
Three million years ago, during what is known as the mid-Pliocene climate optimum, Earth was a much warmer place. In fact, this period marked the most recent time during which the climate was consistently warmer than it is today for an extended period. During the mid-Pliocene climate optimum, global temperatures were as much as 5.4 degrees F above today’s averages. As a graduate student, Raymo proposed that this warmth was due to higher levels of carbon dioxide in the atmosphere at the time, a hypothesis that is still being tested today.
Scientists are not sure how high the sea level was during the mid-Pliocene climate optimum. Some past research suggests that it was just 15 feet higher than it is today; other research puts it as much as 100 feet higher. Raymo hopes to significantly narrow this gap. “If we can determine exactly where the shoreline was three million years ago,” she says, “we can tell a lot about how much ice remained in Greenland and Antarctica during this warm period.”
To map the ancient shoreline, Raymo and her team work their way inland from the Australian coast in search of fossilized coral reefs and other evidence that the land was once covered by ocean. “Each time you add a data point,” Raymo says, “you help to calibrate existing climate models in an important way and build a broader knowledge base for future experiments.”
Raymo is quick to add that uncertainty about a specific question such as the maximum sea level in the Pliocene Epoch should not be equated with uncertainty about today’s overall global warming trend. Climate-change skeptics who jump on uncertainties to dispute global warming, “completely miss the point,” says Raymo. “Science is always evolving intellectually, processing and incorporating the latest information. Scientists always want more knowledge. They always say ‘I want to try to test out that new idea.'”
“Even so,” Raymo says, “everything I’ve learned about the dynamism of the planet’s climate places me, like most all of my colleagues, strongly in the camp that says we need to take preventive action to keep the planet from warming further. I am extremely concerned that we’ve made such large changes in the composition of our atmosphere with so little understanding of the consequences. The path we are on is completely anomalous to anything that has gone before.”
Paleoclimatologists like Raymo focus on vast stretches of geological time, studying variations in the earth’s climate over the course of the planet’s history, gleaning evidence from a variety of sources to track which parts of the planet were once covered by glaciers or oceans. They see geologic evidence of glaciers in shifts of the terrain and in the rocks and other material the glaciers left behind; they find chemical evidence of oceans in variations in the ratios of isotopes in sedimentary rocks.
The tricky part, of course, is to figure out how to use the hard evidence available today to draw conclusions about past climate. It is a part of her job that Raymo particularly enjoys. “I love thinking ‘How does the Earth work?'” she says. “I have always felt a natural ability to think about the planet, almost as though I were looking down on it from above.”
This kind of big picture thinking runs in Raymo’s family. Her father, Chet Raymo, is a science writer well known for his musings on grand-scale topics in the natural world. But when asked how she got interested in science, Raymo credits Jacques Cousteau. At age seven, she was captivated by one of the French undersea explorer’s television programs. “From then on I decided I wanted to be an oceanographer,” she says. That passion stayed with her all the way to college, when she was seduced anew by the cutting-edge climate research of geologists John Imbrie and William Ruddiman, who became her mentors.
In her research, Raymo tackles many aspects of paleoclimate and orbital forcings. In 2006, she hypothesized, in the journal Science, about why the 41,000 year Milankovitch cycle appears less pronounced over the past 500,000 years. “It was a question that I had literally been thinking about since graduate school some two decades earlier,” she says. No one knows the answer yet. But Raymo’s theory — that ice growth at one pole occurs simultaneously with ice decay at the other, thereby canceling out the signal of ice volume change in global climate records — has sparked a great deal of new research and debate. If she’s right, then earth’s climate is even more dynamic and complex, especially in the area of the Antarctic ice sheet.
While orbital forcings offer a fascinating window into the historical mechanisms of climate variation, Raymo emphasizes that they are overshadowed today by human-driven effects on the climate. “People sometimes ask me: ‘When will the next ice age be?'” she says. “The answer is that I’m pretty sure we have already prevented it. Like it or not, we are now the main drivers of the climate, even though so far we’ve been doing it completely by accident.”
The Union of Concerned Scientists is currently leading a campaign to elevate the voices of climate scientists and educate the public about the overwhelming scientific evidence for human-caused global warming. Learn how you can get involved at www.ucsusa.org/evidence. | 0.866241 | 3.562591 |
You don’t have to look far to find outlandish theories on the nature of the cosmos and human consciousness.
These days, notions once relegated to science fiction are finding their way into esoteric academic journals, and from there, into mainstream discourse.
The newest symphony of mind jazz being broadcast across the Internet posits new ideas about the embattled theory of “panpsychism,” or the belief that mind is a fundamental property of the physical universe and is imbued into all states of matter.
A new paper, published by physicist Gregory Matloff, has brought the idea back into scientific discussions, promising experimental tests that could “validate or falsify” the concept of a ubiquitous “proto-consciousness field.”
Matloff also pushes the controversial idea of volitional stars, suggesting there is actually evidence that stars control their own galactic paths.
As absurd as the theory sounds, it has several prominent adherents, including British theoretical physicist Sir Roger Penrose, who introduced panpsychism three decades ago.
Penrose believed consciousness arises from the properties of quantum entanglement.
He and anesthesiologist Stuart Hameroff authored the Orchestrated Objective Reduction (Orch-OR) hypothesis, which asserts, among other things, that consciousness results from quantum vibrations inside microtubules.
In 2006, German physicist Bernard Haisch took the idea further and proposed that consciousness arises within a “quantum vacuum” any time there is a significantly advanced system through which energy flows.
Neuroscientist Christof Koch, another proponent of panpsychism, approaches it from a different angle, using integrated information theory to argue that consciousness is not unique to biological organisms.
“The only dominant theory we have of consciousness says that it is associated with complexity — with a system’s ability to act upon its own state and determine its own fate,” Koch argues.
“Theory states that it could go down to very simple systems. In principle, some purely physical systems that are not biological or organic may also be conscious.”
Matloff and other scientists are moving the argument into a new phase: experimentation. Matloff intends to study the behavior of stars, specifically analyzing an anomaly in stellar motion known as Paranego’s Discontinuity.
Matloff wants to know why certain cooler stars appear to emit jets of energy pointed in one direction, a characteristic that seems oddly and inexplicably ubiquitous in the galaxy.
In 2018, he plans to use results from the Gaia star-mapping space telescope to show that the anomaly may be a willful stellar action.
Meanwhile, as Matloff studies cosmic activity on the grandest scale, Koch approaches the experimental phase of the theory using brain-impaired patients.
He wants to know if their information responses match underlying neurochemical foundations of consciousness.
He plans to test this by wiring the brains of mice together to see if their minds merge into a larger information system.
Panpsychism certainly has critics, as well. In an article for The Atlantic entitled “Why Panpsychism Is Probably Wrong,” Keith Frankish writes:
“Panpsychism gives consciousness a curious status. It places it at the very heart of every physical entity yet threatens to render it explanatorily idle.
“For the behavior of subatomic particles and the systems they constitute promises to be fully explained by physics and the other physical sciences.
“Panpsychism offers no distinctive predictions or explanations. It finds a place for consciousness in the physical world, but that place is a sort of limbo.”
The quote expresses a general sense that panpsychism oversimplifies the hard problem of consciousness in the universe, an opinion many scientists share.
However, Matloff, Penrose, and other proponents continue undertaking the job of venturing outside the margins of accepted science to try reconciling intractable contradictions and anomalies exposed by quantum theory.
By Jake Anderson, Guest author | 0.87146 | 3.393354 |
Assuming everything goes according to plan, NASA's Curiosity rover will touch down on the surface of Mars this Sunday, August 5th at 10:31 PDT. Curiosity travels in the cosmic wake of not only the pioneering landers and rovers that have made journeys to Mars before, but also the innumerable visionaries who showed us how we might get there —well before it was possible.
From 1952 until 1954, the weekly magazine Collier’s published a series of articles on space exploration spread out across eight issues. Several of the articles were written by Wernher von Braun, the former Third Reich rocket scientist who began working for the U.S. after WWII. The Collier's series is said to have inspired countless popular visions of space travel. This impact was in no small part due to the gorgeous, colorful illustrations done by Chesley Bonestell, Fred Freeman and Rolf Klep.
The last of the Collier's space-themed series was the April 30, 1954, issue that featured a cover showing the planet Mars and two headlines: "Can We Get to Mars?" and directly underneath: "Is There Life on Mars?" The article, "Can We Get to Mars?," by von Braun is a fascinating read that looks at everything from the impact of meteors on spacecraft to the stresses of living in cramped quarters during such a long journey. Even when astronauts finally arrived on Mars, they'd still be subjected to claustrophobic living conditions, as you can see from the illustration above by Fred Freeman. The astronauts—who in this illustration have landed on an icy Martian pole—live in inflatable, pressurized spheres that are mounted on tractors.
Von Braun’s story in the 1954 issue explained that he didn’t believe he’d see a man on Mars within his lifetime. In fact, von Braun believed that it would likely be 100 years before a human foot would touch Martian soil. But there was absolutely no doubt that we would get there.
Will man ever go to Mars? I am sure he will—but it will be a century or more before he’s ready. In that time scientists and engineers will learn more about the physical and mental rigors of interplanetary flight—and about the unknown dangers of life on another planet. Some of that information may become available within the next 25 years or so, through the erection of a space station above the earth (where telescope viewings will not be blurred by the earth’s atmosphere) and through the subsequent exploration of the moon, as described in previous issues of Collier’s.
But unlike NASA's current Mars mission, von Braun's vision for travel included humans rather than simply rovers. As Erik Conway, historian at the Jet Propulsion Laboratory explains, “There have also always been—since at least Wernher von Braun—people proposing expeditions to Mars with humans, with astronauts. Von Braun’s idea was to send a flotilla of spacecraft, not just one. As you’ve seen in the Collier’s magazines and so on, he was a big promoter of that. And that affected how the American public saw Mars as well. So it was being promoted as a future abode of life for us humans—and it still is in a lot of the enthusiast literature. That hasn’t changed. It’s just the funding isn’t there to actually accomplish it.”
The funding may not be there today, but the space interest revival we're currently seeing under the unofficial leadership of astrophysicist and media personality Neil deGrasse Tyson could very well help change that. Look for a reboot of the late Carl Sagan's 1980 mini-series Cosmos in 2013, starring Tyson.
For now, we'll just have to settle for the exciting discoveries that (hopefully) will be beaming down from Mars next week and some good old fashioned space art. Below are samples of the amazing illustrations from the April 30, 1954 issue of Collier's by Bonestell, Freeman and Klep.
Wernher von Braun imagined that spacecraft would be assembled 1,000 miles from earth near a wheel-shaped space station.
The cropped illustration above, by Chesley Bonestell shows four of the ten spacecraft von Braun imagined would undertake the journey.
The first landing party takes off for Mars. Two other landing planes will wait until runway is prepared for them, and the remaining seven ships will stay in 600-mile orbit. Arms on cargo ships hold screenlike dish antenna (for communication), trough-shaped solar mirrors (for power).
The illustration above by Rolf Klep explains how the earth and Mars must be positioned in order for a successful flight to occur.
This illustration above of astronauts preparing for their return flight was done by Chesley Bonestell.
After 15 month exploration, the Mars expedition prepares for return flight to earth. Two landing planes are set on tails, with wings and landing gear removed. They will rocket back to the 600-mile orbit on first leg of journey
This illustration, by Fred Freeman shows all ten spacecraft as they travel to Mars.
Illustration shows how the landing planes are assembled in 600-mile Martian orbit. Pointed noses are removed from three of 10 ships that made trip from earth; wings and landing gear are fitted to them. Cutaway of plane in the foreground shows personnel, tractors in ship
This post originally appeared at Smithsonian.com. | 0.846952 | 3.212476 |
Don Machholz of Colfax, CA found his 11th comet on the morning of Tuesday, March 23rd. What sets Don’s 11 discoveries apart from the other comets found recently is the way it was found. Nowadays comets are found by computers analyzing thousands of digital images. Only after the computers have sorted through the data is there human intervention to confirm that the object being flagged as a comet is really a comet. Don, on the other hand, has found all 11 of his comets the old-fashioned way. With no help from computers or digital cameras, Don finds his comet by peering through his telescope and identifying faint fuzzies that shouldn’t be there. In fact, it is the first visual discovery of a comet since late 2006.
Comet C/2010 F4 (Machholz) is currently 11th magnitude. At this brightness, only observers with moderate-sized telescopes under dark skies will see it. Though the orbit is still somewhat uncertain, the comet appears to reach perihelion in early April at a distance of ~0.6 AU from the Sun. Unfortunately, it will not get much brighter. In fact, seeing it will only get more difficult as the comet moves closer to the Sun. Its increasing proximity to the Sun and the bright Moon now located in the morning sky means even advanced observers will have a hard time seeing it after a few days. It is possible the comet may only be observed for a week or so and then lost for the ages.
The image above shows the orbit of the comet. With an inclination of ~90 degrees, its orbit is perpendicular to the orbits of the planets which is not unusual for a long-period comet. The big question is how was this comet missed by all of the professional asteroid/comet surveys. Nowadays most comets are found while very faint (17-19th magnitude) and a few years before perihelion. This comet probably escaped detection because it was located near the Milky Way for the past year. The Milky Way is so full of stars that the current crop of asteroid/comet surveys have a difficult time finding any objects there. As a result, many surveys avoid the Milky Way all together.
Congrats to Don Machholz! And thanks for showing us that persistence (he hunted for 607 hours since his last find in 2004) and old-fashioned comet hunting can still pay off in this era of computers and automation. | 0.804923 | 3.556409 |
Research Article | Open Access
Electromagnetic Analysis and Experimental Validation of the LOFAR Radiation Patterns
Low-frequency (<300 MHz) aperture array systems are one of the new trends in modern radio astronomy. Among the challenges they pose, the instrumental calibration is a key aspect requiring an accurate and reliable model of each element of such electrically large array. A full-wave electromagnetic analysis has been carried out for the lower frequency (30–80 MHz) array of the low frequency array (LOFAR) radio telescope taking into account the presence of soil ground, the mutual coupling between the antennas and the relevant receiver impedance loading effects. The impact of mutual coupling effects on the embedded element and array patterns is assessed for two subarray configurations with different degrees of sparseness. A simplistic array factor approach has been implemented as well to determine the accuracy in the antenna pattern evaluation with respect to the full-wave approach. Finally, results from an experimental campaign conducted by means of a micro hexacopter system show the reliability of the developed array numerical model.
Since approximately two decades, radio astronomers are investing significant resources in studying and developing aperture array systems for radio astronomical observations. Aperture array technology exploits digital beamforming to steer the array beam towards the celestial sources. In order to have enough collecting area and high angular resolution, the array is composed of a multitude of small antennas spread over large distances. For instance, the low frequency aperture array (LFAA) subsystem of the square kilometre array (SKA) , the largest radio telescope ever built, will be composed of more than 130.000 antennas operating between 50 and 350 MHz. ASTRON, the Netherlands Institute for Radio Astronomy, inaugurated the low frequency array (LOFAR) in 2010 . LOFAR is a pathfinder for the SKA and is nowadays a world-class facility for astronomical research, with seven partner countries in Europe. It consists of 38 stations spread in the Netherlands and 13 deployed in other European countries. All stations include two different antenna types (see Figure 1): high-band antennas (HBA) working in the 120–240 MHz frequency range and low band antennas (LBA) operating between 30 and 80 MHz. The aperture array characteristics of the LBA system are conceptually similar to the LFAA planned for SKA. Therefore, the LBA array is widely used as an appropriate test bed to acquire experience in view of the SKA. In this perspective, the modelling activity on the LBA array, which is the focus of this paper, provides useful guidance for what can be expected for SKA.
The adopted antenna distribution for LBA array is a sparse random configuration of 96 antennas divided in two different subarrays called LBA-outer and LBA-inner, the former being sparser than the latter. The randomized positions of the antennas in both LBA subarrays not only assure a smoothness of the station pattern without grating lobes [3, 4] but also cause a significant diversity in the responses of each individual antenna due to mutual coupling effects. As a result, the array calibration becomes quite challenging as every antenna response needs to be evaluated individually . This is further complicated by the strong dependence of the embedded patterns on the receiver impedance, especially at the resonance frequency as discussed in .
The current LOFAR data reduction pipeline assumes very simple and identical embedded-element patterns. Therefore, an accurate characterization of the antenna patterns by including the effect of soil ground, the mutual coupling effects, and the receiver impedance is expected to improve the quality of the astronomical data, especially for the LBA-inner array where the antenna coupling levels are higher. Fortunately, the availability of both powerful hardware resources and reliable computational electromagnetic tools nowadays make it possible to accurately simulate antenna patterns in a complex environment with a full-wave approach.
In this paper, we conduct a rigorous full-wave electromagnetic analysis of the LBA subarrays taking into account geometrical and electrical aspects of the arrays. Such results are compared to the present LOFAR calibration model (i.e., array factor multiplied by the isolated element pattern). The objective of this comparison is both to quantify the importance of the presented modelling approach and to assess its actual necessity in the sparse array scenario.
Furthermore, we validate the LBA array electromagnetic model using experimental data obtained during a measurement campaign performed in 2016 with an unmanned aerial vehicle (UAV) system described in . This campaign has been already successfully used to characterize the LBA-inner array near-field (NF) pattern . The novelty of this contribution is to show the agreement of the measured radiation patterns with the far-field (FF) numerical analysis.
The paper is organized as follows: the description of the LBA configuration and the model of a receiving array loaded by a receiver chain network are described in Sections 2 and 3, respectively. The numerical results for the LBA-inner and LBA-outer arrays are reported in Section 4 for the FF regime, whereas the measurement results obtained with the UAV system are compared to simulations in Section 5. Finally, Section 6 draws the conclusions.
2. Low-Band Antenna Configurations
Low-band antennas are arranged in randomly perturbed rings with exponentially increasing radii (see Figure 2). The LBA-inner array is composed of 46 dual-polarized antennas distributed within a 30 m circle (plus two outer antennas used for calibration purposes, not shown in Figure 2), while the LBA-outer array consists of 48 dual-polarized antennas distributed in an annulus with a 30 m inner diameter and a 85 m outer diameter.
The antennas of the two subarrays are distributed with a different degree of sparseness and of randomization. The array sparseness is defined on the basis of the ratio between the averaged spacing () and the wavelength (). A threshold level of separates a dense array regime () from a sparse array regime () . For each subarray, is evaluated as the mean of the distances between each antenna and the nearest antenna within the subarray. The average values and their standard deviation turn out to be 3.4 ± 0.6 m and 7.3 ± 1.9 m for LBA-inner and LBA-outer, respectively. The ratios for the two LBA subarrays within the operating frequency range are reported in Table 1 (the frequencies are chosen to match those used in the UAV measurement campaign). The ratios show that the LBA-inner array can be considered a dense array for the frequencies below 44 MHz, while it behaves as a sparse array for frequencies larger than 44 MHz; the LBA-outer array is instead a sparse array for all operating frequencies.
As far as randomization is concerned, the LBA-outer array can be considered fully randomized while the LBA-inner array shows some regular features for the central area as evident from Figure 2.
The two subarrays are composed of identical receiving elements that cover the 30–80 MHz operating frequency bandwidth. Each element consists of two perpendicular inverted V-shaped dipole antennas sensitive to two orthogonal linear polarizations and is placed on a metallic wire mesh ground plane of 3 × 3 m2. The two dipoles are oriented at 45° with respect to the cardinal directions. Two low-noise amplifiers (LNA), enclosed in the black package at the antenna feeding point (see Figure 1(b)), increase the received signal levels before they are transported to the station cabinets through two coaxial cables .
3. Modelling of the Receiving Array
Due to the nonreciprocity of the amplifiers connected to the antennas, the LBA array electromagnetic characterization is conducted in receiving mode; therefore, the formulation in this paper is presented accordingly. A -port equivalent Thévenin circuit is employed to represent the receiving array system.
For the equivalent circuit in Figure 3, the voltages at the terminations of the receivers can be described in matrix form. Using this formulation, the column vector in equation (1) contains the voltages at the terminations of the receivers and is described as follows: where is a diagonal matrix accounting for the impedance of the receivers (which are not coupled to each other), is the (full) array impedance matrix, and is a column vector with the open-circuit voltages at the antenna terminals. Since the antennas are embedded in an array, the array impedance matrix accounts for the mutual coupling between the elements.
It should be noted that and depend on the observation direction. However, for the sake of simplicity, the dependence on the direction coordinates will be understood throughout the formulation. The th component of the open-circuit voltage vector can be written as the scalar product between the incident electric field (arbitrary polarized) and the receiving antenna effective length :
Exploiting the reciprocity principle, the antenna effective length can be deduced from the radiation electric field emitted by each single antenna through the following formula : where is the distance from the reference center, is the propagation medium impedance, is the receiving wavelength, is the wavenumber, and is the excited current at the antenna terminals.
Finally, the voltage at the output of the receiver network () is obtained as a weighted superposition (beamforming) of the voltage induced at the terminations of the receiver devices : where is the transpose of the complex column vector composed of the weights. This vector takes into account the gains of the receivers, the calibration coefficients, and the phases assigned to each single antenna to steer the array beam towards a specific direction.
To summarize, the formulation reported here allows to characterize the element and array pattern in loaded conditions starting from (i) the open-circuits embedded element patterns, (ii) the array impedance matrix, and (iii) the impedances of the receivers.
4. EM Analysis of the LBA Subarrays
Results presented in this paper are based on simulated data in the FF regime using FEKO, a commercial full-wave electromagnetic software package. Both LBA subarray geometries have been simulated separately based on their actual geometry and neglecting possible mutual coupling between the two subarrays. This latter assumption is made to not significantly increase the simulation computational time and has been validated by the experimental verification discussed in Section 5.
Each dual-polarized element has been simulated using two discrete ports. The size introduced in Section 3 refers therefore to the total port number including both polarizations. A finite metallic grid under each element has been modelled by a 3 × 3 m2 solid rectangle of perfect electric conductor. Then, a semi-infinite dielectric layer (relative electric permittivity equal to 3 and conductivity equal to 0.01 S/m) is used to model the terrain.
The array impedance matrix has also been evaluated using FEKO. The LNA input impedances have been evaluated starting from the measured amplifier scattering parameters and considered identical for all elements: (16.2–j341.0) Ω, (5.6–j236.7) Ω, (17.0–j215.3) Ω, and (2.8–j137.2) Ω at the four frequencies, respectively.
In the following analysis, a unity incident plane wave with a linear polarization aligned to the copolar component of the ports oriented along the north-east direction is adopted. The embedded element patterns are evaluated as the voltages and they are referred to EEPs, while the resulting array beam patterns are evaluated as the voltage .
Besides the rigorous full-wave analysis, the antenna pattern has also been computed under mutual coupling-free conditions by modelling only one dual-polarized antenna above the finite metallic rectangle and the semi-infinite soil ground. This approach results in an isolated element pattern, indicated as IEP. In this simplified case, the array factor has been used to evaluate the resulting array beam.
In the following analysis, the linear differences between full-wave and simplified patterns are used to quantify the agreement between the two approaches. Such figure of merit allows to de-emphasize possible spikes present in correspondence of the nulls of the array patterns .
4.1. Coupling Coefficients Results
A simple characterization of the mutual coupling in an array can be obtained by the analysis of the scattering matrix of the array. The scattering matrix assumes that all antennas are closed with matched loads. Therefore, in order to take into account highly mismatched receiver impedances, a column vector introduced in (see equation (2) in that paper) is employed here. This vector represents the power waves reflected by -1 receivers connected to the passive antennas when a specific antenna is excited. This quantity can be used to evaluate the amount of coupling between different pairs of antennas.
Figure 4 shows the coupling coefficients between all possible pairs of antennas both for LBA-outer (red dots) and LBA-inner arrays (black dots). The coupling is given as a function of distance between the antennas and results in a decreasing curve with distance. The LBA-inner array being more compact than the LBA-outer array, the overall coupling for the first subarray is definitively higher than for the latter. A frequency dependence of the coupling level is also clearly visible, which is related to the antenna mismatch; in particular, at 57 MHz, the coupling level is higher than at other frequencies, since the antennas are better matched.
4.2. Discussion on the Element Patterns
The effects of mutual coupling on the FF embedded element patterns composing both the LBA-outer and LBA-inner subarrays are discussed in this subsection. Figures 5 and 6 show the patterns along the E-plane for the LBA-outer and LBA-inner configurations (polar angle between −60° and 60°), respectively. For each frequency and for each subarray, the results for the embedded element pattern analysis are organized in two panels. The upper panel shows a grey shading for the EEP distribution within one standard deviation, a black curve for the averaged EEPs (indicated as ) and a grey curve for the IEP. Due to the resonance matching properties of the LBA dipoles with their amplifiers (see ), the pattern absolute levels turn out to be significantly frequency dependent. Therefore, in order to give a clear picture at all frequencies of the EEPs and IEP behavior, the patterns have been normalized to their maxima.
The bottom panel shows two curves: one, indicated as std is the normalized standard deviation of the EEPs distribution, while the other, (IEP, ) is the difference between the isolated element pattern and the mean of the embedded element patterns. Both curves are computed on linear scales. The normalized standard deviation gives an idea of the level of diversity between the embedded element responses (which is related to the level of coupling and to the array irregularity), while the difference (IEP, ) represents how well the isolated antenna pattern can described as the average element response.
At 32, 44, and 70 MHz, the normalized standard deviation reported in Figure 5 shows that the variations between the LBA-outer embedded element patterns is so low that the shading turns out to be quite indiscernible from the curve over the whole considered observation angle range. This is clearly visible from the black curves in the bottom panels where the normalized standard deviation is almost constantly lower than 3%. These results can be attributed to the sparse configuration of LBA-outer elements, which mitigates the mutual coupling effects. At 57 MHz, the resonance phenomenon due to the loaded antenna system causes a magnification of the mutual coupling effect that is distinctly visible in Figure 5(c), where the normalized standard deviation increases to 5%.
Far from the resonance frequency, the and the IEP curves are almost completely superimposed on each other (see the grey curves in the bottom panels). This suggests that the mutual coupling effects are almost completely negligible in the LBA-outer array, and therefore, a simpler mutual coupling-free approach produces quite accurate results that differ less than 1% from the full-wave analysis. At 57 MHz, the difference doubles (see the bottom panel of Figure 5(c)) for the aforementioned reasons.
Unlike the LBA-outer array, the upper and bottom panels of Figure 6 show that for the LBA-inner array, the variations between the embedded patterns are more significant with a normalized standard deviation between 6% and 12% (at 32, 44, and 70 MHz) and reaching levels as high as 20% at 57 MHz. This larger difference between antennas can be attributed to a less-randomized antenna distribution and to a higher mutual coupling due to the closer spacing. The stronger coupling effects are also visible in the difference between and IEP curves even if with some peculiarities: at 32 MHz, the difference is comparable to the LBA-outer case (below 1%), while at the two central frequencies (44 and 57 MHz), it increases at 6%. However, the highest difference occurs at 70 MHz with 9% discrepancy.
4.3. Discussion on the Array Patterns
In this subsection, the embedded voltages evaluated above are summed together to produce the array patterns. These are computed by assuming that the weights in vector w in equation (4) for the ports aligned to the north-east direction are all unity. This equiphase feeding scheme produces a main beam pointing towards the zenith direction.
The simulated normalized array patterns are shown in Figures 7 and 8 along the E-plane (polar angle between −45° and 45°) for the LBA-outer and LBA-inner arrays, respectively. The corresponding array patterns computed by using the array factor approach is plotted as well. An additional panel shows the linear difference between the array patterns computed with the full-wave approach and the simplified one. The frequencies are again 32, 44, 57, and 70 MHz.
The discrepancy of the simplified approach from the rigorous full-wave analysis of the LBA-inner and LBA-outer arrays is highlighted in Table 2, which reports the maxima of the linear differences for the array patterns. It also includes the case of the array pattern steered to 25° zenith angle to evaluate the differences between the two approaches in an off-axis condition.
The randomized distribution ensures that grating lobes are absent, as expected, and side lobes are always below −12 dB from the array peak. The overall agreement for the LBA-outer array (Figure 7) confirms the low mutual coupling already seen for the embedded patterns. The differences between the two curves do not exceed the error of 1% (corresponding to 0.1 dB) at 32 and 44 MHz, whereas the difference increases to 1.4% at 70 MHz and around 2% at 57 MHz.
On the other hand, the LBA-inner array patterns (Figure 8) indicate that the isolated antenna pattern produces less accurate results reaching difference up to 3% (corresponding to 0.25 dB) within the visible observation angle region at 32 and 44 MHz. At 57 and 70 MHz, such discrepancy increases to 7% and 5%, respectively.
In the LBA-outer array case, for every frequency, the accuracy levels for the array patterns are very similar to those computed for the embedded patterns. Vice-versa, in the LBA-inner array, it is not possible to identify a correspondence between embedded and array accuracies. This is likely due to the stronger mutual coupling and the random combination of the embedded patterns.
5. Experimental Validation of the LBA Subarrays EM Models
An intensive experimental characterization of a LOFAR station (CS302, located in Exloo, the Netherlands) was performed in 2016 by means of an UAV-mounted probe [6, 8]. This technology has been employed successfully to validate the electromagnetic model of several low-frequency aperture array systems [15, 16]. Both a radio frequency transmitter connected to a 2 m long dipole and a differential global positioning system (GPS) were installed on the UAV. Such a flying test source performed several flights above the LOFAR telescope.
The experimental data recorded for the LBA-inner array was for only 40 of the 46 antennas composing the array; for this reason, the EM model used for the validation simulated all 46 antennas but left out (weight equal to zero) the missing antennas in the array pattern computation. As far as the LBA-outer array is concerned, all 48 elements were acquired during the campaign. For both subarrays, the ports aligned along the north-east direction have been considered. A flight along the north-east direction with a constant height of 300 m has been selected for the LBA-inner array, while the only available UAV flight for the LBA-outer array was performed at a height of 100 m.
It is worthwhile emphasizing that for the LBA-inner array, the UAV trajectory is quite close to the FF region boundary (being 265 and 420 m at 44 and 70 MHz, respectively). On the contrary, the UAV was not able to reach the FF region of the LBA-outer array, the FF boundary being equal to 2100 m (44 MHz) and 3300 m (70 MHz).
The selected beamforming strategy to combine the measured embedded element patterns consists in the phase and amplitude equalization with the UAV located above the central element of the array . Furthermore, the measured array patterns have been deconvolved, using the Friis formula, for the distance between the array and the UAV and for the transmitting dipole pattern (see for more details on the deconvolution procedure). According to the procedure applied for the experimental data, the numerical embedded patterns have been equalized at the zenith direction.
Figure 9 shows the normalized simulated and measured array patterns between observation angles of −45° and + 45° in the top panels and the linear differences in the bottom panels. The array patterns in Figure 9 refer to the LBA-inner array (left column) and the LBA-outer array (right column). Patterns are plotted in the E-plane at the measured frequencies of 44, 57, and 70 MHz.
At all frequencies, the measured and simulated LBA-inner array patterns show an excellent agreement. At 44 and 70 MHz, the maximum of the differences is 1.5% and 2% (Figures 9(a) and 9(e)), respectively, whereas at 57 MHz, such difference reaches 4% (Figure 9(c)). The frequency of 57 MHz turns out to be the least accurate, which is due to the stronger dependence on the receiver impedance, and therefore, some inaccuracies in that value affect the simulated pattern response. The dependence of the simulated patterns from the receiver impedance is further discussed at the end of this section.
A larger disagreement is present for the LBA-outer array where the maximum of the difference grows up to 10%–20% depending on the frequency (Figures 9(b), 9(d), and 9(f)). Such discrepancy between numerical and experimental analysis is due, as mentioned before, to the fact that the experimental patterns are measured very far from the FF region. This results confirms that for measurements performed in the NF region, the approach proposed in with the simulations computed in NF is the correct strategy for the comparison.
Figure 9(c) suggests that an important condition to compare successfully the experimental and the simulated FF patterns, at the resonance frequency, is to consider the antennas loaded with the correct receiver impedance. In this respect, Figure 10(a) shows, for the LBA-inner array, the measured pattern at 57 MHz compared to two simulated patterns obtained with different LNA impedance values: standard 50 Ω and measured impedance (see Section 4). The simulated patterns turn out to be quite sensitive to the receiver impedance. Furthermore, the bottom panel of Figure 10(a) highlights that a better agreement with the measured data is reached when the antennas are simulated with the measured impedance (averaged difference 1.4%) rather than with 50 Ω (2%). On the contrary, at 70 MHz the antenna-receiver system is far from the resonance condition, and the two simulated array patterns almost overlap with an averaged discrepancy of only 0.6% (see Figure 10(b)).
A deep investigation of the array performance including mutual coupling and receiver impedance is an important step to improve the observation capabilities of an aperture array system. The rigorous approach defined in this contribution for LOFAR can be considered a valid guideline that could be applied to other aperture array systems, such as the LFAA stations of SKA.
The proven reliability of the electromagnetic model permits to investigate and quantify the mutual coupling effect on the overall performance for two array configurations featuring different levels of sparseness. The mutual coupling has been evaluated by comparing the antenna patterns computed by a rigorous analysis and a simplified one based on an isolated antenna analysis.
Except for the resonance frequency, the LBA-outer array analysis shows quite a negligible difference between a mutual coupling-free approach and a full-wave analysis. As expected, the LBA-inner array is characterized by stronger mutual coupling between the antennas, which compromises the accuracy level reachable by using the isolated approach. Therefore, depending on the scientific requirements of the astronomical observation, the simplified approach may be inappropriate to model the antenna responses.
Finally, some measured results performed with a UAV system show an excellent agreement for the LBA-inner array with the numerical results computed in realistic electrical and geometrical conditions. On the other hand, a similar comparison for the LBA-outer array suffers for the UAV flying in the NF region of the array.
The raw data and plots supporting the conclusions of the study are available on demand from the corresponding author.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
This work was supported in part by the National Institute for Astrophysics under program TECNO INAF 2014 and in part by the Netherlands Organization for Scientific Research.
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- G. Pupillo, G. Naldi, G. Bianchi et al., “Medicina array demonstrator: calibration and radiation pattern characterization using a UAV-mounted radio-frequency source,” Experimental Astronomy, vol. 39, no. 2, pp. 405–421, 2015.
- P. Bolli, G. Pupillo, G. Virone et al., “From MAD to SAD: the Italian experience for the LOW-frequency aperture array of SKA1-LOW,” Radio Science, vol. 51, no. 3, pp. 160–175, 2016.
Copyright © 2019 Paola Di Ninni et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. | 0.807698 | 3.563381 |
By Megan Watzke
In everyday life, ultraviolet, or UV, light earns a bad reputation for being responsible for sunburns and other harmful effects on humans. However, research suggests that UV light may have played a critical role in the emergence of life on Earth and could be a key for where to look for life elsewhere in the Universe.
A new study by Sukrit Ranjan of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and colleagues suggests that red dwarf star might not emit enough UV light to kick-start the biological processes most familiar to our planet. For example, certain levels of UV might be necessary for the formation of ribonucleic acid, a molecule necessary for all forms of known life.
“It would be like having a pile of wood and kindling and wanting to light a fire, but not having a match,” said Ranjan. “Our research shows that the right amount of UV light might be one of the matches that gets life as we know it to ignite.”
This research is focused on the study of red dwarf stars, which are smaller and less massive than the Sun, and the planets that orbit them. Recently, several planetary systems with potential habitable zones, where liquid water could exist, have been discovered around red dwarfs including Proxima Centauri, TRAPPIST-1, and LHS 1140.
Using computer models and the known properties of red dwarfs, the authors estimate that the surface of rocky planets in the potentially habitable zones around red dwarfs would experience 100 to 1,000 times less of the ultraviolet light that may be important to the emergence of life than the young Earth would have. Chemistry that depends on UV light might shut down at such low levels, and even if it does proceed, it could operate at a much slower rate than on the young Earth, possibly delaying the advent of life.
“It may be a matter of finding the sweet spot,” said co-author Robin Wordsworth of the Harvard School of Engineering and Applied Science. “There needs to be enough ultraviolet light to trigger the formation of life, but not so much that it erodes and removes the planet’s atmosphere.”
Previous studies have shown that the red dwarf stars in systems such as TRAPPIST-1 may erupt with dramatic flares in UV. If the flares deliver too much energy, they might severely damage the atmosphere and harm life on surrounding planets. On the other hand, these UV flares may provide enough energy to compensate for the lower levels of UV light steadily produced by the star.
“We still have a lot of work to do in the laboratory and elsewhere to determine how factors, including UV, play into the question of life,” said co-author Dimitar Sasselov, also of the CfA. “Also, we need to determine whether life can form at much lower UV levels than we experience here on Earth.”
There is intense interest in probing these questions because red dwarf stars provide some of the most compelling candidates for detecting putative planets with life, including those mentioned above. As telescopes such as the James Webb Space Telescope and the Giant Magellan Telescope come online in coming years, scientists need the most information possible to pick out the best targets in their search for life outside our Solar System.
One limitation of these studies is that we know only one example where life formed on a planet, the Earth, and even here we are not certain exactly how life emerged. If life is found on a red dwarf’s planet, it might imply a pathway to the origin of life that is very different from what we think might have played out on Earth.
These results were published in the July 10th, 2017 issue of The Astrophysical Journal and are available online. | 0.906548 | 3.881435 |
The serene beauty of the International Space Station gliding silently across the sky needs nothing more than the naked eye to appreciate. But when the dazzling ISS is also in conjunction with a partially eclipsed Moon, Saturn and Jupiter on the 50th anniversary of Apollo 11’s launch, be sure to look low in the southeast through south around 10:06pm BST on 16 July 2019!
Have you ever seen a dwarf planet? Of the five within our solar system recognised by the International Astronomical Union – Ceres, Pluto, Haumea, Makemake and Eris – only Ceres can be considered bright and easy to locate. It reaches opposition in the constellation of Scorpius on 29 May at magnitude +7, an easy binocular object if you follow our guide.
Observers in the UK with clear skies around 1am BST on Tuesday, 21 May can see Jupiter, the solar system’s largest planet, just 4 degrees from the waning gibbous Moon low in the south-southeast. At this time both the Moon and Jupiter fit within the same field of view of binoculars magnifying less than 10×, while telescope users can also view Jupiter’s Great Red Spot.
Skywatchers in the UK and Western Europe should look low to the south-southeast an hour before sunrise on 31 January to see a beautiful naked-eye conjunction of Venus, the old crescent Moon and Jupiter, all within a span of 8½ degrees. But if you have a telescope and live in just the right place, you can also see the Moon hide a double star.
Brilliant planet Venus attains its greatest elongation almost 47° west of the Sun at dawn in the UK on Sunday, 6 January. Find a location that offers you a view down to the southeast horizon around 7am GMT and you may catch a glimpse of Jupiter too. The planetary duo is currently 14 degrees apart, but drawing nearer for a close conjunction on 22 January.
Although Jupiter close to opposition may be stealing the other naked-eye planets’ thunder, there’s lots more to see if you’re an early riser on the weekend of 5–6 May. About an hour before sunrise finds Mars and Saturn less than the span of an outstretched hand at arm’s length apart in the UK southern sky, with the waning gibbous Moon acting as a convenient guide to each planet on successive mornings.
Set your alarm for 6am GMT if you wish to see three naked-eye planets in the UK dawn sky this week. Find a location that offers an unobstructed view of the horizon from southeast to south and let the waning Moon be your guide to locating Jupiter, Mars and Saturn on successive mornings from 7 to 11 February.
It currently pays to be an early riser if you wish to view the planets, for it’s all happening at dawn in the skies of Western Europe. Find innermost planet Mercury, see a near miss of Mars and Jupiter on 7 January, then a fabulous binocular conjunction of the waning crescent Moon, the Red planet and Jupiter on 11 January! | 0.884458 | 3.394426 |
On July 10, 2010, the European Space Agency’s Rosetta probe flew by the asteroid 21 Lutetia, which at the time was the largest asteroid ever to have been visited by a spacecraft. The fly-by occurred 282 million miles from Earth; close-up images taken by the probe revealed cracks and craters running across Lutetia’s surface, evidence of the asteroid’s long and battered history.
Now an international team of researchers from France, Germany, the Netherlands and the United States has analyzed Lutetia’s surface images, and found that underneath its cold and cracked exterior, the asteroid may in fact have once harbored a molten-hot, metallic core. The findings suggest that Lutetia, despite billions of years of impacts, may have retained its original structure — a preserved remnant of the very earliest days of the solar system.
The results are published in a series of three papers in the journals Science and Planetary Space Science (PSS).
Benjamin Weiss, an associate professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says a melted core within Lutetia may exemplify a “hidden diversity” within the greater asteroid belt.
“There might be many bodies that have cores and interesting interiors that we never noticed, because they’re covered by unmelted surfaces,” says Weiss, who is a co-author on both Science papers and lead author for the paper in PSS. “The asteroid belt may be more interesting than it seems on the surface.”
More than a rubble pile
Most asteroids careening through the asteroid belt, between the orbits of Mars and Jupiter, are scrambled versions of their former selves: essentially mashed-up masses of rock and metal that have collided and cooled over billions of years. These rocky conglomerations are relatively small and light, with voids and cracks in their interiors that make them very porous. It had been thought that the vast majority of these bodies never melted to form dense, metallic cores, but instead are just primordial piles of space rocks and dust.
In contrast, the Rosetta team — led by Holger Sierks of the Max-Planck Institute for Solar System Research and Martin Pätzold of the Rheinisches Institut für Umweltforschung, both in Germany — found that Lutetia is extremely dense. The team drew up a model of the asteroid’s shape, based on images taken by the Rosetta probe. The researchers then calculated Lutetia’s volume, mass and finally its density, which they found, in collaboration with the MIT team, to be greater than most meteorite samples measured on Earth.
The asteroid’s density would make sense if it were completely solid, free of voids or cracks. However, Rosetta researchers measured the asteroid’s surface craters and identified huge fractures throughout, suggesting the asteroid is relatively porous, a finding that didn’t quite square with the team’s density measurements — after all, the more porous an object, the less dense it should be.
Weiss and his colleagues, including MIT professor Richard Binzel and former MIT professor Linda T. Elkins-Tanton, now head of the Carnegie Institution for Science’s Department of Terrestrial Magnetism, offered a likely explanation for the discrepancy: Perhaps the space rock contains a dense metallic core, with a once melted interior underneath its fractured crust.
The direct observations from Lutetia may provide evidence for a theory developed last year by Weiss, Elkins-Tanton and MIT’s Maria Zuber. The team studied samples of chondrites, meteorites on Earth that have remained unchanged since their early formation. They found samples from the meteorite Allende that were strongly magnetized, and theorized that such magnetization most likely occurred in an asteroid with a melted, metallic core. The theory was seen as a big shift from the traditional picture of most asteroids as primordial, unmelted objects.
Planetary arrested development
If a metallic core does indeed exist, Lutetia would be the first asteroid known to be partially differentiated: having a melted interior overlain by progressively cooler layers. The asteroid would also represent a snapshot of early planetary development.
As the solar system began to take form 4.5 billion years ago, planets formed from collisions first of dust, then of larger chunks of rock. Numerous chunks remained relatively small, cooling quickly to form asteroids, while others grew with each collision, eventually reaching the size of planets. These large bodies generated an immense amount of heat — but as a new planet melted from the inside, it cooled from the outside, forming a crust around a molten core.
According to Weiss, Lutetia is a case of arrested development. The asteroid may have reached a size large enough to develop and retain a melting core, and then simply avoided the larger collisions that accelerated planet formation.
“The planets … don’t retain a record of these early differentiation processes,” Weiss says. “So this asteroid may be a relic of the first events of melting in a body.”
Erik Asphaug, a professor of planetary science at the University of California at Santa Cruz, studies “hit-and-run” collisions between early planetary bodies. He says the work by Weiss and his colleagues is a solid step toward resolving how certain asteroids like Lutetia may have evolved.
“We’ve had decades of cartoon speculation, and here’s speculation that’s anchored in physical understanding of how the interiors of these bodies would evolve,” says Asphaug, who was not involved in the research. “It’s like getting through the first 100 pages of a novel, and you don’t know where it’s leading, but it feels like the beginnings of a coherent picture.”
Weiss says while the images and measurements of Lutetia are intriguing evidence for a partially differentiated asteroid, a “smoking gun” could be provided by a sample taken directly from an asteroid. Binzel and Weiss are part of a NASA team that plans to launch a probe to an asteroid in 2016, which will take a sample and return it to Earth.
Weiss says there are a number of hurdles he and his colleagues will have to surmount before obtaining definitive evidence for a molten core.
“The challenge is, the body has to be big,” Weiss says. “If it’s not big, then it’s not going to retain a molten interior. The problem then is, all the big bodies are not going to be easily excavated. So it’s sort of a Catch-22.” | 0.811503 | 4.051821 |
Theory of relativity
See also Counterexamples to Relativity.
In physics, the theory of relativity is a scientific theory describing the effects due to the invariance of the speed of light. In particular, the meaning of space and time are altered by the motion of the observer. Relativity proposes time dilation and length contraction for observers moving relative to one another at very high ("relativistic") speeds.
Relativity refers to two closely-related mathematical theories in physics:
- Special relativity (SR) is a theory to describe the laws of motion for non-accelerating bodies traveling at a significant fraction of the speed of light. As speeds approach zero, Special Relativity tends towards equivalence with Newton's Laws of Motion. Special Relativity was put forward by Albert Einstein; its mathematical framework was independently developed and formalized by Hendrik Lorentz, Henri Poincaré, and Hermann Minkowski.
- General Relativity (GR) is a theory to explain the laws of motion as viewed from accelerating reference frames and includes a geometric explanation for gravity. This theory was originally developed by Einstein, with help from David Hilbert in its final mathematical formulation, as a generalization of the postulates of Special Relativity to account for non-inertial, accelerating observers, particularly those in a gravitational field. A dramatic but later discredited claim by Sir Arthur Eddington of experimental proof of General Relativity in 1919 popularized the theory.
These theories have augmented earlier approaches, such as Galilean Relativity.
The theory of relativity is defended with religious-like zeal, such that no college faculty tenure, Ph.D degree, or Nobel Prize is ever awarded to anyone who dares criticize the theory, as the example of denying a Nobel Prize to the most accomplished physicist of the 20th century, Robert Dicke, illustrates. Other critics of the theory are Nikola Tesla, who called it a "...magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king ... its exponents are brilliant men but they are metaphysicists, not scientists..." and Louis Essen [1908-1997], the man credited with determining the speed of light. He wrote many fiery papers against it such as Relativity and Time Signals and Relativity - Joke or Swindle?. Perhaps the most famous website opposing relativity is this one, with its Counterexamples to Relativity page. The cornerstone item in that page involves the experimental measurements of the advance of the perihelion of Mercury that show a shift greater than predicted by Relativity, well beyond the margin of error.
There are some issues of continuity and limits arising in the mathematical analysis of the theory of relativity. See Counterexamples to Relativity for discussion of this point.
The theory of relativity consist of complex mathematical equations relying on several hypotheses. For example, at Hofstra University general relativity is taught as part of an upperclass math course on differential geometry, based on three stated assumptions. Special relativity assumes that all observers in inertial frames of reference will measure the same value for the speed of light, c and that all inertial frames of reference are equivalent. These hypotheses that can never be fully tested. Relativity rejects Newton's action at a distance, which is basic to Newtonian gravity and also found to be a consequence of quantum mechanics. The mathematics of relativity assume no exceptions, yet in the time period immediately following the origin of the universe the relativity equations could not possibly have been valid, since quantum effects would not be negligible (in the same way non-relativistic quantum mechanics is not valid when dealing with particles traveling near the speed of light).
The "continuous" nature of space and time postulated by relativity is in conflict with the "discrete" nature in quantum mechanics, and although theories like string theory and quantum field theory have attempted to unify relativity and quantum mechanics, neither has been entirely successful or proven.
Unlike Newtonian physics, in which space and time intervals are each invariant as seen by all observers, in SR the only invariant quantity is a quadratic combination of space and time intervals (x2 - c2 t2). The instantaneous transmission of Newtonian gravitational effects also contradicts relativity.
In quantum mechanics, the uncertainty principle suggests that virtual particles can sometimes travel faster than the speed of light which would violate causality, but "[t]he only known way to resolve this tension involves introducing the idea of antiparticles." Consequently, in 1928 Paul Dirac derived the Dirac equation, one of the first quantum mechanical equations compatible with special relativity, by which Dirac predicted the existence of antimatter. Four years later, antimatter (the positron) was discovered by Carl Anderson, as successfully predicted by relativistic quantum mechanics. Quantum field theory, a generalization of quantum mechanics, is fully compatible with special relativity but not with general relativity, and still lacks a vital piece: evidence of the graviton.
- 1 Special Relativity
- 2 General Relativity
- 3 Lack of evidence for Relativity
- 4 Experimental and Observational Evidence Confirming Relativity
- 4.1 The Michelson-Morley experiment
- 4.2 Mass Change Associated With Energy Change
- 4.3 Time Dilation
- 4.4 The Cockcroft and Walton Experiment
- 4.5 Bending of Light in a Gravitational Field
- 4.6 Precession of the orbit of Mercury
- 4.7 The Shapiro Effect
- 4.8 Gravitational Time Dilation
- 4.9 Gravitational Waves
- 4.10 Local Position Invariance
- 4.11 Further Measurements near Sagittarius A*
- 4.12 Geodetic Precession
- 5 Predicted consequences of the Theories
- 6 Relativity in everyday life
- 7 Paradoxes
- 8 Speed "paradox"
- 9 Variable Speed of Light
- 10 Pending research
- 11 Political aspects of relativity
- 12 See also
- 13 References
- 14 External links
Lorentz and Poincaré developed Special Relativity as way of understanding how Maxwell's equations for electromagnetism could be valid in different frames of reference. Einstein famously published an explanation of Poincaré's theory in terms of two assumptions (postulates):
- The laws of physics are identical in all inertial reference frames.
- The speed of light is the same for all (inertial) observers, regardless of their velocities relative to each other.
As an example of the first of these, if one performs an experiment—say, with a pendulum or some similar apparatus—in a railroad car traveling uniformly at 50 miles per hour, one would find the results of the experiment (positions, speeds, etc.) to be consistent with the laws of physics in the railroad car. An outside stationary observer, looking through the window, would also find the results consistent with the laws of physics in his stationary reference frame. He would simply have to subtract 50 miles per hour from the velocities of the objects in order to get values that agree with the values obtained by the observer on the train. But the two observations would each be consistent with the laws of physics. This is all straightforward and obvious to modern people, and has been since the time of Galileo. This principle is now called "Galilean relativity". Another way of stating this is:
- There is no "preferred" frame of reference.
Neither observer can claim that his frame of reference is "right". Of course, the observer on the train would think that the Earth is moving at 50 miles per hour under the wheels.
The second postulate is what makes relativity what it is. Using the above principle, if someone in the railroad car shines a beam of light forward, he would observe it moving at a speed of 670,000,000 miles per hour. One would expect, according to the first postulate, that an observer standing on the ground would measure its speed as 670,000,050 miles per hour. But the second postulate says that the stationary observer measures the same speed, 670,000,000 miles per hour. While this seems paradoxical, many experiments, such as the Michelson-Morley experiment show that it is nevertheless true. Special Relativity explains the apparent inconsistency between these postulates.
Why was this not observed until around 1900? Because the speed of light is so great that the discrepancy is very hard to measure. For example, in the railroad experiment described above, the discrepancy between the two speeds is 7.5 parts per million.
There are many far-reaching consequences of this, and many experimental verifications, some of which are listed below. Two of the more interesting consequences are that:
- No material object of nonzero mass can travel at or greater than the speed of light. (Objects of zero mass, such as photons, travel at exactly the speed of light.)
- Information can not travel faster than the speed of light. This is sometimes stated as:
- There is no "action at a distance," because that would make observations dependent on the frame of reference. See Action at a distance for a discussion of this point.
When the assumptions are stated clearly as above, the weaknesses in the theory are more apparent. There “is” action at a distance in quantum entanglement and apparently also in gravity, as no gravitons can be found. However, no information has yet been transmitted via quantum entanglement, so while non-locality violates the spirit of relativity it is consistent with it if relativity is limited to the transmission of information. Quantum field theory, an attempt to partially reconcile quantum mechanics with relativity, is incomplete at best. As to the second assumption, it is contrary to the arrow of time, which illustrates the lack of symmetry in time. Logical defects include the incoherence of relativistic mass (see discussion below) and the lack of relativistic constraints near the beginning the universe (see above).
Special Relativity (SR) was initially developed by Henri Poincaré and Hendrik Lorentz, working on problems in electrodynamics and the Michelson-Morley experiment, which had not found any sign of Earth's orbital motion through the luminiferous aether, which was believed to be the substance which carried electromagnetic waves. Special relativity alters Isaac Newton's laws of motion by assuming that the speed of light will be the same for all observers, despite their relative velocities and the source of the light. (Therefore, if A sends a beam of light to B, and both measure the speed, it will be the same for both, no matter what the relative velocity of A and B. In Newtonian/Galilean mechanics, If A sends a physical object at a particular velocity towards B, and nothing slows it, the velocity of the object relative to B depends on the velocities of the object and of B relative to A.)
At low speeds (relative to light-speed), the Lorentz-Poincaré relativity equations are equivalent to Newton's equations. The media-promoted equation E=mc², implausibly suggests a relationship between typically unrelated concepts of energy, the rest mass of a body and the speed of light.
Under relativity, particles at low mass and low speed can be accurately approximated by classical mechanics (such as Isaac Newton's laws of motion). At the two extremes, modeling the behavior of electrons requires that relativistic effects be taken into account (the chemically significant phenomenon of electron spin arises from relativity), and the course of light passing through a region containing many massive bodies such as galaxies will be distorted (classical mechanics, in which light travels in straight lines, does not predict this). These are both experimentally confirmed (electron spin was known before relativity arose, and telescopic observations confirm that galactic clusters distort the paths of the light passing through them).
Many scientists have indicated problems with the postulates of special relativity. Paul Davies, formerly of Macquarie University and now at the University of Arizona believes that the speed of light has changed over time. Since the speed of light is a constant speed 'c' this indicates problems with the theory light speed. Other engineers and scientists have written about problems in the basic set of special relativity equations. Based on the ideas of not Einstein but of the scientist Fitzgerald as well as others, a length contraction effect was predicted as an explanation of the failure of the Michelson-Morley experiment to detect Earth's orbital motion. This idea was taken up by Hendrik Lorentz and shown by others to be a useful mechanism by which theory could be derived from experimental results. In fact, the Michelson-Morley experiment is often cited in textbooks as the derivation of relativity, though there are many other experiments that do this; see below.
In 2005, Michael Strauss, a computer engineer, claimed to have shown clear contradictions in Special Relativity, invalidating much of it. In 2004 he wrote the book Requiem for Relativity (The Collapse of Special Relativity), ASIN 0976312506. An archived ad for the book may be found at . The original web site for it is no longer active.
- See the General theory of relativity page for more in-depth coverage of this topic.
General Relativity is a theory of gravity that is compatible with Special Relativity. Einstein explains a thought experiment involving two elevators. The first elevator is stationary on the Earth, while the other is being pulled through space at a constant acceleration of g. Einstein realized that any physical experiment carried out in the elevators would give the same result. This realization is known as the equivalence principle and it states that accelerating frames of reference and gravitational fields are indistinguishable. General Relativity is the theory of gravity that incorporates Special Relativity and the equivalence principle.
General Relativity is a mathematical extension of Special Relativity. GR views space-time as a 4-dimensional manifold, which looks locally like Minkowski space, and which acquires curvature due to the presence of massive bodies. Thus, near massive bodies, the geometry of space-time differs to a large degree from that of other parts of the universe. Just as in classical physics, objects travel along geodesics in the absence of external forces. Importantly though, near a massive body, geodesics are no longer straight lines. It is this phenomenon of objects traveling along geodesics in a curved spacetime that accounts for gravity.
The "anomalous precession" of Mercury's perihelion (slow shift of the orbit's major axis) is explained by the Theory of General Relativity, but not by Newtonian mechanics. Some precession (5600 arcseconds per century) is caused by purely classical phenomena, mostly the gravitational attraction of other planets. But a small amount (43 arcseconds per century) of the observed precession, goes beyond that which classical Newtonian mechanics can explain. General relativity explains it accurately. There was another explanation based on Newtonian gravity, involving a slight alteration to the precise inverse-square relation of Newtonian gravity to distance, but it was quickly discarded when it gave very bad results for the Moon's orbit. The relativistic explanation of the anomalous precession is disputed on the Counterexamples to Relativity page of Conservapedia.
British Historian Paul Johnson declared the turning point in 20th century to have been when fellow Briton Sir Arthur Eddington, an esteemed English astronomer, ventured out on a boat off Africa in 1919 with a local Army unit to observe the bending of starlight around the sun during a total eclipse. Upon his return to England declared that his observations proven the theory of relativity. In fact recent analysis of Eddington's work revealed that he was biased in selecting his data, and that overall his data were inconclusive about the theory of relativity. The prediction was later confirmed by more rigorous experiments, such as those performed by the Hubble Space Telescope. Hendrik Lorentz had this to say on the discrepancies between the empirical eclipse data and Einstein's predictions.
- It indeed seems that the discrepancies may be ascribed to faults in observations, which supposition is supported by the fact that the observations at Prince's Island, which, it is true, did not turn out quite as well as those mentioned above, gave the result, of 1.64, somewhat lower than Einstein's figure.
The bending of light by gravity is predicted both by Newtonian physics and relativity. Experimental observation agrees with the latter amount (1.75 arcseconds for the Sun), rather approximately for Eddington's measurements, and very accurately for more modern measurements.
Special relativity is the limiting case of general relativity where all gravitational fields are weak. Alternatively, special relativity is the limiting case of general relativity when all reference frames are inertial (non-accelerating and without gravity).
Lack of evidence for Relativity
The Theory of relativity assumes that time is symmetric just as space is, but the biggest early promoter of relativity, Arthur Eddington, coined the term "arrow of time" admitting how time is not symmetric but is directional. The passage of time is tied to an increase in disorder, or entropy. The Theory of relativity cannot explain this, and implicitly denies it, specifically allowing for theoretical time travel (e.g., wormholes) and different rates of passage of time based on velocity and acceleration.
The Global Positioning System (GPS) requires exquisitely accurate timekeeping in the satellite clocks—down to the nanosecond. This precision is so great that the effects of both special relativity and general relativity play an important role. Without making corrections to the timing signals from the satellite clocks, the results of GPS measurements would be so far off that the system would be useless. The required amount of correction is well known, and the system makes those corrections. Those corrections are consistent with special relativity and general relativity, and it is generally accepted that this is no coincidence—relativistic effects are the reason why the corrections are necessary. But one doesn't need to believe that relativity is the reason the corrections are needed; one only needs to make the corrections in order to get the system to work.
Tom Van Flandern, an astronomer hired to work on GPS in the late 1990s, concluded that "[t]he GPS programmers don't need relativity." He was quoted as saying that the GPS programmers "have basically blown off Einstein." Asynchronization can be easily addressed through communications between the satellites and ground stations, so it is unclear why any theory would be needed for GPS. While Van Flandern believed that relativity is unnecessary for GPS, he also asserted that observations of GPS satellites supported both general and special relativity, writing that "we can assert with confidence that the predictions of relativity are confirmed to high accuracy over time periods of many days," with unrelated factors interfering with longer-term observations.
Some internet articles claim that GPS timing differences confirm the Theory of Relativity or its Lorentzian counterpart (which uses a preferred frame of reference). GPS clocks run slower in the weaker gravitation field of the satellites than on ground stations on Earth, with the effects predicted by general relativity far outweighing the effects predicted by special relativity. However, the articles claiming that the slower GPS satellite clocks confirm relativity do not address the effect, if any, of the weaker gravitational force under Newton's theory on the GPS satellite clocks, likely because in Newtonian Mechanics every clock in the universe keeps time at the same rate regardless of velocity, acceleration, or the presence or absence of force.
Currently, GPS satellites are synchronized to Coordinated Universal Time by radio signals from the ground; therefore, they cannot currently be used to test general relativity.
There are claims that the effects of relativity have been observed with the frequency shift of the signal being sent back to Earth several times as various spacecraft have dipped into the gravity wells around massive objects such as the sun (see image at right) or Saturn. A satellite called Gravity Probe B was put in orbit about the Earth to examine the effects of frame dragging and geodetic warping of space, but the results were inconclusive. Note, however, that Newtonian mechanics also predicts deflection of light by gravity, and in the initial theory of relativity it predicted the same amount of deflection, but only if we treat light as capable of being accelerated and decelerated like ordinary matter, which is contrary to all measurements and observations to date. Adjustments to the theory of relativity resulted in a prediction of a greater deflection of light than that predicated by Newtonian mechanics, though it is debatable how much deflection Newtonian mechanics should predict.
None of the NASA spacecraft incorporates predictions of relativity into their own timing mechanisms, as Newtonian mechanics is adequate even for probes sent deep into space so long as they do not undergo accelerations near the speed of light or enter any massive gravity wells.
A decade of observation of the pulsar pair PSR B1913+16 detected a decline in its orbital period, which was attributed to a loss in energy by the system. It is impossible to measure the masses of the pulsars, their accelerations relative to the observers, or other fundamental parameters. Professors Joseph Taylor and Russell Hulse, who discovered the binary pulsar, found that physical values could be assigned to the pulsars to make the observed decline in orbital period consistent with the Theory of General Relativity, and for this they were awarded the 1993 Nobel Prize for Physics, which is the only award ever given by the Nobel committee for the Theory of Relativity. In 2004, Professor Taylor utilized a correction to the derivative of the orbital period to fit subsequent data better to the theory. At most, assumptions can be made and altered to fit the data to the theory, rather than the data confirming the theory.
The perihelion of Mercury's orbit precesses at a measurable rate, but even after accounting for gravitational perturbations caused all other planets in the solar system, Newton's theory (assuming a precise inverse-square relationship for distance) predicts a rate of precession that differs from the measured rate by approximately 43 arcseconds per century. While general relativity was developed on purely theoretical grounds, it was soon discovered that it explained these precession observations. Newton's theory can also explain the Mercury precession by making tiny adjustments to parameters in the gravitational equation, but doing so would give the same precession for all orbiting bodies everywhere, a phenomenon which is not observed.
General relativity predicts twice as much bending in light as it passes near massive objects than Newton's theory might predict. This phenomenon is known as gravitational lensing. A large number of instances of gravitational lensing have been observed, and it is now a standard astronomical tool. Note, however, that the extent of bending of light predicted by Newton's theory is open to debate, and depends on assumptions about the nature of light for gravitational purposes.
In 1972, scientists flew extremely accurate clocks ("atomic clocks") around the world in both directions on commercial airlines, and claimed to observe relativistic time dilation; the eastbound clock gained 273 ns and the westbound clock lost 59 ns, matching the predictions of general relativity to within experimental accuracy. However, the inventor of the atomic clock, Louis Essen, declared that the experiment was inaccurate. Dr A. G. Kelly examined the raw data from the experiment and declared it inconclusive. The Nobel Committee chose not to honor this experiment for the significance that was claimed.
Experimental and Observational Evidence Confirming Relativity
The different effects predicted by special relativity, compared to classical formulations, are extremely tiny. Most relativistic effects are negligible at the speeds of ordinary phenomena observed by humans. The effects only become significant when the speeds involved are a significant fraction of the speed of light, which is meters per second—such speeds are called relativistic. (However, it's worth noting that ordinary magnetism can be considered an effect of relativity, dictated by the need for electrostatic theory to be correct under relativity. The speed of light in fact appears in the formulas (Maxwell's Equations) governing electricity and magnetism, though these equations were developed long before relativity was proposed.)
Because the effects of relativity are so tiny, scientists have been devising sophisticated and sensitive tests ever since the theory was formulated in 1905.
It is important to be aware that it is fairly rare for an experiment to prove a theory. In general, experiments can only refute a theory. They can also be consistent with a theory. When enough experiments, especially experiments that investigate a wide variety of phenomena, are shown to be consistent with a theory, it lends credence to that theory. When no other plausible theory can explain those observations, we can say that they validate the theory. The Mercury observations are just one phenomenon. By themselves they couldn't validate or prove GR. And there was at one time another competing theory—the Newcomb-Hall exponent-fudging theory. That one didn't hold up for things other than Mercury. No other theory has come up explaining the phenomenon; SR and GR have withstood the test of time. That goes a long way toward validating them. There are many other observations and experiments, covering a wide variety of phenomena, described below—bending of light, gravitational time dilation, gravitational waves, geodetic precession, Shapiro effect, etc. It is these widely disparate observations, and the lack of any alternative theories explaining any of them, that lead people to say that SR and GR are "experimentally validated".
There's also the matter of simply "accepting" something, when a phenomenon is consistent with a theory that is already known to be valid. The recoil from a gun is an example of this. Everyone knows that there is a backward recoil when a gun is fired. This is explained to people when they are first being taught how to use a gun, and they get used to it with practice. The reason for the recoil is that it is an obvious consequence of Newtons' laws of motion. But people don't specifically think about Newton's laws, or consider this to be a "proof", when they are firing a gun. They just accept that the recoil is a known consequence of those laws. Newton's laws of motion have been validated through thousands of experiments much more focused than the firing of a gun.
The Cockcroft/Walton experiment is an example of this kind of acceptance. The results are consistent (to within 5% when analyzed carefully) with Special Relativity, and many people consider it to be a validation of SR. But there were too many other things going on, such as the use of the newly-invented particle accelerator, to make it a definitive test. One would have to think very carefully about what assumptions have to be made about what is happening in the experiment if one wanted to use it to assert anything about E=mc². However, famous as the experiment was at the time, it is no longer suggested as a validation of this formula. Special Relativity had already been validated through more focused and definitive tests. There are no known alternative theories, published in the scientific literature or listed in Counterexamples to Relativity, explaining the loss of mass. See Cockcroft and Walton Experiment.
The anomalous behavior of the timing signals from GPS satellites is another example. The phenomenon is well known—the system compensates for this; otherwise it wouldn't work—and the phenomenon is known to be a consequence of both special and general relativity. But the GPS system should not be considered and experiment to test relativity. No sensible person would build the GPS system as a test of relativity, if only because it exhibits two phenomena (time dilation of special relativity, 7 milliseconds per day, and time compression of general relativity, 45 milliseconds per day) that work against each other. No one would design an experiment that tests two phenomena working against each other.
The bending of light in a gravitational field is another example. (In fact, it was the first, and, for a while, most famous piece of evidence in favor of GR, even though it was sloppily done.) Newtonian physics also might predict the bending of light depending on whether one posits the "wave" formulation (deflection is zero) or the "particle" formulation (deflection is 0.875 arc seconds). But the actual deflection is 1.75 arc seconds, and GR predicts this value. The are no known versions of Newtonian gravity that get this larger value.
While the experimental tests for General Relativity are rather esoteric, those for Special Relativity are fairly straightforward. So much so that the Michelson-Morley experiment could be said to have single-handedly established the case for SR—the logical syllogism leading from Michelson-Morley to SR and the Lorentz transform was fairly clear once people saw it.
When analyzing an experiment to see whether it validates a theory, one must be careful not to assume the theory in one's reasoning. For establishing Special Relativity with the Michelson-Morley experiment, the assumptions are:
- Newtonian and Galilean mechanics.
- Galilean relativity, that is, the notion that there is no absolute frame of reference.
- The universality of the speed of light.
- And, of course, proper calibration of the equipment.
- The third one was the observation that Michelson and Morley made.
- For the derivation of E=mc², these assumptions are added:
- Conservation of energy.
- Conservation of momentum.
- All of the assumptions listed above constitute SR.
- It would be nearly inconceivable to derive GR without SR. Gravitational time dilation, for example, requires a lot of information coming from SR.
- So, for the experiments listed below for GR, the assumptions are the 6 above plus:
- The Equivalence Principle.
- So the experiments below for GR are really just establishing that the Equivalence Principle is valid, and that GR follows logically from that.
The most famous experiment, and the one that is commonly cited in textbooks as the experiment that established the case for relativity, was the Michelson-Morley experiment. This showed that all observers will obtain the same measured value for the speed of light (3x108 meters per second) no matter what their state of motion. This is the first of the two fundamental principles:
- The speed of light is constant for all observers, regardless of their velocities relative to each other.
- The laws of physics are identical in all reference frames.
(The second is just a restatement of Galilean relativity, that is, the "common sense" that had been accepted for centuries.) A naive "common sense" interpretation of Galilean relativity would require that measurements of the speed of light (or anything else) by different observers would get results that differ by the observers' relative speeds, and hence that principle #1 can't be true. Special relativity fixes this apparent paradox.
All of special relativity derives for these two principles, plus assumptions of exact conservation of momentum and energy in all cases.
There are hundreds of experiments or observations that, to varying extents, "prove", "validate", or "are consistent with" special and general relativity. A good survey may be found at this site. Some experiments can be as simple as a spinning Alnico magnet and a voltmeter, that can be performed on a tabletop in a science classroom. Just a few of the more important ones will be described here.
This is the most famous experiment, and is often taken as the experiment establishing the correctness of special relativity. It is described elsewhere.
Mass Change Associated With Energy Change
This is the famous formula "E=mc²". At the end of Einstein's original 1905 paper on the subject, he speculates on the possibility that the equation , which would normally be very hard to verify, could be verified with the extremely high energies of the newly discovered phenomenon of radioactivity. In the 1910s, with the invention of the mass spectrometer, it became possible to measure masses of nuclei accurately. This led to the clearing up of the mystery of atomic masses not being exact integers,and strongly suggested the existence of a "mass defect" (or "packing fraction") consistent with the mass-energy equivalence. In the 1930s, experiments with known nuclear reactions showed a very accurate correlation between the masses of the nuclei involved and the energy released. See Quantitative Analysis of Alpha Decay.
Another prediction of special relativity was time dilation in rapidly moving objects. This effect was most famously verified in the anomalously slow decay of relativistic cosmic muons. Time dilation has since been verified many times, and is routinely taken into account in all high-energy nuclear physics experiments, as in Hadron collision experiments.
This one is quite famous, because it was one of the earliest observations of phenomena involving mass change. But, as noted above, it can't really be taken as a "proof" of relativity.
Bending of Light in a Gravitational Field
Unlike special relativity, predictions of general relativity turn out to be obscure and difficult to test. The two most famous predictions in the early days were the bending of light in a gravitational field and the precession of the perihelia of orbiting planets. Several other phenomena have arisen more recently.
The first of these was famously tested during a total eclipse in 1919. That test was somewhat muddled by an incorrect initial calculation, by several people including Einstein himself, of what the effect would be, and some "cherry picking" of the data to be used. The observed result was about 1.5 arc seconds. The data selection could be considered "manipulation" or "fudging", by a person (Arthur Eddington) who had a personal stake in the outcome. His analysis techniques would not pass muster today. The announcement of this test, flawed though it was, made Einstein world-famous.
It should be noted that pre-relativistic (Newtonian) physics may also predict a bending, depending on whether one uses the 17th century "corpuscular" formulation or the 19th century "wave" formulation. The former would give a value of 0.875 arc seconds, while the latter would give a value of zero.
Relying on the usual assumptions—Newtonian mechanics, Galilean relativity, conservation of energy and momentum, the universality of the speed of light (that is, special relativity), the Equivalence Principle, and the geodesic equation in empty space (that is, general relativity), and the proper calibration of the instruments, observations of later eclipses, and the observations of quasar 3C273, confirm predictions of the theory, which is that the bending is 1.75 arc seconds.
Precession of the orbit of Mercury
The second "classical" test of general relativity was the advance of the perihelion of the orbit of Mercury. There are many complex effects contributing to this, including gravitational perturbations from other planets and the effect of the oblateness of the Sun. These are hard to calculate accurately, but, by 1860 it was known quite accurately that there was an "anomalous" precession, that is, a precession beyond all other known effects, of 43 arc seconds per century. This is a very tiny effect, but astronomical measurements were sufficiently accurate by that time to show it clearly. This was based on observations going all the way back to about 1700. It was calculated with great accuracy, and reported in 1859, by Urbain Leverrier. This was long before relativity was formulated.
- One might wonder how astronomical observations accurate enough to measure such a tiny effect could have been made with the technology of that era. A clever trick was used: Solar transits of Mercury were observed and timed. Some of these transits were timed with an accuracy of about 15 seconds.
- This created quite a problem—physicists by then were accustomed to having their theories check out very accurately. One proposal that was made, by Simon Newcomb and Asaph Hall, was that the exponent of the radius in the gravitational formula wasn't exactly 2. He showed that, by choosing an exponent of , the precession, as a fraction of a full orbit per planet's year, is . By setting to .000000157, that is, an exponent of 2.000000157, Newcomb was able to get a precession of .000000078 revolutions per Mercury year, or 43 arcseconds per Earth year. Whatever value is chosen for , it gives the same precession, per revolution, for all orbiting bodies, but gravitational effects from other planets diminish that effect the further the planet is from the sun.
- The approximation given at the end of Einstein's 1916 paper is revolutions per planet's "year", where a is the semi-major axis, T is the length of the planet's year, and e is the eccentricity. A much simpler, but less accurate, approximation, designed to show how the precession relates to the planet's speed, is revolutions per planet's "year", where is the planet's average orbital speed. These are just approximations. Getting an accurate value requires integrating the geodesic equation of the Schwartzschild metric, where Ricci's tensor is zero.
- While Newcomb's theory, and general relativity, don't lead to closed-form solutions, both theories can be solved numerically to as much precision as one desires.
- The following table shows some approximate parameters for the planets. Note that Mercury has the smallest orbit, and the fastest speed. Precession of planets other than Mercury is extremely hard to measure, but measurements of the actual anomalous precessions are in good agreement.
|Planet||Period, seconds x 106||Semimajor axis, meters x 109||Speed, meters/second x 103||Gravitational force, Newtons per kilogram||Anomalous precession, arcseconds per (Earth) century, pure Newtonian mechanics||Anomalous precession, Newtonian with exponent of 2.000000157||Anomalous precession, general relativity||Measured anomalous precession (estimated uncertainty)|
- Considering only the anomalous precession, that is, the precession that remains after all known other factors (other planets and asteroids, solar oblateness) have been accounted for, and using very accurate calculations rather than the approximations given above, general relativity predicts 42.98 ±0.04 arcseconds per century. Some observed values, as of 2008, are:
- 43.11 ± 0.21 (Shapiro et al., 1976)
- 42.92 ± 0.20 (Anderson et al., 1987)
- 42.94 ± 0.20 (Anderson et al., 1991)
- 43.13 ± 0.14 (Anderson et al., 1992)
- (Source: Pijpers 2008)
- These error bars, and that of the general relativity prediction, all overlap.
- No Nobel Prize was was awarded for this.
The Shapiro Effect
Another is the Shapiro effect, involving time delay in radio signals passing through the gravity well of the Sun or a planet. Various spacecraft (such as Cassini) have confirmed this.
Gravitational Time Dilation
Gravitational time dilation is an effect separate from the time dilation of special relativity. It was tested by the Pound-Rebka experiment in 1959. No Nobel Prize was awarded for this. Professor Pound had previously shared in the 1952 Nobel for his contributions to Nuclear Magnetic Resonance imaging.
Later in the 20th century, even more subtle phenomena were tested. One was the phenomenon of gravitational radiation, or "gravitational waves". These waves are incredibly difficult to observe, and had never been observed until 2015. But extremely dense binary pulsars radiate gravitational waves with sufficient energy loss that, even though we can't detect the waves from Earth, we can see the effect of the energy loss from the radiation. The extreme precision of the timing of pulses from pulsars makes it possible to observe their energy loss with great accuracy. Observations by Hulse and Taylor of the pulsar pair known as B1913+16, found the energy loss to be consistent with the predicted radiation. This required choosing orbital parameters to be consistent with observation, in the same way that Kepler chose orbital parameters to fit observed planetary motion to his theory. The rotating pulsars have since moved such that Earth is now out of the beams. The assumptions required for this, in addition to those listed above, were that pulsars behave consistently. The 1993 Nobel Prize in physics was awarded for this.
In late 2015 (and announced in 2016), the LIGO instruments directly detected gravitational waves allegedly from colliding black holes. See Gravitational waves. Unlike the waves from orbiting pulsars, that could only be detected by the loss of rotation energy, the waves from colliding black holes were strong enough to be detected directly. The assumptions required for this, in addition to those listed above, were that the objects emitting the radiation (generally believed to be black holes, of course) satisfy the Schwartzschild solution to relativistic mechanics. The 2017 Nobel Prize in physics was awarded for this.
Since that very early announcement, further observations of gravitational waves have continued to come in. In August 2019 the first detection of the gravitational waves from the merger of a black hole and a neutron star occurred. This was event S190814bv, 870 million light years away, and hence actually occurred 870 million years ago.
In 2018 an observation of the 3-body system PSR J0337+1715, consisting of 2 white dwarfs and a pulsar, was consistent with (and hence tended to confirm) general relativity under conditions of extremely high gravity, to enormous precision. The assumptions made were the same as those listed above. One of the researchers stated "If there is a difference [between observation and the prediction of the Equivalence Principle], it is no more than three parts in a million."
In 2018, observations of a star orbiting the supermassive black hole "Sagittarius A*" at the center of our galaxy, showed that the light was stretched from the black hole's gravity just as relativity predicted. The star orbits Sagittarius A* at speeds of up to 16 million miles per hour. This was the first observation of such intense gravity.
Local Position Invariance
The equivalence principle, which is the underpinning of gravity under general relativity, states that there is absolutely no perceived effect of gravity on an object in free fall, that is, in a gravitational field. This has been tested many times, and is the basis of all space-time calculations in relativity. But in March 2019, it was reported to have been successfully tested in a gravitational field very much stronger than ever before. The phenomenon is called local position invariance, or LPI. It was measured on the light emitted from a star called "S0-2", closely orbiting the "Sagittarius A*" black hole at the center of the galaxy. The gravitational field that S0-2 is subject to is vastly more powerful than any other gravitational field that has been measured.
Further Measurements near Sagittarius A*
In July 2019, another star, S0-102, was characterized accurately by Andrea Ghez and her team. It is even closer to the Sagittarius A* black hole than S0-2. Together, the two stars made it possible to map the gravity well in 3 dimensions, providing an even more accurate test of General Relativity. "Making a measurement of such fundamental importance has required years of patient observing, enabled by state-of-the-art technology. Through their rigorous efforts, Ghez and her collaborators have produced a high-significance validation of Einstein's idea about strong gravity." The statistical significance of these measurements is 5-sigma (5σ). That means that the probability that this result came about by sheer chance is 1 in 3.5 million. It is the commonly accepted criterion for definitive validations.
Geodetic precession (also known as "de Sitter precession"), and frame dragging (also known as the "Lense-Thirring effect") were tested by the "Gravity Probe B" satellite early in the 21st century. The precision required to observe this was phenomenal. The results were announced on May 4, 2011.
Predicted consequences of the Theories
One important consequence of relativity is that an observer in one reference frame will not in general observe a clock in another frame to be "ticking" at the same rate as one in the observer's own frame.
In special relativity, where acceleration and gravitational effects are ignored, this can be derived using basic geometry. The result is that clocks in all other inertial frames of reference other than the one you are in appear to tick slower. This can be summarised by the well known phrase "moving clocks run slow".
However, with general relativity, there are similar effects such as gravitational time dilation where a clockthat is higher in a gravitational field runs faster. Often the effects of relativity are negligible. However the high precision required for the GPS system needs relativistic corrections. The rest of this section will concern only special relativity.
The length of an event , as seen by a (relative) stationary observer observing an event is given by:
- is the "proper time" or the length of the event in the observed frame of reference.
- is the relative velocity between the reference frames.
- is the speed of light (3x108 m s-1).
Evidence for time dilation was discovered by studying muon decay. Muons are subatomic particles with a short halflife of 1.53 microseconds. When produced by interactions of cosmic rays in the upper atmosphere, they have a speed around 0.994c. By putting muon detectors at the top (D1) and bottom (D2) of a mountain with a separation of 1900 m, scientists could measure accurately the proportion of muons reaching the second detector in comparison to the first. The proportion found was different to the proportion that was calculated without taking into account relativistic effects.
Using the equation for exponential decay, they could use this proportion to calculate the time taken for the muons to decay, relative to the muon. Then, using the time dilation equation they could then work out the dilated time. The dilated time showed a good correlation with the time it took the muons to reach the second sensor, thereby supporting the existence of time dilation.
The time taken for a muon to travel from D1 to D2 as measured by a stationary observer is:
The fraction of muons arriving at D2 in comparison to D1 was 0.732. (Given by )
Since (from the equation for exponential decay) then
This gives the time for the proportion of decay to occur for an observer who is stationary, relative to the muon.
Putting this into the time dilation equation gives:
This is in good agreement with the value calculated above, thereby providing evidence to support time dilation.
Since either reference frame is equally valid, from the muon's point of view it sees the earth approach it at nearly the speed of light. Hence time passes faster for the muon (slower for an observer on the ground). This appears to be a contradiction. However, the muon sees the height of the mountain contracted and so travels a shorter distance in its own frame. See length contraction below.
Time Dilation and Creation Science
For a more detailed treatment, see Starlight problem#Humphreys.27_model.
Creation scientists such as physicists Dr. Russell Humphreys and Dr. John Hartnett have used relativistic time dilation to explain how the earth can be only 6,000 years old even though cosmological data (background radiation, supernovae, etc.) set a much older age for the universe.
Derivation of Time Dilation
Time dilation is most easily derived using the Lorentz transformations, though geometrical solution is also straight forward. Using the transformation relating time between two frames of reference, and . We can find the time difference between two events that occur at the same location in space. The events shall be called event one and event 2. This results in the equations:
Subtracting the top equation from the bottom produces the time between the events as measured in each reference frame, so:
This the equation for time dilation and is the same equation as earlier.
When two inertial reference frames move past each other in a straight line with constant relative velocity, an observer in one reference frame would observe a metre rule in the other frame to be shorter along the direction parallel to the relative motion.
The length, , of an object as seen by a (relative) stationary observer is given by:
- is the "proper length" or the length of the object in its own frame of reference.
- is the relative velocity between the reference frames.
- is the speed of light m s-1
- is the Lorentz factor
Length contraction may be derived using the Lorentz transformations as with time dilation. This time we use the equation for . In this case, the time in the undashed frame must be the same. Following the same procedure as above we find that:
This is the same as above with and being the lengths in the undashed and dashed frames respectively. Again, geometrical arguments may be used to achieve the same result.
Apparent mass increase
Under this view, the mass, , of an object as detected by a (relative) stationary observer is given by:
- is the "rest mass" or the mass of the object measured by an observer in the same reference frame as the object.
- is the relative velocity of the object.
- is the speed of light (3x108 ms-1).
Since speed is relative, it follows that two observers in different inertial reference frames may disagree on the mass and kinetic energy of a body. Since all inertial reference frames are treated on an equal footing, it follows that mass and energy are interchangeable.
In recent years most physicists have shifted away from Einstein's original reliance on relativistic mass and his suggestion that mass increases[Citation Needed]. Instead, most physicists today teach that
- is the momentum defined by
- is the standard Lorentz factor
- is the proper time
Force F defined this way is a vector and thus can handle the directional aspect of the relativistic effects better than the concept of relativistic mass can. The abandonment by physicists of the concept of relativistic mass, however, has the consequence of undermining the traditional claim under relativity that
also popularly known as
Now a concept of the 4-momentum of a particle is taught, such that the square of the magnitude of satisfies:
in any inertial reference frame. The magnitude of the 4-momentum, in any inertial frame, equals the rest mass of the particle (in units where ).
Relativity in everyday life
Due to the small speeds and gravitational fields in normal life, relativistic phenomena such as time dilation and length contraction are rarely observed. However some things in everyday life can be explained using relativity:
- GPS, the satellites experience time dilation due to the difference in speed and the strength of gravitational field between the satellite and the ground. This is corrected by daily synchronisation between the ground and the atomic clocks in the satellites.
- While most elemental metals such as silver, zinc and mercury have a silver/grey appearance, some metals like gold and copper do not. This difference can be explained using relativistic quantum mechanics.
The predictions of the theory of relativity throw up a number of apparent paradoxes and anomalies relating to the effects of time dilatation and length contraction. Whilst these paradoxes are consistent with the theory, they are contrary to everyday human experience and therefore can seem like impossibilities.
The Twin Paradox
The twin paradox is usually stated as a thought experiment involving two twins, one of whom is sent on a long journey in a spacecraft travelling at close to the speed of light, whilst the other remains on Earth. Time dilatation means that the travelling twin, on his return to Earth, is younger that the twin who has remained at home. However, because neither twin is in a special position - each being in an inertial frame of reference - the reverse must also be true, and so the twin remaining on Earth must be younger. Hence each twin is younger than the other - a paradox.
The problem can be resolved in two ways. One is to examine the effects of General Relativity: to come back to Earth, the travelling twin must undergo acceleration in order to reverse his course, causing temporal effects which make him permanently the younger. Alternatively, it can be explained entirely using Special Relativity and noting that the twins are not in symmetrical situations: the one on earth has remained in a single inertial frame of reference, whilst the travelling twin has travelled in two. Note that the length of the trip cannot be increased as to make the acceleration negligible.
The Ehrenfest Paradox
The Ehrenfest Paradox considers a rigid wheel or disc rotating a bout its axis at high speed (somewhat like a bicycle wheel spinning freely on its axle). The rim of the wheel travels at close to the speed of light and therefore undergoes length contraction, whereas the radius (the spokes, for the bicycle wheel) does not. Hence the circumference is no longer equal to 2r, which is paradoxical.
The apparent paradox was finally resolved in 1975 by the Norwegian scientist Øyvind Grøn.
This is not a paradox. It arises from failure to know or understand the "speed addition" formula. The formula tells how fast each observer measures the speed of the other observer when they are both traveling toward each other, as seen by some outside observer, at speeds and . Under classical mechanics, the result is just . But the formula under special relativity is
This formula is a consequence of the Lorentz transform. It is a well known part of the basic undergraduate physics curriculum.
So, if two spacecraft are approaching each other, each traveling at what an outside observer would measure as half the speed of light, a person ignorant of how relativity works might think they each see the other coming toward them at the speed of light. But the formula shows that they actually see each other moving at of the speed of light.
If and are both less than the speed of light, one can show that the result of the addition formula will be also.
Variable Speed of Light
The Theory of Relativity implies that physical constants like c, the speed of light in a vacuum, have remained constant. But at least one study suggests that physical constants, and possibly even the speed of light, have changed as the universe has aged.
"For the first time, scientists have experimentally demonstrated that sound pulses can travel at velocities faster than the speed of light, c. William Robertson's team from Middle Tennessee State University also showed that the group velocity of sound waves can become infinite, and even negative. ... Although such results may at first appear to violate special relativity (Einstein's law that no material object can exceed the speed of light), the actual significance of these experiments is a little different. These types of superluminal phenomena, Robertson et al. explain, violate neither causality nor special relativity, nor do they enable information to travel faster than c. In fact, theoretical work had predicted that the superluminal speed of the group velocity of sound waves should exist. 'The key to understanding this seeming paradox is that no wave energy exceeded the speed of light,' said Robertson."
"A team of researchers from the Ecole Polytechnique Fédérale de Lausanne (EPFL) has successfully demonstrated, for the first time, that it is possible to control the speed of light – both slowing it down and speeding it up – in an optical fiber, using off-the-shelf instrumentation in normal environmental conditions. Their results, to be published in the August 22 issue of Applied Physics Letters, could have implications that range from optical computing to the fiber-optic telecommunications industry." Both slowing down and speeding up of light within a substance other than a vacuum is made possible, because the light travels through the material, and that material affects the speed of light, i.e. a photon hits an electron, which then exits and emits a slightly lower energy photon out in the direction that the original photon was traveling, thus maintaining conservation of momentum. No matter how transparent an object may appear, it radically impacts the speed of the light traveling through it, as demonstrated by the refractive production of a rainbow by a crystal, which Newton himself discovered.
This apparent change in speed can be explained, however, by noting that the constant c refers to the speed of light in a vacuum, i.e., when it is unimpeded. The speed of light when traveling through physical media is, in fact, variable.
"A pair of German physicists claim to have broken the speed of light - an achievement that would undermine our entire understanding of space and time. ... Dr Nimtz told New Scientist magazine: 'For the time being, this is the only violation of special relativity that I know of.'"
Today some physicists are working on hypothesizing how general relativity might have related to the other three forces of nature during the first fraction of a second of the Big Bang. Two of the more commonly studied attempts are string theory and loop quantum gravity, but they have failed to produce any evidence that science mandates a science must have, and both typically take large amounts of work to even conform to what scientists believe. Critics increasingly point out that string theory and loop quantum gravity are largely untestable and unfalsifiable, and thus potentially unscientific under the principles of science advanced by Karl Popper.
Relativity continues to be tested and some physics professors remain skeptical of the theory, such as University of Maryland physics professor Carroll Alley, who served as the principle physicist on the Apollo lunar project.
Political aspects of relativity
Some liberal politicians have extrapolated the theory of relativity to metaphorically justify their own political agendas. For example, Democratic President Barack Obama helped publish an article by liberal law professor Laurence Tribe to apply the relativistic concept of "curvature of space" to promote a broad legal right to abortion. As of June 2008, over 170 law review articles have cited this liberal application of the theory of relativity to legal arguments. Applications of the theory of relativity to change morality have also been common. Moreover, there is an unmistakable effort to censor or ostracize criticism of relativity.
Physicist Robert Dicke of Princeton University was a prominent critic of general relativity, and Dicke's alternative "has enjoyed a renaissance in connection with theories of higher dimensional space-time." Despite being one of the most accomplished physicists in the 20th century, Dicke was repeatedly passed over for a Nobel Prize, and in at least one case Dicke was insulted by the award being granted to others for contributions more properly credited to Dicke.
There has been little recognition by the Nobel Prize committee of either theory of relativity, and particularly scant recognition of the Theory of General Relativity. A dubious 1993 Nobel prize in physics was awarded Hulse and Taylor for supposedly finding the first evidence of gravitational waves in the orbital decay of the binary pulsar PSR1913+16. A close reading of the paper reveals that that is based heavily on assumptions in trying to retrofit the data to the theory.
Government Support for Relativistic research
The Federal Government has funded the building of two gravity wave detectors: The first to test the principle, and the second (upgrade) to actually perform measurements. As a result of this work, on February 11, 2016, the LIGO team reported successful detection of gravitational waves caused by the merging of two black holes.
- Attempts to prove E=mc²
- Counterexamples to Relativity
- Essay:Rebuttal to Counterexamples to Relativity
- Logical Flaws in E=mc²
- Essay:Rebuttal to Logical Flaws in E=mc²
- Quantitative Analysis of Alpha Decay
- Gravitational waves
- What is the experimental basis of Special Relativity?
- Isaacson, Walter (2008). Einstein: His Life and Universe (New York: Simon and Schuster), p. 390. Retrieved from GoogleBooks archive on February 19, 2015.
- "German mathematician who developed the geometrical theory of numbers and who made numerous contributions to number theory, mathematical physics, and the theory of relativity." Hermann Minkowski -- Britannica Online Encyclopedia
- Hermann Minkowski, Biography
- "[T]he German mathematician David Hilbert submitted an article containing the correct field equations for general relativity five days before Einstein."Nobel Prize historical account
- Stephen Hawking, Brief History of Time ("Their measurement had been sheer luck, or a case of knowing the result they wanted to get."). Hawking was being kind. In fact, Eddington excluded data that did not fit his preconceived view. Further discrediting of Eddington's study was published by Earman, J., Glymour, C., Hist. Stud. Phys. Sci. 11, 49-85 (1980), and Collins, H. M., Pinch, T., The Golem: What Everyone Should Know About Science. Cambridge University Press (1993) (as cited in )
- New York Times, July 11, 1935, p23, c8
- For example, Relativity claims that space and time are smooth and continuous, while quantum mechanics suggests otherwise. Relativity also denies action-at-a-distance, while quantum mechanics suggests otherwise. Relativity denies any role for chance, while quantum mechanics is heavily dependent on it.
- http://nobelprize.org/nobel_prizes/physics/laureates/2004/wilczek-lecture.pdf (p. 102)
- http://www.fourmilab.ch/etexts/einstein/specrel/www/ "On the Electrodynamics of Moving Bodies"
- This assumption is commonly restated in this manner. For example, a discussion of hypothetical tachyons talks "about using tachyons to transmit information faster than the speed of light, in violation of Special Relativity."
- Hubble Gravitational Lens Photo
- Gravitational lensing
- Lorentz, H.A. The Einstein Theory of Relativity
- http://archive.salon.com/people/feature/2000/07/06/einstein/index.html See also , where Van Flandern discusses how relativistic corrections might improve GPS accuracy.
- "General Relativity in the Global Positioning System." Neil Ashby, U. of Colorado
- Saturn-Bound Spacecraft Tests Einstein's Theory
- Encounter with Saturn confirms relativity theory
- NASA Gravity Probe B mission page
- Gravity Probe B project page
- There is no reported reliance on relativity by any space probe.
- Hafele-Keating Experiment
- Louis Essen, Electron. Wireless World 94 (1988) 238.
- A. G. Kelly,Reliability of Relativistic Effect Tests on Airborne Clocks, Monograph No.3 Feb.1996, The Institution of Engineers of Ireland, ISBN 1-898012-22-9
- Though relativity did not actually originate from this experiment
- modern magnets are even more powerful and can show the effect more easily.
- http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ "Does the Inertia of a Body Depend its Energy Content?"
- This equation is not related to quantum mechanics.
- Some have suggested that other explanations are possible for this effect. We are trying to track this down.
- Experiments specifically designed to check dilation are rarely conducted any more.
- Einstein's Luck, John Waller, Oxford University Press, ISBN 0-19-860719-9
- The New York Times, Nov. 10, 1919
- How did an eclipse help make Albert Einstein famous
- How Albert Einstein became a celebrity
- "The public's mind was blown by the results, effectively turning Albert Einstein into a household name and cementing the concept of general relativity into physics books."
- http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_GRelativity_1916.pdf "The Foundation of the General Theory of Relativity"
- For example, this was taught as recently as in the 1991 edition of the Encyclopedia Britannica.
- James Glanz and Dennis Overbye, "Cosmic Laws Like Speed of Light Might Be Changing, a Study Finds," August 15, 2001.
- See, for example, Not Even Wrong, by Peter Woit
- Tribe, acknowledging help by Obama, argued that the Constitution should be interpreted to establish a right to federally funded abortion and that, more generally, Roe v. Wade does not go far enough. They insisted that a relativistic "curvature of space" could achieve this result by expanding application of the Constitution based on its impact on personal choice. "The Roe v. Wade opinion ignored the way in which laws regulating pregnant women may shape the entire pattern of relationships among men, women, and children. It conceptualized abortion not in terms of the intensely public question of the subordination of women to men through the exploitation of pregnancy, but in terms of the purportedly private question of how women might make intimately personal decisions about their bodies and their lives. That vision described a part of the truth, but only what might be called the Newtonian part. ... [A] change in the surrounding legal setting can constitute state action that most threatens the sphere of personal choice. And it is a 'curved space' perspective on how law operates that leads one to focus less on the visible lines of legal force and more on how those lines are bent and directed by the law's geometry." Laurence H. Tribe, The Curvature of Constitutional Space: What Lawyers Can Learn from Modern Physics, 103 Harv. L. Rev. 1, 16-17 (1989).
- Search conducted by User:Aschlafly in the LEXIS database "US Law Reviews and Journals, Combined," conducted June 1, 2008.
- "Mistakenly, in the minds of many, the theory of relativity became relativism."
- Although the liberally biased Wikipedia contains lengthy criticisms of the subjects of many entries, and even though publications like The Economist recognize the lack of scientific satisfaction in the theory (see, e.g., "Weighing the Universe," The Economist (Jan. 25, 2007)), Wikipedia's entry on Theory of Relativity omits one word of criticism.
- "Initially a popular alternative to General Relativity, the Brans-Dicke theory lost favor as it became clear that omega must be very large-an artificial requirement in some views. Nevertheless, the theory has remained a paradigm for the introduction of scalar fields into gravitational theory, and as such has enjoyed a renaissance in connection with theories of higher dimensional space-time."
- Weisberg, Joel M.; Taylor, Joseph H. (2003), "The Relativistic Binary Pulsar B1913+16"", in Bailes, M.; Nice, D. J.; Thorsett, S. E., Proceedings of "Radio Pulsars," Chania, Crete, August, 2002, ASP Conference Series
- The Einstein Theory of Relativity, by H.A. Lorentz.
- Relativity Science Calculator - Learn Special Relativity Mathematics The mathematics of special relativity presented in as simple and comprehensive manner possible within philosophical and historical contexts.
- Relativity Science Calculator - Philosophic Question: are clocks and time separable?
- Relativity Science Calculator - Twin Clock Paradox | 0.867177 | 3.639491 |
Physical characteristics Size comparison with Earth Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is Mapping of Venus The Venusian surface was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century.
Venus was the goddess of agriculture, but was later identified with the Greek goddess Aphrodite and became known as a goddess of love. Surface Hemispheric view of Venus produced by Magellan. Pancake Domes on Venus in 3-D view.
The surface of Venus is a rocky, dusty, waterless expanse of mountains, canyons, and plains. Most of Venus is relatively "new" lava plains about million years old, marked by volcanic features and some impact craters.
There are two highland "continent" features called Ishtar Terra and Aphrodite Terra. The planet appears to be a barren desert covered by slab-like rocks and dust. Edit A north pole of Venus Venus is an unlikely place to find living things.
The sulphuric acid is not the problem—there are bacteria on Earth which excrete and thrive in sulphuric acid. The immense pressure is not a problem—although it would splat you flat, there are creatures at the bottom's of the Earth 's oceans who survive much greater pressures.
These creatures are not crushed by the immense pressure since they are adapted to these conditions and the pressure inside their cells is just as great, thus counterbalancing the external pressure upon them.
They also have special enzymes, since certain chemical reactions those involving a tiny increase in volume are inhibited at such pressures. The problem is the immense temperature. Even if liquid water existed under pressure, the heat would tend to disrupt complex molecules.
However, the clouds of Venus are cool and it is likely that certain bacteria can survive and grow within the clouds. We also must ask ourselves if conditions are so harsh deep down inside the planet's crust. However, even if a place can be found where bacteria-like organisms could thrive, this does not mean that they would have evolved there—the temperatures really do seem prohibitively high.
Magellan Edit Mapping Venus' surface in orbit of Magellan. The Magellan spacecraft was the first planetary explorer to be launched by a space shuttle when it was carried aloft by the shuttle Atlantis from Kennedy Space Center in Florida on May 4, Atlantis took Magellan into low Earth orbit, where it was released from the shuttle's cargo bay and fired by a solid-fuel motor called the Inertial Upper Stage IUS on its way to Venus.
Magellan looped around the Sun one-and-a-half times before arriving at Venus on August 10, A solid-fuel motor on the spacecraft then fired, placing Magellan into a near-polar elliptical orbit around Venus.
The spacecraft carried a sophisticated imaging radar, which was used to make the most highly detailed map of Venus ever captured during its four years in orbit around Venus from to After concluding its radar mapping, Magellan also made global maps of Venus's gravity field.
Flight controllers then tested a new maneuvering technique called aerobraking, which uses a planet's atmosphere to slow or steer a spacecraft. The spacecraft made a dramatic plunge into the thick, hot Venusian atmosphere on October 12,and was crushed by the pressure of Venus's atmosphere.
Magellan's signal was lost at Pacific Daylight Time that day. The Magellan mission was divided up into "cycles" with each cycle lasting days the time necessary for Venus to rotate once under the Magellan orbit.Venus is the second planet from the Sun, orbiting it every Earth days.
It has the longest rotation period of any planet in the Solar System, and, unusually, rotates in the opposite direction to most other planets.
It has no natural satellite. Venus is the second planet from the Sun. Venus is the hottest planet in the Solar System, though it is not the closest to the Sun, in which said title goes to the planet Mercury. The reason that this planet is hot is due to Venus' dense r-bridal.com of Sattelites: None (1 hypothetical satellite called Neith).
Venus is the second planet from the Sun, orbiting it every Earth days.
It has the longest rotation period ( days) of any planet in the Solar System and rotates in the opposite direction to most other planets (meaning the Sun would rise in the west and set in the east).
Whichever you prefer, here is a list of them in the order they appear in the solar system. news; Below is a brief overview of the eight The second planet from the sun, Venus is terribly.
Introduction Venus is the second planet from the Sun and our closest planetary neighbor. Similar in structure and size to Earth, Venus spins slowly in the opposite direction from most planets. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead.
Venus orbits our Sun, a star. Venus is the second closest planet to the sun at a distance of about 67 million miles ( million km). | 0.867092 | 3.739628 |
The view in the infrared is strikingly different from that in visible light. With dust obscuring the view far less, astronomers can learn much more about how stars in the nebula form and develop in their first few million years of life.
NGC 6334 is one of the most active nurseries of massive stars in our galaxy and lies toward the heart of the Milky Way, 5500 light-years from Earth in the constellation of Scorpius (the Scorpion).
VISTA is the world's largest survey telescope. It works at infrared wavelengths, seeing right through much of the dust that is such a beautiful but distracting aspect of the nebula, and revealing objects hidden from the sight of visible light telescopes. Visible light tends to be scattered and absorbed by interstellar dust, but the dust is nearly transparent to infrared light.
This is an infrared view of the Cat's Paw Nebula (NGC 6334) taken by VISTA. The images were taken through Y, J and Ks filters (shown as blue, green and red respectively) and the exposure time was five minutes per filter. The field of view is about one degree across.
(Photo Credit: ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit)
VISTA has a main mirror that is 4.1 meters across and it is equipped with the largest infrared camera on any telescope. It shares the spectacular viewing conditions with ESO's Very Large Telescope (VLT). With this powerful instrument at their command, astronomers were keen to see the birth pains of the big young stars in the Cat's Paw Nebula, some nearly ten times the mass of the Sun.
The very wide field of view offered by the VISTA telescope allows the whole star-forming region to be imaged in one shot with much greater clarity than ever before.
The VISTA image is filled with countless stars of our Milky Way galaxy overlaid with spectacular tendrils of dark dust that are seen here fully for the first time. The dust is sufficiently thick in places to block even the near-infrared radiation to which VISTA's camera is sensitive.
In many of the dusty areas, such as those close to the center of the picture, features that appear orange are apparent — evidence of otherwise hidden active young stars and their accompanying jets. Further out though, slightly older stars are laid bare to VISTA's vision, revealing the processes taking them from their first nuclear fusion along the unsteady path of the first few million years of their lives. | 0.888934 | 3.82212 |
Newswise — A team of astronomers has unveiled a striking new image of the Orion Molecular Cloud (OMC) – a bustling stellar nursery teeming with bright, young stars and dazzling regions of hot, glowing gas.
The researchers used the National Science Foundation’s (NSF) Green Bank Telescope (GBT) in West Virginia to study a 50 light-year long filament of star-forming gas that is wending its way through the northern portion of the OMC known as Orion A.
The GBT rendered this image by detecting the faint radio signals naturally emitted by molecules of ammonia that suffuse interstellar clouds. Scientists study these molecules to trace the motion and temperature of vast swaths of star-forming gas.
These observations are part of the first data release from a large campaign known as the Green Bank Ammonia Survey. Its purpose is to map all of the star-forming ammonia and other key tracer molecules in a massive structure known as the Gould Belt.
The Gould Belt is an extended ribbon of bright, massive stars stretching about 3,000 light-years in an arc across the sky. This first release covers four distinct Gould Belt clouds, one located in Taurus, one in Perseus, one in Ophiuchus, and Orion A North in Orion.
“We hope to use these data to understand better how large clouds of gas in our galaxy collapse to form new stars,” said Rachel Friesen, one of the collaboration’s co-principal investigators and, until 31 May 2017, a Dunlap Fellow at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto in Canada. “The new data are critical to assessing whether certain gas clouds and filaments are stable and enduring features or if they are undergoing collapse and forming new stars.”
Prior ammonia observations by many of the survey’s co-authors have targeted smaller portions of similar star-forming clouds. In these individual studies, the researchers identified sharp transitions in the amount of turbulence between the larger cloud and the smaller-scale star-forming cores, studied the stability against gravitational collapse of the gas within a young protocluster, and investigated how mass builds up along gas filaments and flows into stellar cluster-forming regions.
"These data provide a unique view of the cold dense gas involved in forming stars like our sun," said Jaime E. Pineda, the collaboration's other co-principal investigator, with the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany. "We hope they can also help us determine how much rotation is present in the regions that will form stars; this is crucial to understand how protoplanetary disks are formed."
The new GBT image is combined with an infrared one taken with NASA’s Wide-field Infrared Survey Explorer (WISE) telescope. The composite image illustrates how star-forming gas in this region relates to the bright stars and dark, dusty regions of the nebula.
The 100-meter GBT, which is located in the National Radio Quiet Zone, is exquisitely sensitive and uniquely able to study the molecular composition of star-forming clouds and other objects in the cosmos. Future observations of the Gould Belt will provide greater insights into the conditions that give rise to stars like our sun and planets like Earth.
The Green Bank Observatory (GBO) is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc.
# # #
This research is presented in a paper titled “The Green Bank Ammonia Survey (GAS): First results of NH3 mapping the Gould Belt,” R. Friesen and J. Pineda et al. appearing in the Astrophysical Journal [http://apj.aas.org].
Contact: Mike Holstine
MEDIA CONTACTRegister for reporter access to contact details
Astrophysical Journal Supplement, June-2017 | 0.924952 | 3.913786 |
Image credit: ESA
ESA’s Integral gamma-ray observatory has resolved the diffuse glow of gamma rays in the centre of our Galaxy and has shown that most of it is produced by a hundred individual sources.
Integral’s high sensitivity and pointing precision have allowed it to detect these celestial objects where all other telescopes, for more than thirty years, had seen nothing but a mysterious, blurry fog of gamma rays…
During the spring and autumn of 2003, Integral observed the central regions of our Galaxy, collecting some of the perpetual glow of diffuse low-energy gamma rays that bathe the entire Galaxy.
These gamma rays were first discovered in the mid-1970s by high-flying balloon-borne experiments. Astronomers refer to them as the ‘soft’ Galactic gamma-ray background, with energies similar to those used in medical X-ray equipment.
Initially, astronomers believed that the glow was caused by interactions involving the atoms of the gas that pervades the Galaxy. Whilst this theory could explain the diffuse nature of the emission, since the gas is ubiquitous, it failed to match the observed power of the gamma rays. The gamma rays produced by the proposed mechanisms would be much weaker than those observed. The mystery has remained unanswered for decades.
Now Integral’s superb gamma-ray telescope IBIS, built for ESA by an international consortium led by Principal Investigator Pietro Ubertini (IAS/CNR, Rome, Italy), has seen clearly that, instead of a fog produced by the interstellar medium, most of the gamma-rays are coming from individual celestial objects. In the view of previous, less sensitive instruments, these objects appeared to merge together.
In a paper published today in Nature, Francois Lebrun (CEA Saclay, Gif sur Yvette, France) and his collaborators report the discovery of 91 gamma-ray sources towards the direction of the Galactic centre. Lebrun’s team includes Ubertini and seventeen other European scientists with long-standing experience in high-energy astrophysics. Much to the team’s surprise, almost half of these sources do not fall in any class of known gamma-ray objects. They probably represent a new population of gamma-ray emitters.
The first clues about a new class of gamma-ray objects came last October, when Integral discovered an intriguing gamma-ray source, known as IGRJ16318-4848. The data from Integral and ESA’s other high-energy observatory XMM-Newton suggested that this object is a binary system, probably including a black hole or neutron star, embedded in a thick cocoon of cold gas and dust. When gas from the companion star is accelerated and swallowed by the black hole, energy is released at all wavelengths, mostly in the gamma rays.
However, Lebrun is cautious to draw premature conclusions about the sources detected in the Galactic centre. Other interpretations are also possible that do not involve black holes. For instance, these objects could be the remains of exploded stars that are being energised by rapidly rotating celestial ‘powerhouses’, known as pulsars.
Observations with another Integral instrument (SPI, the Spectrometer on Integral) could provide Lebrun and his team with more information on the nature of these sources. SPI measures the energy of incoming gamma rays with extraordinary accuracy and allows scientist to gain a better understanding of the physical mechanisms that generate them.
However, regardless of the precise nature of these gamma-ray sources, Integral’s observations have convincingly shown that the energy output from these new objects accounts for almost ninety per cent of the soft gamma-ray background coming from the centre of the Galaxy. This result raises the tantalising possibility that objects of this type hide everywhere in the Galaxy, not just in its centre.
Again, Lebrun is cautious, saying, “It is tempting to think that we can simply extrapolate our results to the entire Galaxy. However, we have only looked towards its centre and that is a peculiar place compared to the rest.”
Next on Integral’s list of things to do is to extend this work to the rest of the Galaxy. Christoph Winkler, ESA’s Integral Project Scientist, says, “We now have to work on the whole disc region of the Galaxy. This will be a tough and long job for Integral. But at the end, the reward will be an exhaustive inventory of the most energetic celestial objects in the Galaxy.”
Original Source: ESA News Release | 0.834407 | 4.02731 |
Crescent ♉ Taurus
Moon phase on 26 May 2071 Tuesday is Waning Crescent, 26 days old Moon is in Aries.Share this page: twitter facebook linkedin
Previous main lunar phase is the Last Quarter before 4 days on 22 May 2071 at 06:18.
Moon rises after midnight to early morning and sets in the afternoon. It is visible in the early morning low to the east.
Lunar disc appears visually 0.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1884" and ∠1894".
Next Full Moon is the Strawberry Moon of June 2071 after 17 days on 12 June 2071 at 17:36.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 26 days old. Earth's natural satellite is moving from the second to the final part of current synodic month. This is lunation 882 of Meeus index or 1835 from Brown series.
Length of current 882 lunation is 29 days, 8 hours and 46 minutes. It is 1 hour and 42 minutes longer than next lunation 883 length.
Length of current synodic month is 3 hours and 58 minutes shorter than the mean length of synodic month, but it is still 2 hours and 11 minutes longer, compared to 21st century shortest.
This lunation true anomaly is ∠313.2°. At the beginning of next synodic month true anomaly will be ∠334°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
7 days after point of apogee on 18 May 2071 at 23:14 in ♑ Capricorn. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 4 days, until it get to the point of next perigee on 31 May 2071 at 00:58 in ♋ Cancer.
Moon is 380 477 km (236 417 mi) away from Earth on this date. Moon moves closer next 4 days until perigee, when Earth-Moon distance will reach 360 783 km (224 180 mi).
1 day after its descending node on 24 May 2071 at 23:39 in ♓ Pisces, the Moon is following the southern part of its orbit for the next 11 days, until it will cross the ecliptic from South to North in ascending node on 6 June 2071 at 13:14 in ♍ Virgo.
16 days after beginning of current draconic month in ♎ Libra, the Moon is moving from the second to the final part of it.
9 days after previous South standstill on 17 May 2071 at 00:17 in ♑ Capricorn, when Moon has reached southern declination of ∠-18.342°. Next 4 days the lunar orbit moves northward to face North declination of ∠18.383° in the next northern standstill on 30 May 2071 at 20:30 in ♊ Gemini.
After 2 days on 29 May 2071 at 11:17 in ♊ Gemini, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.83659 | 3.248285 |
Mars can break your heart, and it did the job exquisitely today. For all the splendor of the first pictures from the surface of the moon, it was clear that the place was a big, dead rock — and that it always had been. But every image every orbiter and lander sends back from Mars makes it clearer and clearer that our close neighbor was a near-miss planet, a place that coulda been a contender. It had abundant water and a protective atmosphere and — who knows? — even sentient creatures that might have kept us company in what otherwise has been a very silent universe.
The images the Curiosity rover just beamed home are more poignant reminders of the planetary beauty Mars surely was. For a long time, the goal of Mars probes has been to confirm that what appear to be dry ocean basins, seabeds and river trails were once filled with water. On-the-ground surveys by the Spirit and Opportunity rovers sealed that deal when they found hematites, salt and other minerals that form only or largely in watery environments. So it was no surprise that Curiosity would find similar proof. Indeed, the ship’s landing site, Gale Crater, was chosen explicitly because it was likely once submerged. A delta-shaped ground formation known as an alluvial fan even reveals how the water flowed.
But the newest pictures are striking — and strangely dislocating — all the same. They reveal nothing more or less than smooth, water-polished pebbles, some as big as a golf ball and others as small as a grain of sand. You’ve seen them in every stream you ever played in as a child; you’ve collected them in paper cups. And now they’ve shown up on Mars.
The size and shape of the pebbles suggest that the water was moving at about 3 ft. (1 m) per second — a brisk, vigorous flow — and that it was ankle- to knee-deep, according to Curiosity scientist William Dietrich of the University of California, Berkeley. “Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them,” he said in a NASA release. “This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it.”
Some of the pebbles are loose and separate; others are mixed into a dry conglomerate that is probably the remains of the ancient streambed. Project scientist John Grotzinger compares that mix to the composite chunks that get dislodged when a jackhammer meets a city sidewalk. The stream was probably fed by a channel in the alluvial fan that the investigators have named Peace Vallis. Still to come are closer investigations of the precise composition of the pebbles and soil, not to mention two years of tooling around Gale Crater and the base of Mount Sharp that rises in its center, which is carved with its own ancient waterways.
The scientists do not expect to find signs of ancient biology among the pebbles they’ve discovered. It’s not impossible for life to take hold in water moving so fast, but “it is not our top choice,” says Grotzinger. But if the same kinds of waterways on Earth indicate anything, it’s that just downstream from the churning currents, the water can can feed into calm, nearly amniotic pools. And there’s no telling what kind of Martian life might once have called such places home. | 0.804685 | 3.820288 |
New infrared images of Uranus show details not seen before. Credit: NASA/ESA/L. A. Sromovsky/P. M. Fry/H. B. Hammel/I. de Pater/K. A. Rages
Here’s the scene: a thick, tempestuous atmosphere with winds blowing at a clip of 900 km/h (560 mph); massive storms that would engulf continents here on Earth, and temperatures in the -220 C (-360 degree F) range. Sounds like a cold Hell, but this is the picture emerging of the planet Uranus, revealed in new high-resolution infrared images from the Keck Observatory in Hawaii, exposing in incredible detail the bizarre weather of a planet that was once thought to be rather placid.
“My first reaction to these images was ‘wow’ and then my second reaction was ‘WOW,'” said Heidi Hammel, a co-investigator on the new observations. “These images reveal an astonishing amount of complexity in Uranus’ atmosphere. We knew the planet was active, but until now much of the activity was masked by noise in our data.”
Voyager 2’s view of Uranus. Credit: NASA
With its beautiful blue atmosphere, Uranus can seem rather tranquil at first glance. Even the flyby of Voyager 2 in 1986 revealed a rather “bland” blue ball. But coming into focus now with the new are large weather systems, and even though they are probably much less violent than storms on Earth, the weather on Uranus is just…bizarre.
“Some of these weather systems,” said Larry Sromovsky, from the University of Wisconsin-Madison who led the new study using the Keck II telescope, “stay at fixed latitudes and undergo large variations in activity. Others are seen to drift toward the planet’s equator while undergoing great changes in size and shape. Better measures of the wind fields that surround these massive weather systems are the key to unraveling their mysteries.”
Sromovsky, Hammel and their colleagues are using new infrared techniques to deliver some of the “most richly detailed views of Uranus yet obtained by any instrument on any observatory. No other telescope could come close to producing this result,” Sromovsky said.
What they are seeing are previously undetected, small but widely distributed weather feature, and they hope the movements of these features can help make sense of the planet’s odd pattern of winds.
They observed a scalloped band of clouds just south of Uranus’ equator and a swarm of small convective features in the north polar regions of the planet. Features like this don’t seem to be in the southern polar regions, but are similar to the types of “popcorn” –type clouds seen on Saturn. Uranus’ north pole is not visible from Earth night now, but when it does come into view, the researchers wouldn’t be surprised to see a polar vortex feature similar to what has been seen at Saturn’s south pole.
The driver of these features must be solar energy because there is no other detectable internal energy source.
“But the Sun is 900 times weaker there than on Earth because it is 30 times further from the Sun, so you don’t have the same intensity of solar energy driving the system,” said Sromovsky. “Thus the atmosphere of Uranus must operate as a very efficient machine with very little dissipation. Yet the weather variations we see seem to defy that requirement.”
One possible explanation, is that methane is pushed north by an atmospheric conveyor belt toward the pole where it wells up to form the convective features visible in the new images. The phenomena may be seasonal, the team said, but they are still working on trying to put together a clear seasonal trend in the winds of Uranus.
“Uranus is changing,” he said, “and there is certainly something different going on in the two polar regions.”
The images were released at the American Astronomical Society’s Division for Planetary Sciences meeting taking place this week.
Source: University of Wisconsin-Madison | 0.870326 | 3.825615 |
It’s a happy day when astronomers figure out what’s up with an enormous space blob — and the answer doesn’t imply the immediate destruction of humanity.
A cosmological simulation of a Lyman alpha blob that traces the evolution of gas and dark matter from a central star-forming region. Image: J.Geach/D.Narayanan/R.Crain
You probably haven’t heard of SSA22-Lyman-alpha blob 1, but rest assured, telescope jockeys have been scratching their heads over it for years. Now, a team of astronomers has finally figured out what’s happening inside the blob that’s causing it to light up.
Lyman-alpha blobs, or LABs, are clouds of cold hydrogen gas spanning hundreds of thousands of light years in the most distant reaches of the known universe. They get their name from Lyman-alpha radiation, a distinct wavelength of UV light that’s emitted when electrons in hydrogen atoms jump from one energy state to another. Because LABs are found billions of light years away, their radiation signature is redshifted all the way down to the optical by the time it reaches our telescopes. To us, the blobs look like weird smudges of colour suspended on the edge of time.
SSA22-Lyman-alpha blob 1 (LAB-1) was the first such blob astronomers discovered, all the way back in 2000. To date, it remains on of the largest LABs ever spotted, but like most of its brethren, the blob’s tremendous distance — 11.5 billion light years from Earth — has made it difficult to study. Nevertheless, there’s reason to think this blob is special.
Lyman-alpha blob (LAB-1) pictured at the centre is one of the largest known objects in the universe. Because of its distance, the blob’s UV emissions get stretched on their journey through space and appear green to our telescopes. Image: ESO/M. Hayes
“[LAB-1] happens to be at the centre of a large protocluster — a region of the universe that’s very dense,” astronomer Jim Geach of the University of Hertfordshire told Gizmodo. “This region will eventually collapse into a large cluster. So the fact that we see this large blob close to the centre suggests it has something to do with the formation of large galaxies.”
To test that hypothesis, Geach and has collaborators turned to the Atacama Large Millimetre Array (ALMA), a radio telescope with unparalleled ability to resolve sub millimetre emissions, a form of long wavelength radiation used to study cool gases in faraway corners of space. Previously, other telescopes had detected sub millimetre emissions coming from the centre of LAB-1, but with ALMA’s greater seeing power, Geach was finally able to resolve the source. It turned out to be two.
“We found that this single [emission] breaks up into several clumps, corresponding to different galaxies,” Geach said.
In fact, the emission comes from to two large, central galaxies on the verge of smashing together. And there’s something else. Like hungry piranhas waiting to feast on the carnage, a swarm of smaller galaxies appear to be chilling around the perimeter. “We’re basically seeing the formation of the centre of a cluster of galaxies, right when all the action is taking place,” Geach said.
But wait, didn’t this intergalactic mosh pit look like nothing more than slimy green jelly for nearly 20 years? Geach thinks he knows why. Using a sophisticated computer model, he was able to reproduce the blob’s Lyman-alpha signature, if UV light produced during star formation was scattered off cold hydrogen gas in its surroundings.
Infographic explaining what happens when a Lyman-alpha blob shines. Image: ESO/J. Geach
Geach’s discovery, which has been accepted for publication in the Astrophysical Journal, has some major implications for astrophysics. If other LABs turn out to be powered by galactic cluster formation, too, then these blobs could offer an unprecedented window into the assembly of enormous structures in the early universe. They may also be one of our best opportunities to shed some much-needed light on dark matter.
“In our picture of galaxy formation, we think galaxies form in these large, dark matter haloes,” Geach said. “The stuff you see in galaxies is the stars, but a lot of the key astrophysics in galaxy formation is occurring in the immediate region around galaxies. Lyman alpha photons are scattering light in that dark matter, and giving us insight into its structure.”
The next step will be to observe other LABs with ALMA, and determine whether similar processes are playing out at the centre. Still, just knowing that LAB-1 can be explained by perfectly natural astrophysical processes is great news for Earthlings. If all that light was coming from an 11 billion year-old civilisation with a trillion fusion-powered warships, I’m not sure we’d be safe in this universe. | 0.863223 | 3.998461 |
Telescope sweep in stunning detail
A high-tech telescope in the West Australian outback has produced incredible new pictures of our Universe.
The GaLactic and Extragalactic All-sky MWA, or ‘GLEAM’ survey, has produced a catalogue of 300,000 galaxies observed by the Murchison Widefield Array (MWA), a $50 million radio telescope located at a remote site northeast of Geraldton.
It is the first radio survey to obtain images of the sky in such amazing technicolour.
“The human eye sees by comparing brightness in three different primary colours – red, green and blue,” said Dr Natasha Hurley-Walker, from Curtin University and the International Centre for Radio Astronomy Research (ICRAR).
“GLEAM does rather better than that, viewing the sky in 20 primary colours.”
GLEAM is a large-scale, high-resolution survey of the radio sky observed at frequencies from 70 to 230 MHz, observing radio waves that have been travelling through space - some for billions of years.
“Our team are using this survey to find out what happens when clusters of galaxies collide,” Dr Hurley-Walker said.
“We’re also able to see the remnants of explosions from the most ancient stars in our galaxy, and find the first and last gasps of supermassive black holes.”
MWA Director Associate Professor Randall Wayth, from Curtin University and ICRAR, said GLEAM is one of the biggest radio surveys of the sky ever assembled.
“The area surveyed is enormous,” he said.
“Large sky surveys like this are extremely valuable to scientists and they’re used across many areas of astrophysics, often in ways the original researchers could never have imagined,” Associate Professor Wayth said.
The GLEAM survey with the MWA is another step on the path to SKA-low; the low frequency part of the international Square Kilometre Array (SKA) radio telescope to be built in Australia in coming years.
The research paper on the survey is accessible here, and the team has created an interactive visualisation of their findings, available below. | 0.859909 | 3.472782 |
NASA released a spooky image recently of two galaxies which are merging, nearly 700 million light years away. The image is notable, not only because of the absolute chaos that must be happening as the result of billions of stars swirling about in a cosmic superstorm, but because the image looks like a ghostly human face. The Hubble space telescope captured the image of the two ring galaxies colliding. Although this display will last another 100 million years for us, the formation ended about 600 million years ago in that region, because of space and time.
According to NASA:
Each “eye” is the bright core of a galaxy, one of which slammed into another. The outline of the face is a ring of young blue stars. Other clumps of new stars form a nose and mouth. The entire system is catalogued as Arp-Madore 2026-424 (AM 2026-424), from the Arp-Madore “Catalogue of Southern Peculiar Galaxies and Associations.”
NASA via Hubblesite.com
Although galaxy collisions are common—especially back in the young universe—most of them are not head-on smashups, like the collision that likely created this Arp-Madore system. The violent encounter gives the system an arresting “ring” structure for only a short amount of time, about 100 million years. The crash pulled and stretched the galaxies’ disks of gas, dust, and stars outward. This action formed the ring of intense star formation that shapes the nose and face.
This came after NASA released the famous Halloween picture that we covered before: | 0.871929 | 3.235822 |
Space rocks are a hot commodity lately; namely asteroids. Not only have several skimmed past the Earth within uncomfortably-close proximities recently, but researchers eventually want to grab samples of nearby asteroids to obtain a deeper understanding of their compositions.
Image Credit: NASA/JPL-Caltech
Planetary scientists and astronomers alike refer to asteroids residing closes to Earth in the solar system as Near-Earth Asteroids (NEAs), and as of October 3rd, experts believe say there are as many as 16,729-known NEAs.
The latter range in size and most measure under 1 kilometer in diameter, but the number of unknown NEAs is what worries most experts because it's what we can't see that pose the highest threat to Earth.
Astronomy aficionados are familiar with the back-and-forth banter between researchers, with some claiming there are more undiscovered space rocks in our neighborhood than we give credit for, but planetary scientist Alan W. Harris seems convinced of just the opposite.
His latest calculations reveal how we might be over-estimating the number of undiscovered NEAs out there, and he plans to unveil his findings at the 49th annual Division for Planetary Sciences meeting, which takes place in Provo, Utah this week.
Many initial estimations, including some that Harris himself made, could be flawed because of a ‘rounding error’ in the algorithms used. Correcting that oversight reportedly yields notable changes to the amount of possible undiscovered NEAs.
Uncorrected, the error could drive one to think that more than 100 unidentified NEAs measuring more than 1 kilometer in diameter lurk in the shadows around us. Upon fixing the mistake, the numbers highlight that there are just 30-40 unknown NEAs of this flavor residing in our planet’s neighborhood.
If that wasn’t enough to raise some eyebrows, it’s fascinating to point out that Harris’ corrected figures agree with NEA estimates given by other entities. Interestingly, these estimates are unrelated to Harris’ and use entirely separate algorithmic calculations to achieve their numbers; that said, he might be onto something here.
There’s no sure-fire way to know precisely how many undiscovered NEAs reside in the solar system because they’re… well… undiscovered. That said, all we can do is predict their existence based on how many that we’ve found so far within a confined chunk of space.
It should be interesting to see how the scientific community responds to Harris’ update, and whether it will have any implications for the way we study the solar system. | 0.849241 | 3.587459 |
A stunning new view of the Andromeda galaxy reveals an unexpected pair of supermassive black holes that researchers say are in close orbit around each other.
When they caught the black holes on camera, NASA's Chandra X-ray Observatory and ground-based optical telescopes were photographing the nearby Andromeda galaxy, also known as Messier 31 (M31). This spiral galaxy is about 2.5 million light-years from Earth, making it our Milky Way's closest neighbor.
The new images revealed an unusual source of radiation known as J004527.30+413254.3 (or J0045+41), which researchers thought was located within Andromeda but is instead a whopping 2.6 billion light-years away and contains a pair of monster black holes that act "as a cosmic bomb," researchers said in a statement. [Andromeda Galaxy Photos: Amazing Pictures of M31]
The estimated total mass for the two giant black holes is about 2 hundred million times that of the sun, according to the statement. The black holes are believed to be in close orbit around each other and may even be "the most tightly coupled pair of supermassive black holes ever seen," the researchers said.
"We were looking for a special type of star in M31 and thought we had found one," lead author Trevor Dorn-Wallenstein, a researcher from the University of Washington in Seattle, said in the statement. "We were surprised and excited to find something far stranger!"
Previously, scientists thought J0045+41 was a different kind of object within M31. Earlier observations showed periodic variations in the optical light from J0045+41, which researchers initially classified as a pair of stars that orbited around each other approximately once every 80 days.
The new data, however, shows that the repeating variations in the light from J0045+41 are actually the result of a pair of orbiting supermassive black holes, located much farther from Earth than previously thought.
In addition to the Chandra X-ray Observatory, the recent observations used data from the Gemini North telescope in Hawaii and the California Institute of Technology's Palomar Observatory. Astronomers used the ground-based telescopes' observations to estimate the location and velocities of the supermassive black holes.
The optical data from the Palomar Transient Factory also revealed several periodic variations in the light from J0045+41, including ones at about 80 and 320 days, according to the statement.
"This is the first time such strong evidence has been found for a pair of orbiting giant black holes," co-author Emily Levesque, a researcher from the University of Washington, said in the statement.
The black holes are believed to orbit each other with a separation of only a few hundred times the distance between the Earth and the sun. At this distance, which is less than one hundredth of a light-year, the two black holes are in orbits that bring them exceptionally close together, the researchers said.
This type of system likely formed following a galaxy merger that occurred billions of years ago. In this scenario, the two galaxies that merged would have each contained a supermassive black hole of its own, according to the study.
Currently, the two giant black holes emit gravitational waves as they draw closer together. Eventually, the black holes are expected to collide, the researchers said.
"We're unable to pinpoint exactly how much mass each of these black holes contains," co-author John Ruan, a researcher from the University of Washington, said in the statement. "Depending on that, we think this pair will collide and merge into one black hole in as little as 350 years or as much as 360,000 years."
Their findings were published Nov. 20 in The Astrophysical Journal. | 0.890203 | 3.776825 |
fireballs.ndc.nasa.gov). Image Credit: James M. Thomas
148! I kid you not. NASA's All Sky Fireball Network (fireballs.ndc.nasa.gov) managed to determine that 148 of the fireballs it recorded during the dark hours of August 12th UTC were, in fact, from the Perseid meteor shower. What a jump from the counts recorded in the mid- and upper-teens on the two previous evenings. I guess there can be little doubt that Earth has experienced, and possibly still is experiencing, the maximum of this annual shower. Of course, we should note that these observations were gathered from multiple locations. The Network currently has eight video cameras, with two in New Mexico and the rest spread over Alabama, Georgia and South Carolina. For these Network observations, a fireball is defined as any meteor with a brightness equal to Venus or brighter.
But even with the maximum possibly waning, there is still time to see some Perseids. The shower runs from July 23rd through August 20th. Whether fireball or run-of-the-mill meteor, you are sure to see at least a few Perseids if you observe from a reasonably dark sky.
Perseids enter the atmosphere at about 59 km/second (37 miles/second) and are yellow in color. The Perseid shower occurs each year when Earth passes through the debris trail of Periodic Comet 109P/Swift-Tuttle, also called Comet 1862 III, discovered on July 16, 1862 by American astronomer Lewis A. Swift and then independently discovered three days later by American astronomer Horace Parnell Tuttle. Perseid meteors appear to radiate from a point in the constellation of Perseus (Right Ascension 03hrs 04min, Declination +58°). This year, the zenithal hourly rate (from a single location) is expected to reach 60.
To learn more about meteors, comets, and asteroids, check out these URLs.
NASA's All Fireball Network (fireballs.ndc.nasa.gov), part of NASA's Meteoroid Environment Office, www.nasa.gov/offices/meo .
Asteroids, Comets, Meteorites (a NASA Asteroid Watch article): www.jpl.nasa.gov/asteroidwatch/asteroids-comets.cfm
NASA's Near-Earth Object (NEO) Program coordinates NASA-sponsored efforts to detect, track and characterize potentially hazardous asteroids and comets that could approach the Earth. To learn more, visit the home page of NASA's Near-Earth Object Program: neo.jpl.nasa.gov . | 0.809392 | 3.364712 |
The announcement of the discovery of two gas clouds that have formed in the first minutes after the Big Bang was published in Science; the clouds composition confirms theoretical predictions. The leading author of the study is the Italian Michele Fumagalli, from the University of California Santa Cruz, with whom we had a chat and to whom we asked for some clarifications.The discovery is the result of a clever observation technique and excellent performance of the spectrograph at the Hawaiian Observatory WM Keck. Fumagalli and colleagues analyzed two cases in which the light travelling from a very distant quasar crossed a gas cloud along its path.The cloud has left its indelible mark in the light spectrum of the quasar, and this has enabled researchers to trace back the elements that made up the gas cloud, revealing a perfect harmony with the primitive composition of the Universe as predicted by the Big Bang cosmological model.
Was this the result of a fortuitous coincidence, Fumagalli?
Not at all. We are studying in detail the composition of many similar gas clouds. We already knew there was some hydrogen in that part of the universe. The unexpected discovery was the absence of heavy elements observed by using new high-quality spectra of the Keck telescope.
Given the considerable success, I guess you're already looking around for other clouds similar to the two identified.
Absolutely. We're sifting through hundreds of quasars with the same technique and most likely we will be able to find some other clouds with properties similar to the two we have found.
The importance of this discovery has been emphasized by many. Is this due to the novelty of the technique used or is there anything else?
We used a well tested technique which has been used in several studies of the gaseous properties of distant galaxies. What is new and exciting is the discovery of gas that does not contain "heavy" elements. This gas has been predicted by the Big Bang theory, but never observed before. We finally have an experimental confirmation of the theory that the most abundant elements in the universe (hydrogen and helium) were formed in the first minutes after the Big Bang.
The composition of the cloud, then, was inferred from the mark left in the light of the quasar. But how can we be sure that the characteristics you detected are not actually those of the original source?
When the particles of light (photons) travel in space between an object and us, they change color and become more red (the so-called redshift). By examining the spectrum, we can tell precisely which colors are associated with quasars and which are associated with gas. Therefore we know for sure that the gas is not in quasars. In addition, we know precisely the distance of the gas.
The current cosmological model suggests that in the first minutes after the Big Bang hydrogen, helium and a few other light elements were formed. Heavier ones - such as carbon, oxygen and silicon - would be synthesized by the first stars, at least two hundred million years later. Your survey has confirmed the presence of hydrogen and deuterium and the complete absence of heavier elements. What about helium?
Our experiment is not sensitive to helium. Therefore, although we are sure there is helium in the gas, we can not see it with the technique we are using. Still, it was really exciting to come across the first evidence of gas clouds having the same composition as that predicted by the Big Bang theory.
Two very old clouds then, and still untouched, probably the remains of those huge flows of cold gas from which the first galaxies in the Universe draw their nourishment. Cold flows which have only been theorized but never observed so far: who knows, may be the two clouds discovered by Fumagalli team are the tip of this long-awaited iceberg? | 0.829386 | 4.08495 |
Newswise — A new study published in the journal Nature shows how vigorous star formation can turn the tables on a starburst galaxy by forcing hydrogen and other gases high into the surrounding galactic halo, leaving little fuel for the next generation of stars.
These new observations may help solve the mystery of the missing high-mass galaxies that theories predict should exist, but are conspicuously absent.
Astronomers using the new Atacama Large Millimeter/submillimeter Array (ALMA) telescope have discovered billowing columns of cold, dense gas fleeing the disk of nearby starburst galaxy NGC 253, also known as the Silver Dollar Galaxy. Located 11.5 million light-years away in the constellation Sculptor, this galaxy -- with its slightly askew orientation -- offers astronomers an uncommonly clear view of several super star clusters near its center. These clusters denote areas where new stars are forming and they also mark the starting point for material being ejected from the galaxy.
"With ALMA's superb resolution and sensitivity, we can clearly see for the first time massive concentrations of cold molecular gas being jettisoned by expanding shells of intense pressure created by young stars. The amount of gas we measure gives us very good evidence that some growing galaxies spew out more gas than they take in," said Alberto Bolatto of the University of Maryland in College Park and lead author on the paper. "We may be seeing a present-day example of a very common occurrence in the early Universe."
These results may help explain why astronomers have found a surprising paucity of high-mass galaxies throughout the cosmos. Computer models show that many older galaxies should have considerably more heft and a larger stellar content than we currently observe. It's possible to account for this discrepancy by setting up some form of galactic winds or outflow of gas, which would deprive the galaxy of the fundamental material to form new stars.
One way to remove gas from a galaxy is to have gas falling in on a central supermassive black hole. As material swirls toward the black hole, it becomes superheated and produces powerful jets that can propel material far from the galactic disk and can even seed the intergalactic medium with heavy elements. But there is no indication that NGC 253's central black hole is currently active.
The other potential source of galactic winds is star formation, but until now this had not been observed with enough resolution or sensitivity to measure its impact on subsequent star formation or the outflow of gas.
As new stars form they exert powerful destructive influences on their environment. Initially, their light and winds of particles push on the surrounding gas. Later, if they are massive enough, stars explode as supernovas, a process that further drives the surrounding material away from the stellar birthplace. In NGC 253, the concentration of hundreds or thousands of such destructive stars in one place appears to have the effect of launching powerful flows of gas out of the galaxy.
"ALMA is opening a new window for observations of galactic winds," said Sylvain Veilleux, also at the University of Maryland and a coauthor on the paper. "Winds have the potential to be incredibly disruptive and carry away a significant fraction of the star-forming material of a galaxy."
Previous observations in the X-ray portion of the spectrum revealed hot ionized hydrogen streaming away from NGC 253's star-forming regions. This gas, however, is very tenuous and alone would have little if any impact on the fate of the galaxy and its ability to form future generations of stars.
The new ALMA data show the far-more-dense molecular gas getting its initial "kick" from the formation of new stars and then being swept along with the thin, hot gas on its way to the galactic halo. "These features trace an arc almost perfectly aligned with the edges of the previously observed hot, ionized gas outflow," noted Fabian Walter, a lead investigator at the Max-Planck Institute for Astronomy in Heidelberg, Germany, and a coauthor of the paper. "We can now see the step-by-step progression of starburst to outflow."
Using only a portion of its eventual full complement of 66 antennas, ALMA was able to measure the mass and motion of carbon monoxide (CO) in the gas ejected from the central regions of this galaxy. The researchers determined that vast quantities of molecular gas -- likely 9 times the mass of our Sun and possibly much more -- were being ejected from the galaxy each year. At this rate, the galaxy could run out of gas in as quickly as 60 million years. This would add up to be more gas than actually went into forming stars.
The researchers also determined that the gas is traveling anywhere between 40 to 250 kilometers per second, streaming approximately 1,500 light-years above and below the disk. This may not be fast enough for the gas to reach escape velocity from the galaxy. If not, the gas will likely get suspended in the galactic halo for many millions of years.
"More studies with the full ALMA array will help us figure out the ultimate fate of the gas carried away by the wind," said Adam Leroy with the National Radio Astronomy Observatory in Charlottesville, Virginia. "This will help us understand whether these starburst-driven winds recycle or truly remove star forming material."
"These spectacular results give an idea about the full power of ALMA when it will operate at its total capacity," adds ALMA Director Pierre Cox.
ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. | 0.845807 | 4.123509 |
Last year, a very unusual transient made headlines around the world as ‘the most luminous supernova ever discovered’. ASASSN-15lh was certainly incredibly bright — about double the previous record holder! However, it exhibited a number of weird properties that made it unlike any other superluminous supernova: a much higher temperature; a spectrum lacking most of the usual absorption lines; a huge rebrightening in the UV; and, perhaps most significantly, it occurred right in the centre of a massive, red galaxy that did not seem to be forming any stars. Hanging out at the centre of the galaxy is a clue that a supermassive black hole could be involved. I’ve been helping out some of my PESSTO collaborators with a new study led by Giorgos Leloudas (to be published in the first issue of Nature Astronomy) that shows that in fact most of the observed properties can be explained not as a supernova, but as a star that passed too close to the galaxy’s central black hole and got eaten alive — a so-called Tidal Disruption Event. It’s a messy meal, and the heat released as the stellar debris piles up into a viscous disk and then falls into the black hole can drive a luminous flare. In the case of ASASSN-15lh, it turns out the black hole also needs to be spinning rapidly. It will be fun to see if future data can definitively prove either the supernova or black hole interpretation of this amazing event! | 0.811185 | 3.613019 |
Materials from Heraeus have been used to explore the universe since the moon landing. They are helping find black holes, map the Milky Way, and even prove how the Earth really ‘ticks’.
The blue and white Delta II rocket thundered into the southern California sky in the morning hours of April 20, 2004. After the Delta II left the Earth’s atmosphere, it released a shimmering silver satellite into the stillness of outer space. Its name: Gravity Probe B. This satellite houses a marvel straight out of a science fiction blockbuster. Some of the world’s most talented physicists worked for decades on this invention to prove Einstein’s theory of relativity.
A bowling ball on a trampoline
The marvel consists of a gleaming block of Heraeus fused silica that is connected to a fused silica telescope and contains four gyroscopes. These spheres, also made of Heraeus fused silica, are the size of ping-pong balls and rotate up to 10,000 times per minute. At the time of the rocket launch, they were the most perfectly spherical objects ever made by human hands. The scientists controlling the satellite from Earth were inspired by Einstein’s theory that the Earth’s mass warps space-time – just like the weight of a bowling ball does a trampoline. The researchers hoped that this effect would alter the furious rotation of the small spheres on board the satellite. But would it prove true?
Twinkle, twinkle, little star
The satellite orbited the Earth for months, and the data that Gravity Probe B sent back to Earth actually did prove Einstein’s theory that the Earth warps space-time. So what happened to Gravity Probe B next? It was officially shut off on December 10, 2010, and has been orbiting the Earth ever since. You can see it up in the night sky, where it will continue to orbit the Earth for 30 years before burning up in the atmosphere.
Mapping the Milky Way
Heraeus technology is also used deep in outer space on the European satellite Gaia, 1.5 million kilometers from Earth. Gaia basically looks like a silver-colored top hat with a diameter of 10 meters. Its high-tech innards are working to fulfill the dreams of many astronomers by creating a three-dimensional map of the Milky Way. Creating such a map requires a highly sensitive camera, and several of its optical components, such as lenses and prisms, are made from Heraeus quartz glass. When the Gaia mission ends in July 2019, the finished 3D map – charting one billion stars, asteroids, and planets – will change how we see the night sky and deep space.
Tracking gravitational waves
Heraeus will play a role in the future of space exploration as well, in what is possibly the most ambitious ESA project yet: the LISA gravitational wave detector. Quickly orbiting or collapsing celestial bodies, such as stars or black holes, emit gravitational waves, which can slightly shift other masses. In 2018, a Nobel Prize was awarded for the discovery of this movement, which confirmed the existence of gravitational waves. The VIRGO and LIGO detectors, both of which are stationed here on Earth, are already using ultrapure Heraeus quartz glass.
Gold cubes in outer space
Three satellites carrying gold-platinum alloy cubes made by Heraeus will be positioned in deep space in 2034 to detect gravitational waves. A gravitational wave that encounters cubes like these will slightly change the cube’s shape and movement, enabling the detection of cosmic waves that ripple through the entire universe. This technology should make it easier to locate black holes. So, is this science fiction? No. An experiment has already shown that LISA’s measurements are five times more precise than expected. The future is already here.
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As we head into the 2018 Atlantic hurricane season, now is a good time to reflect on the accomplishments achieved by CYGNSS since its launch in December 2016. Early mission operations focused on engineering commissioning of the satellites and of the constellation as a whole. One achievement in particular is noteworthy. The satellites have no active means of propulsion, yet their relative spacing is important for achieving the required spatial and temporal sampling. The desired spacing is achieved by individually adjusting a spacecraft’s orientation and, as a result, the atmospheric drag it experiences. This technique is referred to as “differential drag”. An increase in drag will lower a satellite’s altitude, thereby changing its orbital velocity. We adjust the distance between spacecraft by adjusting their relative velocities. This is a new way of managing the spacing between a constellation of satellites, and one that can be significantly less risky and lower in cost than using traditional active propulsion. As a result, we were able to afford more satellites for the same price, which ultimately led to better, more frequent, sampling of short lived, extreme weather events like tropical cyclones.
Here is a figure, provided by CYGNSS team member Kyle Nave of ADS, illustrating the change in relative speed between two of the CYGNSS spacecraft that occurred the first time a differential drag maneuver was performed, on February 23, 2017.
The orbital phase rate between the two spacecraft is shown before, during and after the higher of the two had its orientation changed to maximize atmospheric drag. Phase rate measures how quickly the angle between two satellites changes. By increasing the drag on the higher one, it lowers to an altitude and orbital velocity closer to the lower one, thus reducing the phase rate. This was an important first confirmation of our ability to perform the maneuver. Since then, there have been many more drag maneuvers. Five of the eight satellites are now properly positioned relative to one another at a common altitude, and the remaining three are expected to have their drag maneuvers completed later this year.
The primary science objective of the CYGNSS mission is measurement of near surface wind speed over the ocean in and near the inner core of tropical cyclones. In an earlier NASA blog, (15 Dec 2017), I reported on our measurements of Hurricane Maria made in September 2017. Since that time, we have been examining the quality of our measurements both within and away from major storms. Measurements at ocean wind speeds below 20 m/s (44 mph) were found to have an RMS uncertainty of 1.4 m/s (3 mph). Measurements of storm force winds during the 2017 Atlantic hurricane season were found to have an uncertainty of 17% of the wind speed. The analysis that produced these results is reported in Ruf et al. (2018). DOI: 10.1109/JSTARS.2018.2825948.
CYGNSS operates continuously, over both ocean and land, and the land data have been another focus of recent investigations. The quality of some of those measurements, in particular regarding its spatial resolution, has come as something of a pleasant surprise. Here is one example of CYGNSS land imagery, of the Amazon River basin in South America, provided by Dr. Clara Chew of UCAR.
In the image, inland water bodies are prominently visible. This includes not only the major arms of the Amazon River but also its quite narrow minor tributaries. Careful examination of this and similar CYGNSS images suggests that the spatial resolution is markedly better here than it is over typical open ocean areas. The explanation lies in a transition of the electromagnetic scattering from an incoherent, rough surface regime over ocean to a largely coherent, near specular regime over inland waters. The fact that coherently scattered signals have inherently better spatial resolution is a well known phenomenon. What was unexpected is the widespread, global extent to which land surface conditions support coherent scattering. It requires the height of the surface roughness to be significantly below the wavelength of the radiowave signal, which in our case is 19 cm. This is apparently a ubiquitous property of wetland regions. It is a very fortuitous property for us, as it should enable an entirely new direction in scientific applications of CYGNSS measurements over land. NASA has recently added new investigators to the CYGNSS team specifically to study these new and exciting land applications.
A recent article summarizing these and other CYGNSS achievements, as well as some of the future applications of its measurements, is available at <www.nature.com/articles/s41598-018-27127-4>. The mission has demonstrated that smaller, more cost-efficient satellites are able to make important contributions to the advancement of science. In the months and years ahead, CYGNSS will hopefully be able to demonstrate that those advances can lead to practical scientific applications, such as extreme weather monitoring and prediction, that will benefit humankind. | 0.803636 | 3.077976 |
On Saturday evening, March 8, 2008, skywatchers across the southern United States might see a relatively bright star wink out briefly as one of
the two known moons of asteroid 45 Eugenia covers it. By observing this rare event, you could help determine the location of the moon relative to
the main asteroid more accurately than can be done directly even with the largest telescopes on (or near) Earth.
Eugenia itself will briefly hide the same star for skywatchers in a path across Mexico, whereas both moons will do so for parts of the southern
No matter which of these events you are positioned for, the time interval to be watching is 5:42 to 5:45 Universal Time on March 9th, which is
Saturday evening in North America. In local time, this is the three-minute interval that starts at 9:42 pm PST, 10:42 pm MST, and 11:42 pm CST.
WEATHER UPDATE (inserted early March 8th): The
Astro Meteo (30-hour prognosis) cloud-cover forecast maps show more clouds than before, especially in central California (including the central part
of the Central Valley) and over northern New Mexico. Southern
California looks good (including the southern San Joaquin Valley) but
there are clouds in the mountains and along I-10 in the desert. The
clouds in Texas may be thin enough to observe near Lubbock, but thin
clouds may extend all the way to Dallas; that may cause trouble, given
the event's 16° altitude there. I plan to observe in what should
be clear sky southeast of there, along US 259 and US 59. East of
Texas looks completely clear except possibly some thin clouds near
where Tom Campbell plans to observe.
It's worth pointing out that, back in 1977, astronomers laughed when Paul Maley and I suggested that asteroids
might have small moons based on visual observations of their occultations (eclipses) of stars. In 1994 they stopped laughing when images returned
from the Galileo spacecraft showed Dactyl, the small moon of asteroid 243 Ida. Nowadays, of course, many dozens of moons of asteroids are known.
But on only three occasions have confirmed timings been made when these moons covered stars (and those observations were all made in Japan).
A Three-in-One Bonanza
The star to be covered is easy to spot in binoculars. It lies about 5° east of Aldebaran and the Hyades V of stars in Taurus. At
visual magnitude 5.7, it is the brightest in a unique group of five stars. The target star
is ZC 741 (also designated SAO 94227 or HIP 23043) and is located at
right ascension 4h 57.4m,declination +17° 09' (equinox 2000.0).
The occultation by Eugenia itself, about 215 km in diameter, will last up to 12 seconds in its path crossing northern Mexico over Loreto
(in Baja California Sur), Torreon, Saltillo, and Monterrey.
The occultation by Eugenia's 13-km larger moon, Petit-Prince, will last about 0.7 second in a path across southern California (nominally
over King City and Tipton, but observers all the way from San Francisco to Los Angeles have almost an equal chance to see it), southern Nevada,
northern Arizona (Flagstaff area) and New Mexico, Texas (Lubbock and Dallas/Ft. Worth, but Waco to southern Oklahoma have a chance), northern
Louisiana, and southern Mississippi. This event might also be seen, low in the sky, from the Florida panhandle early Sunday morning, March 9th,
where the local time is 12:42 to 12:45 am EST.
The occultation by Eugenia's smaller moon, called Petite-Princesse, will be more difficult to observe. A mere 6 km or so across, it could
cover the star for roughly a third of a second in a narrow path through northern Mexico and southern Texas. The location of this path is
especially uncertain; it could go almost anywhere between San Antonio and Brownsville, Texas. (It might even go farther south, in Mexico; there's
some chance that those in the northern part of the occultation path for Eugenia could have an event by Petite-Princesse.)
Equipment and Techniques
Binoculars are fine for observing these eclipses by either Eugenia or its moons. Any telescope with an aperture of at least 2.4 inches (60 mm)
will also do. Much information about timing occultations of all types is in the International Occultation Timing Association's free
handbook, "Chasing the Shadow: The IOTA Occultation Observer's
Many imaging enthusiasts have CCD cameras on their scopes, and they may not want to remove them for this event. These people can also contribute
usefully. IOTA's David Herald invites them to look at this technique.
"If this event is well observed," Herald notes, "the profiles of the components will be resolved at the 1-km level, relative positions being
determined to within a few hundred microarcseconds. So I encourage everyone near the predicted paths to join in the group activity and
monitor this event! And remember, the uncertainty in the path location could be a good 100 km or more. So even if you are outside the predicted
paths, you should still monitor the event."
For More Information
On the IOTA website,
go to the box at the bottom of the page for finder charts and other useful links concerning this event.
Also, for making observations with whatever you have available, go here.
Simply reporting to us whether or not an eclipse of the star occurred or at your location can be important (especially if it does occur).
The interactive Google maps on Derek Breit's website (click on
"Spectacular Triple Asteroid Occultation — 45 Eugenia" near the top) also include static maps showing the ground paths, with green lines
showing the predicted central line, blue lines showing the northern and southern limits, red lines showing the standard error limits (1 sigma),
and gray lines showing less likely limits (2 sigma). Read the information in the boxes for the interactive maps if you use them; they can be used
to view the paths on detailed maps, satellite images, and in some cases aerial photography or other maps, to almost any desired level of detail.
Derek Breit's site also includes a list of stations and cities in and near the predicted path, ordered by distance in kilometers from the
predicted central line (distances north of the line are considered negative). For each it gives the predicted time of the center of the
occultation, the probability that an occultation will occur, and the local circumstances (mainly, in this case, the altitude above the western
horizon) of the event.
Notice that the event will occur at about 12° altitude above the horizon along I-35 between Dallas and Oklahoma City, so observers in that
area and farther east, where the altitude will be even lower, need to take care to find large open fields, the east sides of lakes, or otherwise
places with an unobstructed view of the western horizon.
Some Added Requests
Those in the possible region of visibility of these events are urged to publicize them as much as possible, via astronomical-society list servers,
science writers for public media, etc. And if you haven't already, please let us know where you plan to observe from. As soon as we have
information about fixed-site observers, we can direct mobile observers where to go so as to fill in any gaps in coverage.
coordinating plans for events involving the Eugenian satellites.
If you are reading an e-mailed copy of this AstroAlert, be sure to look at the online version at SkyandTelescope.com/AstroAlert for possible late updates.
Good luck with your observations!
Sky & Telescope | 0.852048 | 3.762413 |
In January 2006, astronomers focused the Hubble Space Telescope on an icy rock near the orbit of Uranus — and found twins. The object, known as 2002 CR46, turned out to be a binary: a minor planet the size of Rhode Island orbiting another the size of Connecticut at a distance of 1,300 kilometers (800 miles).
Many main-belt asteroids and Kuiper Belt objects (KBOs) are binary, but 2002 CR46 is the first known binary Centaur. Icy bodies in highly unstable orbits, Centaurs routinely cross paths with the giant planets, whose strong gravity should split apart any binaries. The Hubble team calculates that 2002 CR46 must have encountered Uranus and Neptune hundreds or thousands of times, yet somehow its two components stuck together.
“It’s been bumping around like a pinball for several million years,” says Keith Noll (Space Telescope Science Institute), who leads the ongoing Hubble survey. “But our calculations show that it’s not unreasonable that this thing could survive.” Apparently, its routine close encounters are not close enough.
The sticking power of 2002 CR46 hints at the existence of binary comets. Most short-period comets begin as KBOs, transition to Centaurs, then are kicked into the inner solar system by giant planets. And if binary Centaurs can survive multiple close encounters with these behemoths, they might also survive the final leap to become binary comets.
Many comets break into pieces due to interactions with giant planets or violent eruptions of vaporizing ice. But according to Brian Marsden (Minor Planet Center), astronomers know of no comet that was born a binary.
If a binary transitioned from a KBO to a comet, we would have to rethink how tightly bound these objects are,” says Hubble team member Denise Stephens (Johns Hopkins University).
In an upcoming paper in Icarus, Noll’s team will report on 2002 CR46 and a second binary Centaur — 2003 FX128 — bringing the total number of known double minor-planets to almost 100. No longer statistically unlikely anomalies, binaries now seem to be a natural outcome for all kinds of minor planets.
“We’re discovering that these objects are so abundant,” says Stephens. “Maybe it’s not as easy to break up binaries as we thought it would be.” | 0.85027 | 3.845549 |
There is a small chance that an asteroid the size of the Empire State Building could crash into Earth and cause destruction in 2135, but NASA is already working on a plan to prevent that from happening.
Stick with this for a second, but the plan in development includes astrophysicists and using nuclear weapons to deflect asteroid Bennu's trajectory away from Earth. NASA and the National Nuclear Security Administration have come up with two realistic responses in the event a near-Earth object approached Earth that includes using a spacecraft as either a kinetic impactor or to carry nuclear explosive weapons to deflect the object.
The Washington Post reports that the odds of Bennu hitting Earth in 2135 are currently about 1 in 2,700. For those looking for a comparison, Virginia Commonwealth University's run to the NCAA Tournament's Final Four in 2011 had about 5,000 to 1 odds.
"The next very close approach of Bennu to Earth is predicted to occur in 2135, when the asteroid is expected to pass just slightly within the moon's orbit," the U.S. space agency reports. "This particularly close approach will change Bennu's orbit by a small amount, which is uncertain at this time and which may lead to a potential impact on Earth sometime between 2175 and 2199.
"CNEOS (Center for Near Earth Object Studies)has calculated that the cumulative risk of impact by Bennu during this 24-year period is 0.037% or a 1 in 2,700 chance. That means there is a 99.963% probability that Bennu will not impact the Earth during this quarter-century period."
The space agency points out the general assumption that predicting something a century out comes with a level of uncertainty, but that its OSIRIS-REx mission would help researchers keep its orbit and trajectory updated.
NASA has been studying Bennu since it launched the OSIRIS-REx spacecraft in 2016. The space agency reports the spacecraft is expected to reach Bennu in December of this year, and return a sample of the asteroid to Earth by 2023.
As of Oct. 2, 2017, NASA reports the OSIRIS-REx spacecraft was more than 3 million miles from Earth or about 13 times the distance between our planet and its moon.
As for the space agency and nuclear administration's ideas -- presented in a study published in Science Direct --, they also point to the OSIRIS-REx mission as for why they picked Bennu for its study. Scientists from the Lawrence Livermore National Laboratory were apart of this national team, and went as far to design a 9-meter-tall, 8.8-ton spacecraft that would work as either the kinetic impactor or the nuke carrier.
Scientists dubbed the spacecraft HAMMER, which is short for Hypervelocity Asteroid Mitigation Mission for Emergency Response Vehicle, according to a news release from the lab. If the HAMMER were launched toward Bennu to deflect it, researchers believe it would take at least 7.4 years to do so which includes manufacturing, training, launching the conceptual spacecraft and much more.
"The preferred approach to mitigating an asteroid threat would be to deflect it by ramming a kinetic impactor into it, delivering a gentle nudge large enough and soon enough to slow it down and change its collision course with Earth, but not so large that the object breaks apart," the release reads. "This study helped quantify the threshold where a kinetic impactor would no longer be an effective deflection option."
The biggest question posed by the study is the option to act now or wait it out to see if that 1 percent probability rises or falls in the future. Co-author Kirsten Howley said in the release that the "probability of a Bennu impact may be 1 in 2,700 today, but that will almost certainly change - for better or worse - as we gather more data about its orbit." | 0.816884 | 3.036538 |
An image of how one element of the SKA might look. Image credit: Chris Fluke. Click to enlarge
European funding has now been agreed to start designing the world’s biggest telescope. The “Square Kilometre Array” (SKA) will be an international radio telescope with a collecting area of one million square metres – equivalent to about 200 football pitches – making SKA 200 times bigger than the University of Manchester’s Lovell Telescope at Jodrell Bank and so the largest radio telescope ever constructed. Such a telescope would be so sensitive that it could detect TV Broadcasts coming from the nearest stars.
The four-year Square Kilometre Array Design Study (SKADS) will bring together European and international astronomers to formulate and agree the most effective design. The final design will enable the SKA to probe the cosmos in unprecedented detail, answering fundamental questions about the Universe, such as “what is dark energy?” and “how did the structure we see in galaxies today actually form?”.
The new telescope will test Einstein’s General Theory of Relativity to the limit – and perhaps prove it wrong. It is certain to add to the long list of fundamental discoveries already made by radio astronomers including quasars, pulsars and the radiation left over from the Big Bang. By the end of this decade the design will be complete and astronomers anticipate building SKA in stages, leading to completion and full operation in 2020.
The SKA concept was first proposed to observe the characteristic radio emission from hydrogen gas. Measurements of the hydrogen signature will enable astronomers to locate and weigh a billion galaxies.
As the University of Manchester’s Prof Peter Wilkinson points out, “Hydrogen is the most abundant element in the universe, but its signal is weak and so a huge collecting area is needed to be able to study it at the vast distances that take us back in time towards the Big Bang”. To which Prof Steve Rawlings, University of Oxford, adds,”The distribution of these galaxies in space tells us how the universe has evolved since the Big Bang and hence about the nature of the Dark Energy which is now making the universe expand faster with time”.
Another target for the SKA is pulsars – spinning remnants of stellar explosions which are the most accurate clocks in the universe. A million times the mass of the Earth but only the size of a large city, pulsars can spin around hundreds of times per second. Already these amazing objects have enabled astronomers to confirm Einstein’s prediction of gravitational waves, but University of Manchester’s Dr Michael Kramer is looking further ahead. “With the SKA we will find a pulsar orbiting a black hole and, by watching how the clock rate varies, we can tell if Einstein had the last word on gravity or not”, he says.
Prof Richard Schilizzi, the International SKA Project Director, stresses the scale of the instrument needed to fulfil these science goals. “Designing and then building, such an enormous technologically-advanced instrument is beyond the scope of individual nations. Only by harnessing the ideas and resources of countries around the world is such a project possible”. Astronomers in Australia, South Africa, Canada, India, China and the USA are collaborating closely with colleagues in Europe to develop the required technology which will include sophisticated electronics and powerful computers that will play a far bigger role than in the present generation of radio telescopes. The European effort is based on phased array receivers, similar to those in aircraft radar systems. When placed at the focus of conventional mass-produced radio ‘dishes’, these arrays operate like wide-angle radio cameras enabling huge areas of sky to be observed simultaneously. A separate, much larger, phased array at the centre of the SKA will act like a radio fish-eye lens, constantly scanning the sky.
Funding for this global design programme has been provided by the European Commission’s Framework 6 ‘Design Studies’ programme, which is contributing about 27% of the total ?38M funding over the next four years. Individual countries are contributing the remainder. The UK has invested ?5.6M (?8.3M) funding provided by PPARC.
When coupled with the UK’s share of the EC contribution, then the UK’s overall contribution to the SKA Design Study (SKADS) programme is about 30% of the total.
The ?38M European technology development programme is funded by the European Commission and governments in eight countries led by the Netherlands, the UK, France and Italy. The programme is being coordinated by Ir. Arnold van Ardenne, Head of Emerging Technologies at The Netherlands ASTRON Institute. In van Ardenne’s view “the critical task is to demonstrate that large numbers of electronic arrays can be built cost effectively – so that our dreams of radio cameras and radio fish-eye lenses can be turned into reality”.
In the UK, a group of universities currently including Manchester, Oxford, Cambridge, Leeds and Glasgow, funded by PPARC, is involved in all aspects of the design but is concentrating on sophisticated digital phased arrays and the distribution and analysis of the enormous volumes of data which the SKA will produce. University of Cambridge’s Dr Paul Alexander makes the point that “the electronics in the SKA makes it very flexible and allows for completely new ways of scanning the sky. But to make it work will require massive computing power”. Designers believe that by the time the SKA reaches full operation, 14 years from now, a new generation of computers will be up to the task.
The geographical location of SKA will be decided in the mid-term future and several nations have already expressed interest in hosting this state of the art astronomical facility.
Original Source: PPARC News Release | 0.860345 | 3.893029 |
NASA begins testing Mars lander for next mission to red planet
Testing is underway on NASA's next mission on the journey to Mars, a stationary lander scheduled to launch in March 2016.
The lander is called InSight, an abbreviation for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. It is about the size of a car and will be the first mission devoted to understanding the interior structure of the Red Planet. Examining the planet's deep interior could reveal clues about how all rocky planets, including Earth, formed and evolved.
The current testing will help ensure InSight can operate in and survive deep space travel and the harsh conditions of the Martian surface. The spacecraft will lift off from Vandenberg Air Force Base in California, and land on Mars about six months later.
The technical capabilities and knowledge gained from Insight, and other Mars missions, are crucial to NASA's journey to Mars, which includes sending astronauts to the Red Planet in the 2030s.
"Today, our robotic scientific explorers are paving the way, making great progress on the journey to Mars," said Jim Green, director of NASA's Planetary Science Division at the agency's headquarters in Washington. "Together, humans and robotics will pioneer Mars and the solar system."
During the environmental testing phase at Lockheed Martin's Space Systems facility near Denver, the lander will be exposed to extreme temperatures, vacuum conditions of nearly zero air pressure simulating interplanetary space, and a battery of other tests over the next seven months. The first will be a thermal vacuum test in the spacecraft's "cruise" configuration, which will be used during its seven-month journey to Mars. In the cruise configuration, the lander is stowed inside an aeroshell capsule and the spacecraft's cruise stage - for power, communications, course corrections and other functions on the way to Mars—is fastened to the capsule.
"The assembly of InSight went very well and now it's time to see how it performs," said Stu Spath, InSight program manager at Lockheed Martin Space Systems, Denver. "The environmental testing regimen is designed to wring out any issues with the spacecraft so we can resolve them while it's here on Earth. This phase takes nearly as long as assembly, but we want to make sure we deliver a vehicle to NASA that will perform as expected in extreme environments."
Other tests include vibrations simulating launch and checking for electronic interference between different parts of the spacecraft. The testing phase concludes with a second thermal vacuum test in which the spacecraft is exposed to the temperatures and atmospheric pressures it will experience as it operates on the Martian surface.
The mission's science team includes U.S. and international co-investigators from universities, industry and government agencies.
"It's great to see the spacecraft put together in its launch configuration," said InSight Project Manager Tom Hoffman at NASA's Jet Propulsion Laboratory, Pasadena, California. "Many teams from across the globe have worked long hours to get their elements of the system delivered for these tests. There still remains much work to do before we are ready for launch, but it is fantastic to get to this critical milestone." | 0.8052 | 3.063075 |
An exoplanet smaller than Neptune with its own atmosphere has been discovered in the Neptunian Desert around its star by an international collaboration of astronomers, with the University of Warwick taking a leading role.
Technically known as NGTS-4b, also nick-named ‘The Forbidden Planet’ by researchers, is three times the size of Earth and twenty percent smaller than Neptune. It is hotter than Mercury with a temperature of 1,832 degrees Fahrenheit. The planet has its own atmosphere. It orbits around the star in only 1.3 days which is equivalent of Earth’s orbit around the sun of one year.
It is the first exoplanet of its kind to have been found in the Neptunian Desert.
An international team of astronomers Dr. Richard West including Professor Peter Wheatley, Dr. Daniel Bayliss and Dr. James McCormac from the Astronomy and Astrophysics Group at the University of Warwick, has identified a rogue planet.
The astronomers said that the Neptunian Desert is the region close to stars where no Neptune-sized planets are found. Planets in this area do not retain their gaseous atmosphere and evaporate leaving just a rocky core because of the strong irradiation from the star.
Astronomers believe that either the planet moved into this region within the last million years, or the planet itself was once bigger and the atmosphere is in the process of evaporating evaporating.
This has sparked a new search for more planets and missions like NASA’s planet-hunter TESS could further explore the region. | 0.809232 | 3.178218 |
The universe is vast. It’s hard to comprehend just how big it is. For me, this image helps make that visceral. Without any effort, more than a dozen galaxies are visible and, with careful inspection dozens, perhaps close to a hundred are visible in the frame.
These galaxies are part of the Virgo Cluster, a large group of galaxies. You may have recently heard the name of the larger, fuzzy galaxy at the top of the image, M87. It was in the news in April 2019 because the region around the supermassive black hole at its center was imaged for the first time. To put this image in perspective, that black hole image would occupy roughly 1/100,000 of a pixel in my image.
The arc of galaxies across the bottom is called Markarian’s Chain. It is named after an astronomer who was the first to realize they were gravitationally bound together. However, although M87 and Markarian’s Chain are the stars of this image (pun slightly intended), they have a large supporting cast. The image below shows just how many galaxies are really there.
Each of those circles represents a galaxy. On the full size image most of those circles actually contain a small, fuzzy blog. It’s a big universe!
This image included a lot of firsts for me. It was the first image taken with a mono camera and filters. It was the first to use an electronic focuser and rotator. It was the first time I combined data taken over two nights. However, it was not without its challenges. Though it is over two nights, it’s only 2.6 hours of data. Technical glitches limited the first night to an hour of data and the second night to 1.6 hours. On the third night, thanks to the help of a kind soul on the cloudy nights Internet forum I was able to make some major progress on one of my technical issues and collect more than two additional hours of data Even so, at only 4.8 hours there is a lot going on in the frame. These galaxies are on the order of 50-55 million light years away and many of the galaxies are elliptical. Ellipticals never have the kind of detail that spiral galaxies do and the distance hides what there is, but on the spirals in the frame a hint of structure is visible.
After looking at this for a while I became curious if the image contained any quasars. Back when they were first discovered it wasn’t known what a quasar was except that it was very distant and incredibly energetic. We’ve since learned that a quasar is an extremely energetic luminous galactic nucleus. The quasar can put out as much light as the rest of the galaxy combined. On my image they wouldn’t be more than dots but even imaging one would be pretty amazing. The software I used for the annotation above didn’t have a catalog containing quasars but I found and massaged a copy of the half million quasar catalog and made a new annotated image combining the quasar catalog with the galaxy catalog shown above. I wasn’t sure what to expect. I figured there might be a few candidates in the frame but, much as with the galaxy annotation above I was surprised to see this:
The white annotations are where a quasar is known to exist. At first I was disappointed. I wasn’t seeing anything in the crosshairs of all those white annotations. But, eventually I found one and by the time I was done I found eight (possibly nine) that seem likely to be quasars:
|Catalog Number||Redshift (z)||Age (billions of years)|
|SDSS J123232.20+124548.9||1.145||8.449||might actually be a foreground object as it is off center in the cross hair|
The redshift value is a measure of how much the light has been shifted toward the red part of the spectrum. The larger this value, the further away the object is from us. The age value is a measure of how many billions of years ago the light began it’s journey to us. The catalog I used provided the redshift value (known as ‘z’) but the age values come from this website. It has a calculator where you enter ‘z’ and it provides a lot of information I’m not entirely sure how to interpret yet. My goal was to find the distance but the most relevant information I found was age of the universe at that redshift value. If I’m understanding it properly then age should be the distance of the object in light years at the start of its journey but I could be misinterpreting that.
If I’m interpreting this correctly and if I’ve used the catalog correctly then the most distant object on the image is 10.885 billion light years away (or was when that light started toward us). The actual spot on the image is barely a smudge brighter than the background. It’s not at all visually impressive but It amazes me that a small, 80mm refractor can capture light that is far older than our own sun’s age. More than twice as old.
Of course, I could have made a mistake somewhere along the line so I’m not certain of anything but so far I think I’ve got things right.
For comparison, the subject galaxies in Markarian’s Chain and M87 are in the range of 50 to 60 million light years distant. While that is incredibly far away it is a tiny fraction of the distance to those quasars, even the closest of them. I haven’t checked all the PGC galaxies but I’ve spot decked a few and they seem to range out to around two billion light years or so.
Spring is called “galaxy season” because the night sky is looking out of our galaxy making it the best time of year to observe the things outside the Milky Way compared to the rest of the year when our night sky is looking into our galaxy. However, for a small telescope like I am using, it is a challenging time of year because these are small in the frame. Fortunately, there are areas of the sky like this where the structure of the universe can be observed allowing us to see exactly how small a part of the universe we sit in. | 0.818799 | 3.684571 |
Seeing Stars - Inverness Courier, Friday7th Dec, 2007
The Clouds Of Orion
By Antony McEwan - Highlands Astronomical Society
During the cold dark nights of December the southern sky is home to one of the largest and most recognisable constellations in the night sky: Orion. The hourglass-shaped asterism that marks out the Hunter’s body contains stars that are all brighter than third magnitude and stand out very well against a dark sky background.
Famous for the Great Orion Nebula (Messier 42) situated in the part of the constellation known as “Orion’s Sword”, Orion is home to many other visual wonders (many of which are easily seen with a small telescope) including emission nebulae, reflection nebulae, dark nebulae, open clusters and binary star systems.
The Great Orion Nebula is only the most easily visible portion of the huge cloud of interstellar gas and dust that encompasses much of the constellation. The Great Orion Cloud, as it is known, is about 1500 light-years away from us and spans several hundred light-years. It is the interaction between parts of the cloud and stars near or within it that provide us with such beautiful deep sky objects to observe as astronomers.
It is fortuitous that such a visually rewarding constellation should appear at its best in the winter months, around the time that many potential new stargazers may find themselves in possession of brand new telescopes near the end of the month! Faced with the question, “What should I look at first?” a very good answer would be, “Orion!”
So where to start?
The trio of stars that make up Orion’s Belt are easy to find, and using moderate magnification on the star furthest to the right (Mintaka) will show its multiple nature. Although to the unaided eye the ‘star’ appears simply as a single point of light, in fact it has an easily detected companion star that orbits at a distance of about a quarter of a light-year. There is also a much fainter 14th magnitude companion between those two, and the brightest component star is in itself double, though this companion is much too close to be detected visually.
Moving the telescope to the star at the other end of the belt, Alnitak, puts you in position to see an emission nebula. This particular one is known as NGC 2024, or more romantically, the Flame Nebula. It is right beside Alnitak, so it is necessary to position the star just outside the field of view of the telescope so that its glare doesn’t overwhelm the view of the nebula. Skies permitting, you should see a faint u-shaped patch of nebulosity that will appear like wreaths of smoke against the sky. The ‘Flame’ shows its real beauty in long-exposure photographs, but if you do manage to see it visually relish the view – you’ve made a good start!
An emission nebula is basically a glowing cloud of interstellar gas. Radiation from nearby stars ionises the hydrogen-rich gas, stripping it of its electrons. The loose electrons gain energy from the ultraviolet radiation emitted from the nearby stars, and when they recombine with other atoms some of that energy is released in the visual wavelengths: light. So emission nebulae are glowing from within, powered by the stars at their hearts.
Reflection nebulae are slightly different. In these, the dust within the nebula is reflecting the light of nearby stars and scattering it, causing the nebulous material to glow. A terrestrial analogy would be, for example, watching the headlights of a car approaching in thick fog. A good example of a reflection nebula is Messier 78, situated about 2.5 degrees (a distance of about five full moon widths) to the north of Alnitak and slightly to the east (that is, to the left as we see it). Once found, it appears as a small fan-like smudge of ethereal light, with two 10th magnitude stars peering out through the gloom. The nebula is lit up not only by the light of these two stars, but by others associated with that part of the cloud as well.
Of course no night of observing Orion would be complete without treating yourself to a view of M42, the Great Orion Nebula itself. It is a place where the processes of star-creation have recently (in astronomical terms) taken place and are still occurring. The vast area of the nebula is alight with the glow from the hot, massive young stars that are newly formed, making it one of the most easily seen emission nebulae of the northern hemisphere. The haze is just about detectable by the unaided eye, but through a telescope the view is astounding. At the heart of the nebula can be seen the small group of stars that are ionising the cloud. Four can be seen easily in a small telescope, though there are more to be seen if larger apertures are used or the sky is particularly stable. Glowing fans of nebulosity spread out from this group of stars, known as the Trapezium, and arc back towards each other. Within the cloud can be seen variations in the density of the nebulosity and subtle shading – it is an unforgettable sight.
These are only some of the wonders contained within the borders of Orion, but they are some of the best examples of their types in the sky. What could be better – a dark December night, a new telescope to try out, and the full splendour of mighty Orion looming overhead in the Highland sky? Wrap up warm and enjoy the experience. | 0.828441 | 3.729698 |
How can we measure the masses of free-floating planets wandering around our galaxy? A new study identifies one approach that combines the power of two upcoming missions.
Finding Invisible Planets
Most exoplanets we’ve found so far have relied on measurements of their host stars, either via dips in the host star’s light as the planet passes in front (transit detections), or via wiggling of lines in the host star’s spectra caused by the planet’s gravitational tug (radial velocity detections). But free-floating planets have no hosts and are therefore effectively invisible, since they don’t give off much light of their own. To find these rogues, we rely on another method: gravitational microlensing.
In microlensing, the mass of a passing foreground planet — either free-floating or bound to a host star — can act as a lens, briefly gravitationally focusing the light of a background star behind it. As a result, the background star temporarily brightens (on timescales of perhaps seconds to years) in our observations. Though we never directly see the foreground planet, we can infer its presence from the spike in the background star’s brightness.
Masses from Parallax
By itself, a microlensing observation usually can’t tell us about the mass of a free-floating planet; this is because the timescale of a brightening event depends on both the mass of the lens and on the relative proper motion between the background source and the foreground lensing planet.
But if we could simultaneously observe a microlensing event from two different locations, separated by a large enough distance? Then the parallax would allow us to break that degeneracy: the differences in peak brightness and its timing at the two locations would allow us to calculate both the speed of lens relative to the source and the planet mass.
Vantage Points in Space
Where do we find two sensitive eyes located far enough apart to make this work? In space, of course!
NASA’s Wide Field Infrared Survey Telescope (WFIRST) is set for launch in the mid-2020s, and one of its primary mission objectives is to perform wide-field imaging that may allow for the detection of hundreds of free-floating planets — and many additional bound planets — via microlensing.
As for the second eye, scientists Etienne Bachelet (Las Cumbres Observatory) and Matthew Penny (The Ohio State University) propose that ESA’s upcoming Euclid mission is exactly what we need. Euclid, launching in 2022, will have similar wide-field imaging capabilities to WFIRST, and it will be able to make complementary microlensing parallax measurements as long as the two satellites are 100,000 km or more apart.
Making Use of Gaps
Though Euclid’s primary science goal is to study dark energy and dark matter, Bachelet and Penny demonstrate that a modest investment of Euclid observing time — approximately 60 days during its primary mission, and another 60 days during its extended mission — during scheduling gaps would be enough to obtain the masses for 20 free-floating planets and many more bound planets.
So what are we waiting for? Let’s go learn more about the rogue planets sneaking through our galaxy!
“WFIRST and EUCLID: Enabling the Microlensing Parallax Measurement from Space,” Etienne Bachelet and Matthew Penny 2019 ApJL 880 L32. doi:10.3847/2041-8213/ab2da5
This post originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society. | 0.821824 | 4.050716 |
Although the Cassini mission ended in September 2017, the data collected is still being examined by scientists. So much had been transmitted by the probe that it will take decades to sift through it all.
Recently, a science team led by Nozair Khawaja of the Free University of Berlin, were studying some of this data collected by the spacecraft’s Cosmic Dust Analyzer (CDA), which detected ice grains emitted from Enceladus into Saturn’s E Ring.
The scientists used the CDA’s mass spectrometer measurements to determine the composition of the material in the grains.
Powerful hydrothermal vents regularly eject material from the core of Enceladus. This material mixes with water from the moon’s massive subsurface ocean and then is released into space as water vapor and ice grains.
The team discovered new molecules condensed into the ice grains that turned out to be nitrogen and oxygen bearing compounds. These compounds were determined to be organic, the ingredients of amino acids.
Here on Earth, similar compounds are part of a chemical reactions that also produce these building blocks of life. Hydrothermal vents on our ocean floor provide the heat and energy that fuels these reactions. This lends to the belief that the hydrothermal vents on Enceladus might operate in the same way, by supplying the energy needed to produce amino acids.
And now, these organic compounds have been verified in the plumes of Enceladus.
“If the conditions are right, these molecules coming from the deep ocean of Enceladus could be on the same reaction pathway as we see here on Earth. We don’t yet know if amino acids are needed for life beyond Earth but finding the molecules that form amino acids is an important piece of the puzzle,” said Khawaja, whose findings were published October 2nd in the Monthly Notices of the Royal Astronomical Society.
These new findings work to complement the discovery made by the team last year of large, insoluble complex organic molecules that are believed to float on the surface of Enceladus’ ocean. These finding are what prompted the team to dive deeper with this recent work. Their goal was to hopefully find the ingredients, dissolved in the ocean, that would be needed to form amino acid formation.
“Here we are finding smaller and soluble organic building blocks – potential precursors for amino acids and other ingredients required for life on Earth,” said co-author Jon Hillier.
“This work shows that Enceladus’ ocean has reactive building blocks in abundance, and it’s another green light in the investigation of the habitability of Enceladus,” added co-author Frank Postberg.
Cassini-Huygens is a mission cooperative project of NASA, the European Space Agency (ESA), and the Italian Space Agency. NASA’s Jet Propulsion Laboratory (JPL) manages the mission for NASA’s Science Mission Directorate, Washington. To learn more about the mission and the science learned from its data, visit the official website. | 0.814558 | 3.961221 |
16 Cygni Bb
16 Cygni Bb or HD 186427 b is an extrasolar planet approximately 69 light-years away in the constellation of Cygnus. The planet was discovered orbiting the Sun-like star 16 Cygni B, one of two solar-mass (M☉) components of the triple star system 16 Cygni. It orbits its star once every 799 days and was the first eccentric Jupiter and planet in a double star system to be discovered.
|Discovered by||William D. Cochran, Artie P. Hatzes, R. Paul Butler, Geoff Marcy|
|Discovery site||United States|
|Discovery date||22 October 1996|
|1.681 ± 0.097 AU (251,500,000 ± 14,500,000 km)|
|Eccentricity||0.689 ± 0.011|
|798.5 ± 1.0 d|
|Inclination||45 or 135|
|2,446,549.1 ± 6.6|
|83.4 ± 2.1|
|Semi-amplitude||50.5 ± 1.6|
|Mass||2.38 ± 0.04 MJ|
In October 1996 the discovery of a planetary-mass companion to the star 16 Cygni B was announced, with a mass at least 1.68 times that of Jupiter (MJ). At the time, it had the highest orbital eccentricity of any known extrasolar planet. The discovery was made by measuring the star's radial velocity.
Unlike the planets in the Solar System, the planet's orbit is highly elliptical, and its distance varies from 0.54 AU at periastron to 2.8 AU at apastron. This high eccentricity may have been caused by tidal interactions in the binary star system, and the planet's orbit may vary chaotically between low and high-eccentricity states over a period of tens of millions of years.
Preliminary astrometric measurements in 2001 suggested the orbit of 16 Cygni Bb may be highly inclined with respect to our line of sight (at around 173°). This would mean the object's mass may be around 14 MJ; the dividing line between planets and brown dwarfs is at 13 MJ. However these measurements were later proved useful only for upper limits.
Because the planet has only been detected indirectly by measurements of its parent star, properties such as its radius, composition and temperature are unknown. A mathematical study in 2012 showed that a mass of about 2.4 MJ would be most stable in this system. This would make the body a true planet.
The planet's highly eccentric orbit means the planet would experience extreme seasonal effects. Despite this, simulations suggest that an Earth-like moon, should it have formed in an orbit so close to the parent star, would be able to support liquid water at its surface for part of the year.
- Plávalová, Eva; Solovaya, Nina A. (2013). "Analysis of the motion of an extrasolar planet in a binary system". The Astronomical Journal. 146 (5): 108. arXiv:1212.3843. Bibcode:2013AJ....146..108P. doi:10.1088/0004-6256/146/5/108.
- Cochran, William D.; et al. (1997). "The Discovery of a Planetary Companion to 16 Cygni B". The Astrophysical Journal. 483 (1): 457–463. arXiv:astro-ph/9611230. Bibcode:1997ApJ...483..457C. doi:10.1086/304245.
- Butler, R. P.; Marcy, G. W. (1997). "The Lick Observatory Planet Search". IAU Colloq. 161: Astronomical and Biochemical Origins and the Search for Life in the Universe: 331. Bibcode:1997abos.conf..331B.
- Butler, R. P.; et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal. 646 (1): 505–522. arXiv:astro-ph/0607493. Bibcode:2006ApJ...646..505B. doi:10.1086/504701.
- Holman, M.; Touma, J.; Tremaine, S. (1997). "Chaotic variations in the eccentricity of the planet orbiting 16 Cygni B". Nature. 386 (6622): 254–256. Bibcode:1997Natur.386..254H. doi:10.1038/386254a0.
- Han, I.; Black, D. C.; Gatewood, G. (2001). "Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions". The Astrophysical Journal Letters. 548 (1): L57–L60. Bibcode:2001ApJ...548L..57H. doi:10.1086/318927.
- Pourbaix, D.; Arenou, F. (2001). "Screening the Hipparcos-based astrometric orbits of sub-stellar objects". Astronomy and Astrophysics. 372 (3): 935–944. arXiv:astro-ph/0104412. Bibcode:2001A&A...372..935P. doi:10.1051/0004-6361:20010597.
- Williams, D. M.; Pollard, D. (2002). "Earth-like worlds on eccentric orbits: excursions beyond the habitable zone". International Journal of Astrobiology. 1 (1): 61–69. Bibcode:2002IJAsB...1...61W. doi:10.1017/S1473550402001064.
- Jean Schneider (2011). "Notes for Planet 16 Cyg B b". Extrasolar Planets Encyclopaedia. Retrieved 30 September 2011.
- "16 Cygni 2?". SolStation. Retrieved 2008-06-24.
- "16 Cygni-B". University of Illinois at Urbana–Champaign. The Planet Project. Archived from the original on 2008-05-18. Retrieved 2008-06-24.
- "16 Cyg B". Exoplanets. Archived from the original on 2009-11-25. Retrieved 2009-05-03. | 0.919478 | 3.972692 |
Guillaume Le Gentil
Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière (born Coutances, 12 September 1725 – died Paris, 22 October 1792) was a French astronomer who discovered several nebulae and was appointed to the Royal Academy of Sciences. He made unsuccessful attempts to observe the 1761 and 1769 transits of Venus from India.
Guillaume Le Gentil
|Died||22 October 1792 (aged 67)|
Guillaume Le Gentil was born in Coutances and first intended to enter the church before turning to astronomy. He discovered what are now known as the Messier objects M32, M36 and M38, as well as the nebulosity in M8, and he was the first to catalogue the dark nebula sometimes known as Le Gentil 3 (in the constellation Cygnus).
He was part of the international collaborative project organized by Mikhail Lomonosov to measure the distance to the Sun, by observing the transit of Venus at different points on the earth. Edmond Halley had suggested the idea, but it required careful measurements from different places on earth, and the project was launched with more than a hundred observers dispatched to different parts of the globe, for observing the transit coming up in 1761. A part of the French expedition, Le Gentil set out for Pondicherry, a French possession in India. He set out from Paris in March 1760, and reached Isle de France (now Mauritius) in July. However, the Seven Years' War had broken out between France and Britain in the meantime, hindering further passage east. He finally managed to gain passage on a frigate that was bound for India's Coromandel Coast, and he sailed in March 1761 with the intention of observing the transit from Pondicherry. Even though the transit was only a few months away, on 6 June, he was assured that they would make it in time. The ship was blown off-course by unfavorable winds and spent five weeks at sea. By the time it finally got close to Pondicherry, the captain learned that the British had occupied the city, so the frigate was obliged to return to Isle de France. When 6 June came the sky was clear, but the ship was still at sea, and he could not take astronomical observations with the vessel rolling about. Having already completed the trip from Paris, he stayed for the next transit of Venus, which would come in another eight years (they occur in pairs 8 years apart, but each such pair is separated from the next by 121 or 105 years).
After spending some time mapping the eastern coast of Madagascar, he decided to record the 1769 transit from Manila in the Philippines. Encountering hostility from the Spanish authorities there, he headed back to Pondicherry, which had been restored to France by peace treaty in 1763, where he arrived in March 1768. He built a small observatory to view the transit. On the day of the event, 4 June 1769, the sky became overcast, and Le Gentil saw nothing.
The return trip was first delayed by dysentery, and further when his ship was caught in a storm and dropped him off at Île Bourbon (Réunion), where he had to wait until a Spanish ship took him home. He finally arrived in Paris in October 1771, having been away for eleven years, only to find that he had been declared legally dead and been replaced in the Royal Academy of Sciences. His wife had remarried, and all his relatives had "enthusiastically plundered his estate". Due to shipwrecks and wartime attacks on ships, none of the letters he had sent to the Academy or to his relatives had reached their destinations. Lengthy litigation and the intervention of the king were ultimately required before he recovered his seat in the academy and remarried. He then lived for another 21 years.
During the time he spent in India, Le Gentil examined local astronomical traditions and wrote several notes on the topic. He reported that the duration of the lunar eclipse of 30 August 1765 was predicted by a Tamil astronomer, based on the computation of the size and extent of the earth-shadow (going back to Aryabhata, 5th century), and was found short by 41 seconds, whereas the charts of Tobias Mayer were long by 68 seconds.
Play and operaEdit
Le Gentil is the subject of a play by Canadian playwright Maureen Hunter. Transit of Venus was first produced at the Manitoba Theatre Centre in 1992. It was subsequently made into an opera of the same name with music by Victor Davies, presented by Manitoba Opera in 2007, and Opera Carolina in 2010.
- A detailed account of Le Gentil's expedition was published in a series of four articles by Helen Sawyer Hogg
- Le Gentil's own account was published in Voyage dans les mers de l'Inde, fait par ordre du Roi, à l'occasion du passage de Vénus, sur le disque du Soleil, le 6 juin 1761 & le 3 du même mois 1769 par M. Le Gentil, de l'académie royale des sciences. Imprimé par ordre de sa Majesté, two volumes, Paris 1779 and 1781.
- Works by or about Guillaume Le Gentil in libraries (WorldCat catalog)
- Timothy Ferris (1988). Coming of Age in the Milky Way. Anchor Books, Doubleday. p. 133. ISBN 978-0385263269.
- Wright, Michael (2012-02-07). "The Ordeal of Guillaume Le Gentil". Sidereal Times. University of Princeton. Retrieved 14 June 2012.
- Loader, Brian (2004). "The Periodicity of the Transits of Venus". Southern Stars. 43: 18. ISSN 0049-1640.
- Bill Bryson (2012) . A Short History of Nearly Everything. Doubleday Canada. p. 22. ISBN 978-0385674508.
- Voyage dans les mers de l'Inde, fait par ordre du Roi, à l'occasion du passage de Vénus, sur le disque du Soleil, le 6 juin 1761 & le 3 du même mois 1769 par M. Le Gentil, de l'Académie royale des sciences. Imprimé par ordre de sa Majesté, À Paris, de l'Imprimerie royale 1779 et 1781. 2 volumes in-4°. Via – Google-Livre
- Gentil, Le, G (1784). Remarques et observations sur l'Astronomie des Indiens, et sur l'ancienneté de cette Astronomie. Histoire de l’Académie royale des sciences. pp. 482–501.
- Danino, Michel (2016). "Le Gentil à Pondichéry : de Vénus à l'Inde" (PDF). Synergies Inde. 7: 29–43.
- Ansari, S. M. R. (March 1977). "Aryabhata I, His Life and His Contributions". Bulletin of the Astronomical Society of India. 5 (1): 10–18. Bibcode:1977BASI....5...10A. hdl:2248/502.
- Sawyer Hogg, Helen (1951). "Out of Old Books (Le Gentil and the Transits of Venus, 1761 and 1769)". Journal of the Royal Astronomical Society of Canada. 45: 37. Bibcode:1951JRASC..45...37S.
- Sawyer Hogg, Helen (1951). "Out of Old Books (Le Gentil and the Transits of Venus, 1761 and 1769 continued)". Journal of the Royal Astronomical Society of Canada. 45: 89. Bibcode:1951JRASC..45...89S.
- Sawyer Hogg, Helen (1951). "Out of Old Books (Le Gentil and the Transits of Venus, 1761 and 1769 continued, with Plate V)". Journal of the Royal Astronomical Society of Canada. 45: 127. Bibcode:1951JRASC..45..127S.
- Sawyer Hogg, Helen (1951). "Out of Old Books (Le Gentil and the Transits of Venus, 1761 and 1769 concluded)". Journal of the Royal Astronomical Society of Canada. 45: 173. Bibcode:1951JRASC..45..173S. | 0.870389 | 3.591611 |
Shine is back after a break over the summer! We are now in full preparation for our big science, music and art festival in the Byre Theatre on 7 November, and in the upcoming weeks we will use this blog to show you some of the activities that we have in mind.
The 2.5-meter Sloan Telescope at Apache Point Observatory. Credit: A. Weijmans
Today, let’s talk about observing galaxies. Our very own Dr. Anne-Marie Weijmans is the lead observer for MaNGA, which has nothing to do with Japanese cartoons, but everything with obtaining as much information as we can about nearby galaxies. MaNGA stands for Mapping Nearby Galaxies at Apache Point Observatory, which is a telescope site in New Mexico, US. APO is home of the 2.5-meter Sloan Telescope, and although this is a modest size for a telescope (the big ones in Hawaii and Chili have mirrors up to 8 meter in diameter!), the Sloan Digital Sky Survey is one of the most successful surveys in astronomy.
The Sloan Telescope first took images of a very large part of the northern sky, and then was equipped with a spectrograph, to unravel the light of galaxies in different wavelengths. This allowed astronomers to determine the composition and velocities of stars and gas in galaxies, learning more about the way that these galaxies formed. Now, the Sloan Digital Sky Survey measures properties of stars in the Milky Way (APOGEE survey), determines the cosmic expansion rate by measuring very accurate positions of far away galaxies (eBOSS survey), and maps nearby galaxies with MaNGA. How do they do that?
MaNGA lead observer Anne-Marie Weijmans in action, plugging a plate at Apache Point Observatory during the commission run. Credit: N. Drory
The answer is by using a very sophisticated and effective observing strategy, using plates. These plates are drilled in Seattle, using a very precise process. We start with an aluminum plate, and at each galaxy or star position, a hole is drilled. The plates are then shipped to APO, where a team of plate pluggers plugs one fiber into each hole. Each fiber goes to the spectrograph, so that when the observers during the night attach the plate to the telescope, the astronomers get a spectrum for each galaxy or star.
MaNGA test-run plate 6612 for observing at Apache Point Observatory, and now in Anne-Marie’s office. The colourful markings are indications for the pluggers, on how fibers should be grouped together during plugging. This plate will be on display in the Murray Studios in Anstruther, on Sunday 6 September during Fife Doors Open, 14:00 – 17:00. Credit: A. Weijmans
The Sloan Digital Sky Survey has some great movies on YouTube, that show you the drilling process, plugging, and night observing (click on the links to see the movies). And at Shine we are very lucky to have one of these plates in our possession: we have a very rare MaNGA plate, that was drilled for a test-run in January 2013, when MaNGA was still in its development phase. Anne-Marie spent 3 weeks at the APO mountain top that winter, to get all the test data in place.
Want to see this plate, and talk to Anne-Marie about her experience with observing galaxies with MaNGA? Then come this Sunday 6 September to Anstruther, where artist Tim Fitzpatrick has opened the doors of his studio for Fife Doors Open. Our MaNGA plate will be on display, and astronomer Kirstin Hay will also be there with a cosmic floor keyboard, where you can step along the expanding Universe. We’re at Murray Studios, 21 Cunzie Street, between 14:00 and 17:00. | 0.838717 | 3.613055 |
Extremely distant galaxies are usually too faint to be seen, even by the largest telescopes. But nature has a solution: gravitational lensing, predicted by Albert Einstein and observed many times by astronomers. Now, an international team of astronomers, led by Harald Ebeling of the Institute for Astronomy at the University of Hawaii at Manoa, has discovered one of the most extreme instances of magnification by gravitational lensing.
Using the Hubble Space Telescope to survey a sample of huge clusters of galaxies, the team found a distant galaxy, eMACSJ1341-QG-1, that is magnified 30 times thanks to the distortion of space-time created by the massive galaxy cluster dubbed eMACSJ1341.9-2441.
The underlying physical effect of gravitational lensing was first confirmed during the solar eclipse of 1919, and can dramatically magnify images of distant celestial sources if a sufficiently massive object lies between the background source and observers.
Galaxy clusters, enormous concentrations of dark matter and hot gas surrounding hundreds or thousands of individual galaxies, all bound by the force of gravity, are valued by astronomers as powerful "gravitational lenses." By magnifying the galaxies situated behind them, massive clusters act as natural telescopes that allow scientists to study faint and distant sources that would otherwise be beyond the reach of even the most powerful man-made telescopes.
"The very high magnification of this image provides us with a rare opportunity to investigate the stellar populations of this distant object and, ultimately, to reconstruct its undistorted shape and properties," said team member Johan Richard of the University of Lyon, who performed the lensing calculations.
Although similarly extreme magnifications have been observed before, the discovery sets a record for the magnification of a rare "quiescent" background galaxy--one that, unlike our Milky Way, does not form new stars in giant clouds of cool gas.
Explained UH team leader Ebeling, "We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing. This discovery stands out, though, as the huge magnification provided by eMACSJ1341 allows us to study in detail a very rare type of galaxy."
Details of the discovery are published in Astrophysical Journal Letters. | 0.885544 | 3.991371 |
CAPE CANAVERAL, Fla. (AP) — The spigot has opened again, and Pluto pictures are pouring in once more from NASA”s New Horizons spacecraft.
These newest snapshots reveal an even more diverse landscape than scientists imagined before New Horizons swept past Pluto in July, becoming the first spacecraft to ever visit the distant dwarf planet.
“If an artist had painted this Pluto before our flyby, I probably would have called it over the top — but that”s what is actually there,” said Alan Stern, New Horizons” principal scientist from Southwest Research Institute in Boulder, Colorado.
In one picture, dark ancient craters border much younger icy plains. Dark ridges also are visible that some scientists speculate might be dunes.
One outer solar-system geologist, William McKinnon of Washington University in St. Louis, said if the ridges are, in fact, dunes, that would be “completely wild” given Pluto”s thin atmosphere.
“Either Pluto had a thicker atmosphere in the past, or some process we haven”t figured out is at work. It”s a head-scratcher,” McKinnon said in a written statement.
The jumble of mountains, on the other hand, may be huge blocks of ice floating in a softer, vast deposit of frozen nitrogen.
After several weeks of collecting engineering data from New Horizons, scientists started getting fresh Pluto pictures last weekend. The latest images were released Thursday.
Besides geologic features, the images show that the atmospheric haze surrounding Pluto has multiple layers. What”s more, the haze crates a twilight effect that enables New Horizons to study places on the night side that scientists never expected to see.
Monday marks two months from New Horizons” close encounter with Pluto on July 14, following a journey from Cape Canaveral, Florida, spanning 3 billion miles and 9 years. As of Friday, the spacecraft was 44 million miles past Pluto.
So much data were collected during the Pluto flyby that it will take until next fall to retrieve it all here on Earth. The spacecraft is operated from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, which also designed and built it.
New Horizons” next target, pending formal approval by NASA, will be a much smaller object that orbits 1 billion miles beyond Pluto. It, too, lies in the so-called Kuiper Belt, a frigid twilight zone on the outskirts of our solar system. Following a set of maneuvers, New Horizons would reach PT1 — short for Potential Target 1 — in 2019.
Johns Hopkins: http://pluto.jhuapl.edu/ | 0.811185 | 3.314769 |
Messier 61 is a galaxy that’s got it all.
I mean, c’mon. <ticks off fingers> Face-on spiral, sits in the nearest galaxy cluster to us, tons of beautiful nebulae, copious star formation, (mildly) active black hole in its core, massive star cluster sitting near that black hole, overachieving number of supernovae, and was discovered by two people on the same night except one of them very ironically thought it was a comet.
That enough for you? Let’s proceed.
Messier 61, aka M61, is a galaxy a lot like our own. It’s a spiral, roughly 100,000 light years across, with a bar (an elongated lozenge-shaped structure of stars) in its middle. It’s about 52 million light years away and is a resident of the Virgo Cluster, a sprawling collection of well over a thousand galaxies. That cluster is the center of the much larger Virgo Supercluster, which has tens of thousands of galaxies in it … including our own. So we and M61 are neighbors.
But of course you want to see it, right? Oh my yes, you do:
This gorgeousity was taken with one of the four 8.2-meter Very Large Telescope Unit Telescopes (together, the 4 UTs make up the VLT), using a camera called the FOcal Reducer and low dispersion Spectrograph 2, or FORS2, which allows the telescope to capture wide-angle shots of the sky. The image is a combination of three color filters (red, green, and blue) to mimic natural color, plus an extra layer using an H-alpha filter, which emphasizes the light from warm hydrogen.
The blue glow is the combined light of millions of high-mass, luminous stars, much brighter and hotter than the Sun. There are far fewer of them in the galaxy than lower-mass stars, but they are so bright they outshine the others. They also trace out the curved majestic spiral arms of M61; these stars are born in those arms and don’t live long, so their distribution is the same as the arms themselves.
You can see lots of pinkish-red blobs dotting the arms, too: Those are gigantic gas clouds called nebulae, from which stars are born. The stars warm the gas, causing it glow red, and the H-alpha filter really brings them out in the image.
I was amazed at the sheer number of nebulae in M61 when I saw this image, so I wasn’t surprised to find out it’s what’s called a starburst galaxy, making stars at a much higher rate than average. Once I knew that I wasn’t surprised to find there have been an unusual number of supernovae, exploding stars, seen in M61 too. If you make lots of high-mass stars they’re gonna die eventually, and when they do, bang!
Speaking of which, very near the center of M61 is a super star cluster, a stellar beehive of thousands of stars blasting out huge amounts of light, over 100 million times the Sun’s energy emission! The cluster is only a few dozen light years out from the core, which is interesting indeed: Right at the heart of the galaxy is a supermassive black hole — every big galaxy has one, including ours — so this cluster managed to form very close to this monster. The cluster looks to have been born in a vast burst of star formation about 4 million years ago.
In many galaxies where the black hole is gobbling down material, the core appears very bright, especially at colors of light like ultraviolet. It was always assumed that was the case for M61, but in fact the black hole is only a weak source of emission. The super star cluster dominates the UV emission! So it’s quite a beast.
M61 is close enough to Earth to see with binoculars. It was discovered by astronomer Barnabus Oriani on May 5, 1779. But there’s a twist: French comet hunter Charles Messier also saw it on the very same night! However, at the time, Messier though it was a comet … reasonably, as it turns out, because the Great Comet of 1779 passed right over the position of M61 at that time. Messier logged observations of M61 on the 6th and 11th of May as well, and it wasn’t until that last one that he realized he wasn’t seeing a comet.
The irony of this makes me chuckle. Messier loved finding comets (he discovered over a dozen), so much so that other fuzzy blobs in the sky irritated him. He started a catalog of them that he first published in 1774, and updated a few times. The Messier Catalog, as we now call it, contains some of the brightest and most adored objects in the sky to see with small telescopes: star ers, nebulae, and galaxies … including M61.
So he literally mistook the galaxy for a comet, years after he started his catalog to help him not mistake objects for comets, and he wasn’t the first one to see it, yet it bears his name to this day despite actively seeking to avoid observing it!
I’ll be honest; I had never heard of Oriani until researching this, but I’ve seen nearly every Messier object in the sky myself. Every amateur astronomer knows Messier’s name. Fame is weird.
So while Messier died in 1817, his name does indeed live on, as does M61. It will continue to delight astronomers for centuries upon centuries to come, and the galaxy itself will happily crank out stars and do its galactic thing for eons. Not a bad legacy for a guy who didn’t want to see it. | 0.832735 | 3.843832 |
June 27, 2019 at 4:17 pm #26006EarlKeymaster
“John Carter and the Quadcopters of Titan” has a certain ring to it. [LINK]
Dragonfly will launch in 2026 and arrive in 2034. The rotorcraft will fly to dozens of promising locations on Titan looking for prebiotic chemical processes common on both Titan and Earth. Dragonfly marks the first time NASA will fly a multi-rotor vehicle for science on another planet; it has eight rotors and flies like a large drone. It will take advantage of Titan’s dense atmosphere – four times denser than Earth’s – to become the first vehicle ever to fly its entire science payload to new places for repeatable and targeted access to surface materials.
Dragonfly took advantage of 13 years’ worth of Cassini data to choose a calm weather period to land, along with a safe initial landing site and scientifically interesting targets. It will first land at the equatorial “Shangri-La” dune fields, which are terrestrially similar to the linear dunes in Namibia in southern Africa and offer a diverse sampling location. Dragonfly will explore this region in short flights, building up to a series of longer “leapfrog” flights of up to 5 miles (8 kilometers), stopping along the way to take samples from compelling areas with diverse geography. It will finally reach the Selk impact crater, where there is evidence of past liquid water, organics – the complex molecules that contain carbon, combined with hydrogen, oxygen, and nitrogen – and energy, which together make up the recipe for life. The lander will eventually fly more than 108 miles (175 kilometers) – nearly double the distance traveled to date by all the Mars rovers combined.
Dragonfly was selected as part of the agency’s New Frontiers program, which includes the New Horizons mission to Pluto and the Kuiper Belt, Juno to Jupiter, and OSIRIS-REx to the asteroid Bennu. Dragonfly is led by Principal Investigator Elizabeth Turtle, who is based at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland. New Frontiers supports missions that have been identified as top solar system exploration priorities by the planetary community. The program is managed by the Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Planetary Science Division in Washington.
(There’s also a Xanadu region on Titan, so maybe the next step is to launch Jeff Lynne there to collect samples.)
November 27, 2019 at 10:15 am #26361ubikuberallesModerator
Well, you got ELO and NASA mentioned in your post but you left out doctor Who. Tsk. Tsk.
It’s cool that they are using a multi-rotor drone-like craft for this mission. Bold move and a bit risky since they are using unproven technology with a much more complicated mission (flight plan, objectives and so on). I would love to see the same kind of craft on Mars. It would cover a lot more ground than the Rovers ever did.
- You must be logged in to reply to this topic. | 0.897191 | 3.213611 |
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