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Ever wonder how we possibly know how far away stars and galaxies are from the earth? Obviously it involves telescopes and measurements, right? But beyond that, how does our observed data actually translate into light years? How do we know what we know?
This animation by Royal Observatory Greenwich explains the fundamental tools astronomers use to decode data from dots of light–principles like parallax and redshift. And don’t worry, nothing requires a science degree to understand because the video was built upon simple metaphors like light bulbs and fire engines.
But beyond the explanation itself, it’s remarkable how we’ve scaled the smallest of observations around us into an educated view of objects that are millions of lifetimes beyond our grasp. And it’s just as remarkable how astrophysicists can so concisely explain the concepts of the heavens in plain-person speak. Have you ever noticed, whether it’s a Discovery Channel special or a New York Times article, it’s rare that you’ll spot an interview with an astrophysicist that isn’t rich with these metaphors of scale?
Even for the smartest among us, our brains just aren’t quite big enough to conceptualize the true scale of forces working within the universe. So whether it’s through clever animations, scientific notation, or scrolling infographics, we all need the occasional mental crutch to grasp ideas larger than ourselves. Or, put differently, even the largest questions in our known universe asked by the greatest minds on our planet teeter on the clarity of good design. And maybe some bigger telescopes wouldn’t hurt. | 0.845039 | 3.016407 |
Planet capable of sustaining life finally found
Water vapour has been detected on a potentially habitable super-Earth in a world-first discovery.
The planet is called K2-18b and it's now the only known celestial body orbiting a star outside of our Solar System to have both water and temperatures that could support life.
According to The Sun, researchers from University College London analysed data from the Hubble Space Telescope and found K2-18b has water vapour in its atmosphere.
This is the first successful atmospheric detection of water on an exoplanet orbiting in its star's 'habitable zone'.
The groundbreaking discovery has been published today in Nature Astronomy.
First author Dr Angelos Tsiaras said: "Finding water in a potentially habitable world other than Earth is incredibly exciting."
He added: "K2-18b is not 'Earth 2.0' as it is significantly heavier and has a different atmospheric composition.
"However, it brings us closer to answering the fundamental question: Is the Earth unique?"
Dr Tsiaras and the rest of the UCL team developed an algorithm to analyse data that had already been taken from K2-18b's atmosphere.
The results revealed the molecular signature of water vapour as well as highlighting the presence of hydrogen and helium in the planet's atmosphere.
The researchers think that can indicate life including methane and nitrogen may be present.
However, more tests are needed to prove this.
The researchers also want to estimate cloud coverage and the amount of atmospheric water on the planet.
K2-18b orbits a cool dwarf star and is about 110 light years away from Earth in the Leo constellation.
However, its red dwarf star is quite active which means it could be exposing the planet to lots of radiation, which would make K2-18b a much more hostile place than Earth.
The super-Earth is eight times the mass of Earth and was located in 2015.
It was one of hundreds of super-Earth that were detected by Nasa's now-retired Kepler space telescope.
To qualify as a super-Earth, a planet needs to have a mass that is between those of Earth and Neptune.
Co-author Dr Ingo Waldmann said: "With so many new super-Earths expected to be found over the next couple of decades, it is likely that this is the first discovery of many potentially habitable planets.
The next generation of space telescopes, including the European Space Agency's ARIEL mission, will be able to observe atmospheres in more detail.
ARIEL is expected to launch in 2028, and aims to observe 1,000 planets in detail so it could help us gain a more accurate picture of what planet K2-18b is like.
This story first appeared in The Sun and is republished with permission. | 0.925713 | 3.501587 |
In February 1987, Neil Gehrels, a young researcher at NASA’s Goddard Space Flight Center, boarded a military plane bound for the Australian Outback. Gehrels carried some peculiar cargo: a polyethylene space balloon and a set of radiation detectors he had just finished building back in the lab. He was in a hurry to get to Alice Springs, a remote outpost in the Northern Territory, where he would launch these instruments high above Earth’s atmosphere to get a peek at the most exciting event in our neck of the cosmos: a supernova exploding in one of the Milky Way’s nearby satellite galaxies.
Like many supernovas, SN 1987A announced the violent collapse of a massive star. What set it apart was its proximity to Earth; it was the closest stellar cataclysm since Johannes Kepler spotted one in our own Milky Way galaxy in 1604. Since then, scientists have thought up many questions that to answer would require a front row seat to another supernova. They were questions like this: How close does a supernova need to be to devastate life on Earth?
Back in the 1970s, researchers hypothesized that radiation from a nearby supernova could annihilate the ozone layer, exposing plants and animals to harmful ultraviolet light, and possibly cause a mass extinction. Armed with new data from SN 1987A, Gehrels could now calculate a theoretical radius of doom, inside which a supernova would have grievous effects, and how often dying stars might stray inside it.
To understand just how supernovas affected life, scientists needed to link the timing of their explosions to pivotal events on earth such as mass extinctions or evolutional leaps.
“The bottom line was that there would be a supernova close enough to the Earth to drastically affect the ozone layer about once every billion years,” says Gehrels, who still works at Goddard. That’s not very often, he admits, and no threatening stars prowl the solar system today. But Earth has existed for 4.6 billion years, and life for about half that time, meaning the odds are good that a supernova blasted the planet sometime in the past. The problem is figuring out when. Because supernovas mainly affect the atmosphere, it’s hard to find the smoking gun,” Gehrels says.
Astronomers have searched the surrounding cosmos for clues, but the most compelling evidence for a nearby supernova comes—somewhat paradoxically—from the bottom of the sea. Here, a dull and asphalt black mineral formation called a ferromanganese crust grows on the bare bedrock of underwater mountains—incomprehensibly slowly. In its thin, laminated layers, it records the history of planet Earth and, according to some, the first direct evidence of a nearby supernova.
These kinds of clues about ancient cosmic explosions are immensely valuable to scientists, who suspect that supernovas may have played a little-known role in shaping the evolution of life on Earth. “This actually could have been part of the story of how life has gone on, and the slings and arrows that it had to dodge,” says Brian Fields, an astronomer at the University of Illinois at Urbana-Champaign. But to understand just how supernovas affected life, scientists needed to link the timing of their explosions to pivotal events on earth such as mass extinctions or evolutional leaps. The only way to do that is to trace the debris they deposited on Earth by finding elements on our planet that are primarily fused inside supernovas.
Fields and his colleagues named a few such supernova-forged elements—mainly rare radioactive metals that decay slowly, making their presence a sure sign of an expired star. One of the most promising candidates was Fe-60, a heavy isotope of iron with four more neutrons than the regular isotope and a half-life of 2.6 million years. But finding Fe-60 atoms scattered on the Earth’s surface was no easy task. Fields estimated that only a very small amount of Fe-60 would have actually reached our planet, and on land, it would have been diluted by natural iron, or been eroded and washed away over millions of years.
The crusts’ growth is one the slowest processes known to science—they put on about five millimeters every million years.
So scientists looked instead at the bottom of the sea, where they found Fe-60 atoms in the ferromanganese crusts, which are rocks that form a bit like stalagmites: They precipitate out of liquid, adding successive layers, except they are composed of metals and form extensive blankets instead of individual spires. Composed primarily of iron and manganese oxides, they also contain small amounts of almost every metal in the periodic table, from cobalt to yttrium.
As iron, manganese, and other metal ions wash into the sea from land or gush from underwater volcanic vents, they react with the oxygen in seawater, forming solid substances that precipitate onto the ocean floor or float around until they adhere to existing crusts. James Hein at the United States Geological Survey, who studied crusts for more than 30 years, says that it remains a mystery exactly how they establish themselves on rocky stretches of seafloor, but once the first layer accumulates, more layers pile on—up to 25 centimeters thick.
That enables crusts to serve as cosmic historians that keep records of seawater chemistry, including the elements that serve as timestamps of dying stars. One of the oldest crusts, fished out by Hein southwest of Hawaii in the 1980s, dates back more than 70 million years, to a time when dinosaurs roamed the planet and the Indian subcontinent was just an island in the ocean halfway between Antarctica and Asia.
The crusts’ growth is one the slowest processes known to science—they put on about five millimeters every million years. For comparison, human fingernails grow about 7 million times faster. The reason for that is plain math. There’s less than one atom of iron or manganese for every billion molecules of water in the ocean—and then they must resist the pull of passing currents and the power of other chemical interactions that might pry them loose until they get trapped by the next layer.
Unlike the slow-growing crusts, however, supernova explosions happen almost instantly. The most common type of supernova occurs when a star runs out of its hydrogen and helium fuel, causing its core to burn heavier elements until it eventually produces iron. That process can take millions of years, but the star’s final moments take only milliseconds. As heavy elements accumulate in the core, it becomes unstable and implodes, sucking the outer layers inward at a quarter of the speed of light. But the density of particles in the core soon repels the implosion, triggering a massive explosion that shoots a cloud of stellar debris out into space—including Fe-60 isotopes, some of which eventually find their home in ferromanganese crusts.
The first people to look for the Fe-60 in these crusts were Klaus Knie, an experimental physicist then at the Technical University of Munich, and his collaborators. Knie’s team was studying neither supernovas nor crusts—they were developing methods for measuring rare isotopes of various elements—including Fe-60. After another scientist measured an isotope of beryllium, which can be used to date the layers of the crusts, Knie decided to examine the same specimen for Fe-60, which he knew was produced in supernovas. “We are part of the universe and we have the chance to hold the ‘astrophysical’ matter in our hand, if we look at the right places,” says Knie, who is now at the GSI Helmholtz Center for Heavy Ion Research.
Knie’s new tool gives scientists the ability to date other, possibly more ancient, supernovas that may have passed in the vicinity of Earth, and to study their influence on our planet.
The crust, also plucked from the seafloor not far from Hawaii, turned out to be the right place: Knie and his colleagues found a spike in Fe-60 in layers that dated back about 2.8 million years, which they say signaled the death of a nearby star around that time. Knie’s discovery was important in several ways. It represented the first evidence that supernova debris can be found here on Earth and it pinpointed the approximate timing of the last nearby supernova blast (if there had been a more recent one, Knie would have found more recent Fe-60 spikes.). But it also enabled Knie to propose an interesting evolutionary theory.
Based on the concentration of Fe-60 in the crust, Knie estimated that the supernova exploded at least 100 light-years from Earth—three times the distance at which it could’ve obliterated the ozone layer—but close enough to potentially alter cloud formation, and thus, climate. While no mass-extinction events happened 2.8 million years ago, some drastic climate changes did take place—and they may have given a boost to human evolution. Around that time, the African climate dried up, causing the forests to shrink and give way to grassy savanna. Scientists think this change may have encouraged our hominid ancestors as they descended from trees and eventually began walking on two legs.
That idea, as any young theory, is still speculative and has its opponents. Some scientists think Fe-60 may have been brought to Earth by meteorites, and others think these climate changes can be explained by decreasing greenhouse gas concentrations, or the closing of the ocean gateway between North and South America. But Knie’s new tool gives scientists the ability to date other, possibly more ancient, supernovas that may have passed in the vicinity of Earth, and to study their influence on our planet. It is remarkable that we can use these dull, slow-growing rocks to study the luminous, rapid phenomena of stellar explosions, Fields says. And they’ve got more stories to tell.
Lead composite image credit: Pinwheel-Shaped Galaxy by NASA, ESA, The Hubble Heritage Team, (STScI/AURA) and A. Riess (STScI) and Red Sea Coral Reef by Wusel700
This article was originally published in Nautilus magazine on March 19, 2015. | 0.818356 | 4.029568 |
The detection of X-rays coming from Pluto is challenging scientists to understand more about the space surrounding the best-known object in the outer solar system.
While NASA’s New Horizons spacecraft was speeding toward and beyond Pluto, NASA’s Chandra X-ray Observatory—in orbit back at Earth—was aimed several times on the dwarf planet and its moons, gathering data that the missions could compare. Each time Chandra pointed at Pluto—four times in all, from February 2014 through August 2015—it detected X-rays coming from the small planet.
That was somewhat surprising, given that Pluto—cold, rocky and without a magnetic field—has no natural mechanism for emitting X-rays.
“We’ve just detected, for the first time, X-rays coming from an object in our Kuiper Belt, and learned that Pluto is interacting with the solar wind in an unexpected and energetic fashion,” says Carey Lisse, an astrophysicist at Johns Hopkins University Applied Physics Laboratory, who led the Chandra observation team with APL’s New Horizons co-investigator Ralph McNutt. “We can expect other large Kuiper Belt objects to be doing the same.”
Pluto is the largest object in the Kuiper Belt, a vast population of small, distant bodies orbiting the sun. The belt extends from the orbit of Neptune, 30 times the distance of Earth from the sun, to about 50 times the Earth-sun distance.
Lisse, who first detected X-rays from a comet two decades ago, knew that X-rays from Pluto—though not likely—were possible. The interaction between gases surrounding planetary bodies and the solar wind—the constant streams of charged particles speeding out from the sun—can create X-rays, which are high-energy electromagnetic waves with a very short wavelength.
New Horizons scientists wanted to learn about the interaction between Pluto’s atmosphere and the solar wind. The spacecraft carries an instrument designed to measure that activity up-close, the aptly named Solar Wind around Pluto. Scientists are using SWAP data to craft a picture of Pluto with a very mild, close-in bow shock, where the solar wind first “meets” Pluto (similar to a shock wave that forms ahead of a supersonic aircraft) and a small wake behind the planet. The immediate mystery is that Chandra’s readings on the brightness of the X-rays are much higher than would be expected from the solar wind interacting with Pluto’s atmosphere.
“Before our observations, scientists thought it was highly unlikely that we’d detect X-rays from Pluto, causing a strong debate as to whether Chandra should observe it at all,” says coauthor Scott Wolk of the Harvard-Smithsonian Center for Astrophysics. “Prior to Pluto, the most distant solar system body with detected X-ray emission was Saturn’s rings and disk.”
Although Pluto is releasing enough gas from its surprisingly stable atmosphere to make the observed X-rays, in simple models for the intensity of the solar wind at the distance of Pluto, there isn’t enough solar wind flowing directly at Pluto to make them.
Researchers suggest several possibilities for the enhanced X-ray emission from Pluto. One is that there is a much wider and longer tail of gas trailing Pluto than New Horizons found with SWAP. Another is that interplanetary magnetic fields are focusing more particles than expected from the solar wind into the region around Pluto. A third is that the low density of the solar wind in the outer solar system could allow formation of a doughnut, or torus, of neutral gas centered on Pluto’s orbit.
That the Chandra measurements don’t quite match up with New Horizons up-close observations is the benefit—and beauty—of an opportunity like the New Horizons flyby.
“When you have a chance at a once in a lifetime flyby like New Horizons at Pluto, you want to point every piece of glass—every telescope on and around Earth—at the target,” McNutt says. “The measurements come together and give you a much more complete picture you couldn’t get at any other time, from anywhere else.”
The study is published in the journal Icarus. APL designed, built, and operates New Horizons for NASA’s Science Mission Directorate. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations.
Source: Johns Hopkins University | 0.851461 | 4.094061 |
IMMANUEL KANT (April 22, 1724 – February 12, 1804)
German philosopher, anthropologist, and key thinker of the Enlightenment.
- Produced over 50 philosophical volumes, including his masterpiece Critique Of Pure Reason (1781), as well as The False Subtlety Of The Four Syllogistic Figures (1762) and The Only Possible Argument In Support Of A Demonstration Of The Existence Of God (1763).
- Established a comprehensive branch of philosophy based on the “Copernican Revolution,” which connected the external world to the perception of those viewing it.
- Winner of the Berlin Academy Prize in 1754.
Baptized Emanuel Kant (he changed the spelling of his name later in life), Kant was born in 1724 in eastern Prussia (present-day Germany); his hometown, Königsberg, is now part of Russia. As a boy, he was an excellent student who received a strict religious education that emphasized the literal interpretation of the Bible and fluency in Biblical languages over liberal arts subjects like science and history. When his family recognized his scholarly aptitude, he was sent to school, eventually attending the University of Königsberg, where he was introduced to German and British philosophy, science, mathematics, as well as recent advances in physics introduced by Isaac Newton. After his father had suffered a stroke, Kant supported his family by working as a tutor, and continued to pursue his studies in his free time.
In 1749, at the age of 25, Kant published his first work, Thoughts on the True Estimation of Living Forces, a direct outgrowth of his university studies in which he defended a position of metaphysical dualism while arguing against the beliefs of many of his contemporary German philosophers. Other works followed, in both philosophy and science (a distinction not made as sharply in the 18th century as it is now). Interestingly, although Kant is now thought of as one of the more difficult and esoteric German philosophers whose work is full of complex concepts, one of his early contributions was the Nebular Hypothesis. In 1755’s Allgemeine Naturgeschichte, rarely translated into English because it is now of interest principally to historians of science, Kant refined Emanuel Swedenborg’s 1734 hypothesis that the solar system had begun as a cloud of gaseous material, which condensed into the “clumps” of the sun and planets. Kant concluded that for this cosmological model to work, those clouds—nebulae—must rotate, with gravity gradually crunching them down into the solid state of the solar system. This remains the most widely accepted cosmological model today, with modifications and tweaks made to incorporate expanding view of the universe. What’s fascinating is that Kant and Swedenborg were able to come to this conclusion hundreds of years before satellites, probes, and other tools of modern astronomy.
In that same year, Kant moved away from his tutoring job to become a more highly paid and respected university lecturer. Throughout his 30s, he wrote a variety of philosophical texts dealing with logic, emotion, and the existence of God. At the age of 45, he was made a full professor of logic and metaphysics, becoming caught up both in teaching and the response to his written work so far. Consequently, he didn’t publish again for 11 years. When he finally did, the result was Critique of Pure Reason, the most impressive work of philosophy by a single author—though perhaps because of its immense size, or possibly because Kant had been silent so long, it had little immediate impact.
The first of Kant’s “three critiques,” Pure Reason is difficult to sum up. He begins by rejecting the recent conclusions of his friend and fellow philosopher David Hume, whose work argued that ideas all begin as representations of sensory (i.e., physical) experience. Kant claimed that we could have knowledge not based on empirical experience—indeed, that much important and applicable knowledge had begun as such—and spent 800 pages proving his argument. The book is dense, filled with thought experiments and specialized language that doesn’t translate well into English.
The work rejuvenated Kant’s interest in publishing or maybe just gave impetus to his writing. The 1780s were a busy time for him, with the publication of his first works on moral philosophy as well as his second and third critiques (Critique of Practical Reason and Critique of Judgment). Naturally, he attracted a good deal of criticism, but his influence was undeniable, and the school of German Idealism formed with his pupils and younger colleagues. A true workaholic, he never married. He did, however, have a big following; when he died shortly before his 80th birthday, regularly publishing until the last year of his life, he was mourned by many. | 0.820307 | 3.021267 |
The frigid, faraway body that NASA's New Horizons spacecraft will zoom by 18 months from now may actually be a cluster of small objects, new observations suggest.
New Horizons — which performed the first-ever flyby of Pluto in July 2015 — will have another close encounter on Jan. 1, 2019, this time with a little-studied object called 2014 MU69.
Mission scientists recently had a chance to learn more about 2014 MU69, which lies about 1 billion miles (1.6 billion kilometers) beyond the orbit of Pluto and is thought to be 12 to 25 miles (20 to 40 km) wide. On the night of June 2, MU69 crossed in front of a distant star in a 2-second "occultation" visible from a narrow band of land and sea that stretched from the Indian Ocean through South Africa to southern Argentina and Chile. [Destination Pluto: NASA's New Horizons Mission in Pictures]
So New Horizons team members set up shop in various spots along the occultation path and pointed their telescopes skyward. They ended up taking more than 100,000 images of the occulted star, none of which captured 2014 MU69 itself, NASA officials said.
"These results are telling us something really interesting," New Horizons principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, said in a statement.
"The fact that we accomplished the occultation observations from every planned observing site but didn’t detect the object itself likely means that either MU69 is highly reflective and smaller than some expected, or it may be a binary or even a swarm of smaller bodies left from the time when the planets in our solar system formed," Stern added.
The team may be able to narrow down these possibilities soon. MU69 will make two more stellar occultations this month: one on July 10 and the other on July 17.
New Horizons scientists plan to use NASA's Stratospheric Observatory for Infrared Astronomy — a 747 jet equipped with a 100-inch (2.5 m) telescope — to observe the July 10 event. The main goal is to hunt for debris around 2014 MU69 that could pose a danger to New Horizons during the upcoming flyby, agency officials said.
New Horizons team members will observe the July 17 occultation from southern Argentina, gathering data that could help nail down 2014 MU69's size. Scientists will also use NASA's Hubble Space Telescope to watch that event, searching for hazardous debris.
The $700 million New Horizons mission launched in January 2006. More than nine years later, on July 14, 2015, the probe gave humanity its first up-close looks at Pluto, revealing a startlingly complex and diverse world with vast nitrogen-ice plains and towering mountains of water ice.
The upcoming flyby of 2014 MU69 is the centerpiece of New Horizons' extended mission, which NASA officially approved last year.
Follow Mike Wall on Twitter @michaeldwall and Google+ . Follow us @Spacedotcom , Facebook or Google+ . Originally published on Space.com . | 0.881187 | 3.522573 |
Mysterious alignment of supermassive black holes discovered in the distant universe.
Astronomers have been shocked by new deep radio imaging which has revealed that supermassive black holes in a region of the distant universe are all spinning out radio jets in the same direction. The bizarre findings are totally unexpected -- based on our current understanding of cosmology.
A new study bringing science a step closer to understanding antimatter.
Scientists are developing new numerical models to better understand why we live in a universe composed mostly of matter rather than antimatter. Existing cosmological theory tells us that equal amounts of matter and antimatter were made in the big bang 13.8 billion years ago, and the laws of physics show that matter and antimatter annihilate each other if they come into contact. So that raises the question: why didn’t the universe explode and cease to exist immediately and why do we live a universe made of matter rather than antimatter?
The strange system challenging existing models on dark matter and hypervelocity stars.
Astronomers have discovered a strange star system on the outskirts of our Milky Way Galaxy travelling at almost our galaxies escape velocity. The discovery challenges existing hypothesis that hypervelocity stars are flung onto their high speed trajectories by the supermassive black hole at the galactic centre.
New study explores links between cosmic rays and galaxy formation
New computer simulations indicate that cosmic rays – high speed subatomic particles produced in supernovae explosions -- may play a vital role in the formation of galaxies and galaxy clusters. The findings will help scientists trying to understand how galaxies are made which is among the greatest problems facing modern astrophysics.
The show notes for SpaceTime with Stuart Gary podcast
Subscribe on YouTube | 0.812613 | 3.673216 |
April 27, 2017
Do crustal blocks slide around?
According to planetary scientists, plate tectonic activity on Mars is similar to what happens on Earth. Studies undertaken by the University of California Los Angeles suggest that: “Mars is at a primitive stage of plate tectonics. It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth.”
Other theories about how Mars changes over geologic time indicate that the volcanoes located in Tharsis Montes might not be extinct after all. The four gigantic craters are near one another—three of them run in a chain, so scientists think that they must have been created in the same way that standard theories explain crater chains.
According to a paper that appeared in Geophysical Research, Olympus Mons, Ascraeus Mons, Pavonis Mons and Arsia Mons could have a moving column of magma beneath them.
Conventional theories state that volcanoes on Earth form when the plates that make up Earth’s crust move over upwelling magma plumes. Since rising magma naturally seeks out the weakest fractures, allowing it to erupt onto the surface, lava deposits build up and create steep-sided mountains.
On Mars, however, there is no evidence that the crust moves. No plate boundaries exist, despite speculations about the formation of the Valles Marineris canyon system. Previous Picture of the Day articles stress that Valles Marineris is an electrical scar, and does not adhere to common interpretations of canyon formation on Earth.
In order to explain the Tharsis anomaly, the authors of the Geophysical Research paper postulate that the plume of magma is what moved rather than the crust: “We thought we could take what we learned about lava flow features on Hawaiian volcanoes and apply it to Martian volcanoes to reveal their history.”
Information provided by the Mars Reconnaissance Orbiter indicates that those ideas about lava flows should be permanently discounted. The principle of using Earth geology to explain Martian areology is what causes researchers to misconstrue what they see when they examine images of Valles Marineris.
In previous Picture of the Day articles about Martian volcanoes, it was pointed out that the shapes of the escarpments and the surrounding topography indicates that they could have been made by enormous plasma discharges that impacted the planet. The force of the electric current raised giant mounds and carved out their distinctive calderas.
As Electric Universe guru, Wal Thornhill points out: “Olympus Mons, 25 kilometres high, is NOT the highest volcano in the Solar System. It is a giant raised electrical blister with characteristic superimposed circular craters at the summit. It is the kind of blister seen on metal lightning arrestor caps after a strike.”
If electric currents of such magnitude influenced the planet Mars on a global scale, could they have done something similar on Earth? It is the theory of plate tectonics and its relationship to volcanism on our planet that should be reconsidered, rather than inventing a new theory because new observations do not support the old one. | 0.840818 | 3.782009 |
From QuantaMag by Praddep Mutalik
A method for estimating distances in sailing and astrophysics helps explain why riding on buses and boats can make us nauseous.
This month’s Insights puzzle was inspired by a new way to determine the value of the Hubble constant, which quantifies how rapidly the universe is expanding by measuring the distance to a pair of colliding neutron stars.
This method opens up the possibility of significantly improving the accuracy of distance measurements to faraway astronomical objects.
We recalled that, for centuries, surveyors have used a method called triangulation to calculate the distance to an object without physically traveling to it.
This triangulation method, which can still be used for nearby astronomical objects, uses basic trigonometry to produce accurate distance estimates based on angles measured to the object from two different points a known distance apart.
This was the basis for our first problem.
You are sailing on the ocean and spot a bright light from a lighthouse due south.
You sail on an easterly course for 30 nautical miles.
You get bearings on the lighthouse again and find that it is now 53.13 degrees south of west.
How far was the lighthouse from you when you first spotted it? How far is it from you now?
As Ty Rex pointed out, we have to assume plane geometry here because the answers vary with latitude on a spherical surface, especially close to the poles (as readers who know about the famous “color of the bear” puzzle will recognize).
This should not be a problem in the middle latitudes of most planet-size objects given the small distances specified.
Here’s the answer in Ty Rex’s words:
The right-angled triangle formed by the initial and final positions and the lighthouse is similar to the famous (3,4,5) triangle (note that tan 53.13 ~ 4/3), with the path of the boat being on the “3” leg.
Hence the initial distance from the lighthouse is 40 nautical miles, and the final distance is 50 nautical miles.
The above problem assumes that our measurements of the boat’s traveled distance and our angular bearings on the lighthouse are accurate, which they would be if we used the accurate clocks, speed indicators and theodolites that we have on Earth.
However, astronomical distance measurements are affected by several sources of uncertainty, so in our second problem we assumed some uncertainty in the distance and angle measurements, and then tried to figure out how much triangulation helped.
Senior Editor Lenny Rudow as he walks through the basic steps on how to triangulate your position on the water when your technology and electronics decide to fail.
Using a compass, a pair of parallel rulers, a pencil, a map, and your eyes, these tips will help you to determine your exact position.
Let’s revisit the scenario of Problem 1.
Assume that you live on a planet on which there is a phenomenon of “optical wind” that causes lensing effects so that you can be sure that your estimates of the direction of an object are accurate only within ±2 degrees.
So all you can say is that the lighthouse is somewhere between 2 degrees west of south and 2 degrees east of south.
Also, you know (or think you know) how intrinsically bright the source of the light is — it is a “standard candle” — and from this you can infer its distance from you to an accuracy of ±5 percent.
Based on this, you can narrow down the area in which this lighthouse is situated.
How large is this area?
Now suppose you triangulate as before.
With the aid of the optical wind, you sail 30 nautical miles (which you can measure accurately, of course) and then again find the lighthouse to be 53.13 degrees south of west, this time with an error of ±2 degrees.
You can also infer the distance to the lighthouse with ±5 percent accuracy.
By triangulating this new measurement with your previous one, you can narrow down the area in which the lighthouse is situated.
How much reduction can you achieve?
The original area of uncertainty lies between the two 4-degree sectors of two concentric circles with radii of 38 and 42 nautical miles (a sector of a circle is the portion of a circle bounded by two radii and an arc).
It is easy to calculate the difference in area between these two sectors using the formula for the area of a sector, which is simply 1/2r²q, where r is the radius and q the angle in radians.
The answer comes out to be 11.17 square nautical miles.
As Ty Rex noted, we can approximate this figure by a rectangle centered 40 nm south of the initial boat position.
This rectangle has a length of 4 nm and a width of 2.79 nm (2 × 40 × tan 4°), which gives an area of 11.17 square nm and differs from the actual area only in the third decimal place, showing that this simplification is justified.
If we do the same thing with the area of uncertainty from the second measurement, we have two overlapping rectangles with common centers tilted from each other at an angle of 53.13 degrees (see figure below).
The original rectangle (A) has diagonals 4.88 nm long, whereas the second rectangle (B) has sides of 5 nm and 3.49 nm with the long side falling in almost exactly the same direction as the diagonal of rectangle A in the northeast to southwest direction.
This means that the long side of rectangle B completely overlaps this diagonal, but the short side leaves two small triangles uncovered at the northwest and southeast ends of the other diagonal.
These two uncovered triangles have a combined area of 1.14 square nm in which the location of the lighthouse is excluded, giving an improvement in uncertainty of about 10.2 percent.
This is a slight improvement in our knowledge of the location, but certainly not a very dramatic reduction in the area of uncertainty, thanks to the large measurement errors involved.
In astronomy, the largest distance we can use is the major diameter of Earth’s orbit, which, though huge on terrestrial scales, is much too puny for objects that are light-years away.
A far more dramatic reduction in uncertainty is seen in a process analogical to triangulation that is an inbuilt part of how we learn about the world, which I called “cognitive triangulation.” In cognitive triangulation, we pay special attention when the same answer emerges from two independent methods, strengthening the conclusions of both and reinforcing our faith in the reliability of our conclusions.
This is a process that has helped us build the entire edifice of scientific knowledge.
One way all of us use cognitive triangulation to learn about the world is by comparing and integrating the information coming from two different sense modalities.
This leads to our third question.
courtesy of Captain Lang sailing tutorials
What does cognitive triangulation between sense modalities have to do with motion sickness?
Many commenters accurately described the proximate cause for this as the cognitive dissonance between the information coming from the sense organs in the inner ear (the semicircular canals) and the eyes, and some even described how you can lessen or avoid motion sickness.
Here is a nice description by Alex MacDonald:
When experiencing motion sickness on, say a ship, you are feeling the intense failure of your body and brain to triangulate your physical position and its movement using the sensors in your inner ear which are effectively an accelerometer and your vision — two separate mechanisms which should produce the same measurement.
If you are observing primarily your surroundings on the ship itself — say in a stateroom — they will disagree.
Your eyes show you to be still and your inner ear tells you you are moving because the ship is.
This dissonance produces motion sickness.
If you follow the well known advice to look to the horizon your vision will now confirm the entire ship to be moving as your balance mechanism knows, and the two systems more nearly agree, reducing the discomfort.
Drivers in cars trend to be less sick than passengers because the driver has additional feedback from his control of the wheel and throttle and is more likely to be visually focused at a greater distance, also reducing the body’s feedback dissonance.
This is accurate, but why does cognitive dissonance induce nausea and vomiting?
What, in the language of philosophers and evolutionary biologists, is the ultimate cause?
As Anurag Reddy first mentioned, this reaction is hypothesized to take place because the brain “assumes” that the body has been poisoned.
In fact, the vomiting in motion sickness is induced by the same area of the brain — the chemoreceptor trigger zone in the medulla — that causes vomiting in response to poisons.
This response has probably been programmed by evolution: If two normally reliable sensory systems of the brain give information that is drastically different, in the absence of trauma or illness, it is probable that one of them, or both, are malfunctioning.
In the past, when there were no warning labels on foods, and no toxicology databases to consult, one of the most common reasons for this was likely the unwitting ingestion of unknown poisons.
If the symptoms were severe, the only chance of being saved would have been to expel as much of the as yet unabsorbed poison as possible.
Hence, when the brain believes the body has been poisoned, it is programmed to try to eject all the contents of the gastrointestinal tract as soon as it can.
It may make you even more miserable, but if you were poisoned, it could very well save your life.
If not, it’s just a temporary discomfort.
Recall how many times you’ve been sick in response to food poisoning even with today’s food-safety regulations.
This response has probably saved millions of lives throughout evolutionary history.
But can’t the brain distinguish between motion sickness and poisoning?
Such an ability could evolve, but motion sickness has only become common with the relatively recent advent of high-speed travel.
A rewiring change in the brain to distinguish motion sickness from poisoning would only be fixed in evolution if there was an appreciable advantage in survival or fertility for people who could distinguish between the two.
Considering that motion sickness is rarely, if ever, fatal, this could take many hundreds of thousands of generations.
Meanwhile, it’s always a great evolutionary strategy for our brains to imagine the worst and protect us from it, so we seem to be stuck with motion sickness for the foreseeable future.
Thank you for all your interesting comments.
Please keep them coming.
Besides the comments referenced above, I enjoyed reading about the personal experiences and the cognitive triangulation “aha!” moments of readers such as Ty Rex, Randy Tompson and Jonathan J. | 0.862581 | 3.536148 |
Short Introduction in Visual Observation of Deep Sky Objects
Following I want to give a short overview about the topic "Visual Observation of Deep Sky Objects". A bit more detailed is the paper Einführung in die visuelle Deep-Sky Beobachtung ("Introduction in Visual Observation of Deep Sky Objects") of Thomas Jäger, Wolfgang Steinicke & Hans-Jürgen Wulfrath, which is only available in German!
How wants to make notes of the observed objects, might find this blank protocol (only in German!) as template useful.
What do we understand by "Deep Sky"?
Deep Sky Objects are in general all objects located outside of our solar system. Basically we distinguish between galactic and extragalactic objects, so objects within & outside of our Galaxy. Following object types are visually of special interest:Galactic Objects:
- (Variable) Stars
- Binary- & Multiple Star Systems
- Open Clusters
- Globular Clusters
- Emission-, Reflection- and Dark Nebulas
- Planetary Nebulas
- Galaxies or Galaxy Groups
Partially there are also objects within other galaxies observable. These are mainly emission nebulas (e.g. NGC 604 in Messier 33), large star associations (e.g. NGC 206 in Messier 31) or bright globular clusters (Mayall II in Messier 31).
Besides the mentioned types there are sometimes Novae or Supernovae visible, which mostly appear as stellar objects. Supernovae are not seldom present in distant galaxies.
Observing the sky visually might be one of the oldest tasks in astronomy. While formerly observations were fundamental (the New General Catalogue, in short NGC, is based solely on visual observations), these are today more a personal journey of discovery. Experiencing the miracles of the cosmos is appealing for most of us. Some do this in a more relaxed way, others prefer it more sportingly. But in the end, everyone can choose its own way to have fun and get diverted from the daily routine. Besides the pure visual observation a documentation of the seen is for many observers an important part. Short notes, detailed reports or object descriptions, but also sketches are common, which can show impressively the personal development over the years.
Do I need a telescope for observing?
Not necessarily, because there a some objects already observable with the naked eye. Under halfway dark skies objects like Messier 31 (Galaxy, And) or Messier 44 (Open Cluster, Cnc) are obvious. The open cluster Messier 45 (Tau) is visible even from the city without any equipment.
With binoculars there are a lot of objects reachable, so that you can be busy whole nights. A dark sky is of course highly preferable, however even under suburban skies many objects, including some brighter galaxies from the Messier catalogue, are feasible. Therefore I can highly recommend to make some attempts with binoculars. Even I was really surprised, what an 8x40 binoculars can show under NELM 5.0 mag skies.
For fainter objects or details telescopes with an appropriate aperture are a must. Which aperture you choose in the end, depends from several factors, which will be not discussed at this point.
What can I see?
A very good question, which is hard to answer. From my own experience I can say, that perception can differ extremely. I have met laypeople, who can easily see the dust lane in the galaxy NGC 891 with 8 inch for sure, others had basically problems to see this galaxy at all. At this point I want to keep this topic short and would recommend everyone to meet amateurs in the immediate vicinity to get a tentative possibility for discovering the sky. Basically the sky offers a lot of objects, which can be discovered and can reveal details depending on aperture. | 0.861482 | 3.719987 |
The first exoplanets were all found using the radial velocity method of measuring the “wobble” of a star — movement caused by the gravitational pull of an orbiting planet.
Radial velocity has been great for detecting large exoplanets relatively close to our solar system, for assessing their mass and for finding out how long it takes for the planet to orbit its host star.
But so far the technique has not been able to identify and confirm many Earth-sized planets, a primary goal of much planet hunting. The wobble caused by the presence of a planet that size has been too faint to be detected by current radial velocity instruments and techniques.
However, a new generation of instruments is coming on line with the goal of bringing the radial velocity technique into the small planet search. To do that, the new instruments, together with their telescopes. must be able to detect a sun wobble of 10 to 20 centimeters per second. That’s quite an improvement on the current detection limit of about one meter per second. | 0.866058 | 3.556282 |
How well was the gravitational field of Philae's landing spot known before the landing? I am referring to the absolute value of the pull, the direction of pull, and the tidal forces.
Rosetta had earlier this year been doing a triangular pattern of flybys to see how much the comet's mass would deviate it from a straight-line path.
According to this article they had a mass estimate with 10% uncertainty, which tells the overall gravitation to the same uncertainty if 67P is considered as a point mass. They may have refined the mass estimate since then, without Wikipedia keeping up. ;)
With a reasonably good model of the 3-D geometry of the comet body, and assuming relatively homogenous makeup, they could certainly make an estimate of the gravitational force on Philae as it approached the landing site. Both the model and the homogeneity would be subject to some uncertainty as well, though, so -- and this is just me guessing here -- there might be more like 15%-20% uncertainty in the estimate. | 0.821225 | 3.084644 |
Four decades after NASA’s Viking landers acquired humanity’s first view of the surface of Mars, a planet whose reality lived in the imaginations of skywatchers for millennia, a definitive smoking gun for microbial life there still eludes scientists.
Since the two Viking missions turned up no concrete evidence for life on Mars, at least according to the interpretations of most astrobiologists, all landers dispatched to the red planet have carried no similar instrumentation for a direct detection of living microbes.
Mars missions since Viking have followed the trail of water, seeking evidence that Mars was once habitable. The latest results obtained by NASA’s Curiosity rover point to the answer to that question being yes.
NASA last week celebrated the 40th anniversary of the Viking 1 probe’s touchdown on Mars on July 20, 1976, becoming the first lander to reach the Martian surface and return images and scientific data.
The twin Viking 2 lander reached Mars a few weeks later on Sept. 3.
“We ended up with more questions than we had when we formulated that mission,” said Ellen Stofan, NASA’s chief scientist, and daughter of a member of the Viking team.
Viking was NASA’s boldest robotic mission to date, with two pairs of landers and orbiters each launched aboard Titan-Centaur rockets from Cape Canaveral three weeks apart in August and September 1975.
Each spacecraft included two parts, with the descent probe designed to detach once the carrier module slipped into orbit around the red planet. Viking 1 was originally due to land July 4, 1976, on the 200th anniversary of U.S. Declaration of Independence.
But engineers looking over images from the Viking 1 orbiter deemed the planned landing site unsafe, prompting quick thinking to find another target for the lander.
Using a heat shield, parachutes and throttled rocket thrusters, Viking 1 reached the Martian volcanic plain at Chryse Planitia, then beamed to Earth the first images from the planet.
Equipped with eyes on the ground, scientists immediately began piecing together Mars’ geologic puzzle, a thrilling, but sometimes frustrating, process that continues to this day.
“To the geologists that worked on this mission, right away they could start understanding that that hill on the distant horizon was actually the rim of an impact crater, (and) that those rocks across the surface were probably excavated and dropped onto the surface when that crater formed,” Stofan said.
Carrying a complex suite of instruments to look for microbial life, measure seismic activity and weather, and study the properties of Martian rocks and soils, the Viking landers tried to do it all.
“Viking is one the greatest missions that NASA has ever undertaken,” said Roger Lanius, a former NASA chief historian who is now a senior official at the Smithsonian Institution.
Originally dubbed Voyager — not the famed outer solar system probes — the tandem Mars mission was initially slated to launch on a huge Saturn 5 rocket. The hefty payload consisted of an orbiter and a lander that would pave the way for follow-on human missions, and the mission would have cost $2 billion in 1967 dollars, according to Erik Conway, the resident historian at NASA’s Jet Propulsion Laboratory.
That is more than $14 billion at today’s dollar value, a cost deemed unaffordable in the wake of the expensive Apollo moon landing program.
The downsized Viking program cost NASA about $1 billion in the 1970s, equivalent to around $4 billion today.
Each lander launched piggyback on the Viking orbiters, then separated to streak through the Martian atmosphere protected by an ablative cork-like heat shield. A 53-foot (16-meter) diameter polyester parachute and three hydrazine-fueled terminal descent thrusters helped slow the three-legged lander’s speed through the plant’s rarefied atmosphere, and a radar guided the plutonium-powered craft to its landing site.
Each lander had two general purpose computer channels, each with storage capacity equivalent to 18,000 words. The spacecraft recorded science data to a tape recorder for long-term storage before eventual transmission back to Earth
The stationary probes made groundbreaking discoveries about the history of Mars, including clues indicating the planet’s atmosphere may have leaked into space, driving climate change. The landers also reported on Martian weather and seasons.
But Viking’s most ambitious experiment was to search for life, and the results deflated hopes that the mission would find iron-clad evidence that microbes inhabit the alien world.
“Viking, of course, had a very public role in trying to determine whether or not there was some biological material they might encounter on the red planet,” Lanius said last week at a Viking 40th anniversary celebration at NASA’s Langley Research Center in Virginia. “That was a major part of the mission, not the only part by any means … but from the public’s perspective, I think the life story is really important.”
Lanius thinks scientists may have over-sold the potential discovery of active life in the run-up to Viking.
Carl Sagan, the famous celebrity-astronomer, was a member of the Viking science team, and the idea for the highly-rated Cosmos television series was hatched during his time on the Viking mission.
Nevertheless, Lanius argues the Viking life experiments’ inconclusive results dampened the spirits of researchers and the public, and was one of several reasons NASA did not send another mission to Mars for 17 years.
“It was played up celebrity scientists like Carl Sagan, who thought they were going to find something and ballyhooed it on a regular basis including on Johnny Carson (The Tonight Show) at night,” Lanius said last week.
“What we found was apparently nobody home,” said Penny Boston, director of NASA’s Astrobiology Institute. “That was a big shock, at least to me, as then a member of the public who was sort of expecting — naively, more or less — instant results. I wanted to hear that year stuff was living. It was giving us evidence of that. So this was a really big bummer.
“I was sort of set aback,” Boston said. “I was thinking, ‘Gosh, I want to work in exobiology, as we called it at the time, and now it seems like it’s just a pile of rocks, and there’s no life there at all.'”
The Viking results “really put a dark cloud over mission thinking for a long time,” Boston said.
The biological package on each lander included three instruments, each tackling the life question differently. One experiment sought signs of carbon-based organisms, and another tried to detect metabolic processes. Both returned a negative finding.
A third instrument, called Labeled Release, injected nutrients into a radioactive solution with Martian soil, creating a culture that could be monitored for growth. The objective was to look for carbon dioxide or methane gas bubbles released by microbes, a process similar to the way inspectors on Earth check the quality of drinking water.
The results of the that bio-investigation are still open to interpretation, said Gilbert Levin, a former sewage engineer who designed the Labeled Release experiment.
In fact, to Levin, the outcome of his experiment is crystal clear.
Take Martian soil, put it in a sealed test chamber, douse it with a radioactive fluid and organic nutrients, then eureka?
“Here is gas streaming out immediately,” Levin recalled. “We were so excited. We sent out and got champagne and cigars.”
Each lander then carried out the same experiment with a lifeless control sample irradiated and heated to scorching temperatures. And?
“Much greater than a 3-sigma difference,” the 92-year-old Levin said last week, meaning that something was very different about the freshly-sourced Martian soil. “We clearly had now satisfied the pre-mission requirements for the detection of life.”
Levin said there was a “modest” difference in the experiment’s signature on Mars and the result of a similar measurement made on soil collected from California, which he said adds another check to the scorecard favoring an affirmative result for life.
While most scientists acknowledge the results of Viking’s Labeled Release experiment were consistent with active microbial life, the lack of supporting data from the landers’ other instruments threw a shade of doubt over the findings. For example, outgassing of oxygen from the Martian soil detected by Viking’s gas chromatograph is most easily explained by a chemical reaction, not microorganisms, scientists concluded.
“It showed us really how little we did understand about biology at the time,” Boston said. “This was not the fault of the community. The best science of the time was put into that mission. Of course, it (also) showed us how little we knew about Mars.”
Viking found no clear yes/no answer to the life question, Boston said.
“The conclusion by the principal experimenters (was that) a biological interpretation of the results was unlikely,” said Joel Levine, a professor of applied science at the College of William and Mary, and a former member of the Viking science team at NASA’s Langley Research Center.
“One of the criticisms that one could level at the biological package is that, in retrospect, there were clear logical gaps that were left hanging,” Boston said.
NASA did not send another robot toward Mars until 1992, when the Mars Observer orbiter blasted off from Florida. But that spacecraft was lost three days before reaching Mars, and the next successful red planet probe was Mars Pathfinder, the first in a series of NASA rovers that touched down July 4, 1997, 21 years after Viking 1’s original landing date.
Many scientists blame the long gap between Mars missions on the sour taste left by Viking’s discovery of an apparently barren world, blowing up fantastical expectations that microbes would be easy to unroot and analyze on another planet.
“Of course, there were other reasons why we didn’t go back with a successful mission to Mars for 20 years, but this failure of instant gratification, where maybe we thought that it was easier to find life than it appears to have been, was a definite component,” Boston said.
Conway, the JPL historian, said the space agency’s science budget was under pressure in the late 1970s to help pay for development of the space shuttle. In the 1980s, the Reagan administration backed large astrophysics programs — particularly the Hubble Space Telescope — at the expense of planetary science, he said.
“The gap would not have been as bad as it turned out to be had Mars Observer worked, but there are very specific political reasons that there was almost no funding for planetary science, except for Galileo (the Jupiter orbiter), during that timeframe,” Conway said last week.
Since Mars Pathfinder, NASA’s explorers at the red planet have been on the hunt for water, not life.
NASA’s Spirit and Opportunity rovers launched in 2003 and found evidence of ancient hot springs and a coastline with the discovery of fine-grained silica soil and layered rock patterns, environments that could support hardy microorganisms known to live on Earth. Opportunity also returned data suggesting water on Mars may have been drinkable, before an acidic period in the planet’s ancient past, according to mission scientists.
NASA’s Phoenix lander arrived at Mars in May 2008, descending to Mars’ arctic plains for a five-month mission that scooped up the uppermost layer of soil to find ice deposits lying just inches deep. Phoenix also detected light snowfall from high-altitude cirrus clouds, adding to scientists’ understanding of the Martian water cycle.
Phoenix discovered perchlorate, an unexpected chemical in Martian soil that is toxic to some Earth-based life forms and serves as food for others. Perchlorate also has implications for future human expeditions to Mars because it can be refined into rocket fuel.
The Curiosity rover has traversed across Gale Crater since August 2012, and measurements collected at multiple stops near the mission’s landing site led scientists to surmise the 96-mile (154-kilometer) impact basin once had flowing rivers and a large lake, or system of lakes.
One of the most eye-catching discoveries in recent years comes from aerial imagery taken by a high-resolution camera aboard NASA’s Mars Reconnaissance Orbiter. Scientists analyzing the images, and spectral data to go with it, found intermittent seasonal briny water flows on steep hillsides and crater walls, an environment that could be ripe for microbial life today.
The flows could be triggered by the warmth of the sun causing shallow ice to melt and flow down the slopes, or the recurring features, which appear as dark streaks to MRO’s camera, could stem from water bubbling up from shallow aquifers.
“That means we have the potential to access that subsurface water on Mars quite easily,” Stofan said. “So, again, it goes back to this question (of life). If there’s life on Mars, that’s probably the environment in which we would find it potentially in the future, so these are extremely exciting sites for potential future exploration.”
But finding a recognizable organism near one of the water flows will be difficult. NASA has designated the flow sites as “special regions” that should be avoided by humans or any spacecraft not sterilized with extreme care, and many scientists don’t agree on what a new space instrument designed to find life should measure.
One dream scenario proposed by NASA officials planning human missions to Mars might involve an astronaut base in orbit around the planet, or on the surface miles away from the sensitive water flows. In such a case, crew members could direct ultra-clean rovers via real-time remote control radio links to explore for life without putting astronauts, or the potential alien microbes, in jeopardy from contamination.
Rover drivers on Earth can only send the Curiosity and Opportunity craft pre-programmed commands due to the minutes-long communications lag. At closer distances, astronauts could drive rover scouts as they would fly a drone or play a video game.
Two rovers set for launch in 2020 will come closer to resolving the Martian life quandary than any mission since the Viking landers.
Europe’s ExoMars rover has a drill to bore up to 6 feet (2 meters) into the Martian crust and pull out core samples. Due to arrive at Mars in early 2021, the craft will dump the material into an on-board mini-laboratory jointly developed by U.S. and European scientists charged with sniffing out low concentrations of organics, then determining whether the molecules are from extinct or extant life.
It’s a big question, and one that hasn’t been directly posed by a Mars mission since Viking.
The ExoMars rover’s focus is on underground samples, where any existing life or remains of extinct organisms could be better preserved, shielded from ionizing radiation at the planet’s surface.
An immobile science station going to the red planet with the ExoMars rover in 2020 may also be able to conduct a follow-up Labeled Release measurement similar to the Viking experiment, Levin said. The jury is still out on whether that objective will be part of the ExoMars flight plan, he said.
The ExoMars rover will be systematically cleansed before its launch, and it will be the first interplanetary probe sterilized to the same life-seeking standard as the Viking landers.
NASA’s next Mars rover is also set for launch in 2020, and part of its mission is to gather and tag rock and soil samples for retrieval by another mission later in the 2020s. Future spacecraft will recover the specimens and return to them to Earth, or perhaps to a human-tended lab near Earth, for inspection.
“This is a very important mission,” said Jim Green, director of NASA’s planetary science division. “It actually, in many ways, is a follow-up to the Vikings.
“It enables us to bring the right environment back, put it in our laboratories to study Mars, and resolve the question of whether there is life on Mars or not,” Green said. “In addition to the rock samples, we’ll also have regolith and soil samples. We’ll be able to perform the Labeled Release experiment in our own laboratories, and understand really what the physics is behind the observations that were made by the Labeled Release experiment while it sat on Mars and performed its job (on Viking 1 and 2).”
Nevertheless, Levin still stands by the initial results from the Labeled Release investigation on the Viking landers.
A group of biologists in 2012 took another look at the Viking data, plugged the measurements into a numerical model, and determined the experiment likely scooped up respirating microbes. The team was led by Joseph Miller, a neurobiologist at the University of Southern California, who previously led a study that found the gas output from the Viking Labeled Release samples fluctuated on cycles of nearly 24.7 hours, roughly the duration of a Martian day.
Miller said that could be an indication of a circadian rhythm, the day-night cycle observed in most living things.
“In addition to the 55,000 pictures of the surface of Mars taken from orbit, in addition to the 5,500 pictures of the Mars surface (from the landers), in addition to the first measurements of atmospheric composition, pressure and density,” Levine said in a NASA science meeting last year, “in addition to the discovery that the surface of Mars is unlike any other surface in the solar system, it just may be that in 1976 the people sitting in this room actually discovered the presence of life on the surface of Mars.”
Speaking at last week’s anniversary gathering in Hampton, Virginia, Levin harkened back to his early career as a municipal wastewater expert and offered this advice to future Mars colonists: “When you do get to Mars, do not drink the water.”
Email the author.
Follow Stephen Clark on Twitter: @StephenClark1. | 0.895868 | 3.431532 |
Studying the elements present in our solar system allow researchers to make certain conclusions about its origins.
Daniela Carollo, an Italian astronomer working at Australia’s Macquarie University, sheds some light on carbon-enhanced / metal-poor or CEMP stars.
Dr. Daniela Carollo is a research astronomer at Macquarie University in Sydney, Australia. She born in Italy where she received her M.D. in astrophysics from the University of Turin and earned her spot as research scientist at the Italian National Institute for Astrophysics in Turin (INAF). After six years as researcher there, Dr. Carollo decided it was time for a change of scenery and moved initially to Michigan State University for a visiting scholar and then to Australia to pursue a PhD program in Astronomy & Astrophysics at the Australian National University. She received her Ph.D in 2011 and she was offered the Australian Research Council – Super Science Fellowship at Macquarie University the same year. In 2010 she received the prestigious Humboldt Award in Germany, granted to exceptionally qualified scientists and scholars on all the disciplines. Dr Carollo is author of numerous high impact papers, including a Nature article on the duality of the galactic halo (2007). She is also an accomplished visual artist as she has performed several exhibitions in different location in the world.
Daniela Carollo – A Star is Born
The oldest stars of the Milky Way reside in the halo system, a very extended stellar population that comprises two main components: the inner and the outer halo. Both components contain carbon-enhanced metal-poor or CEMP stars.
Compared to our sun, these stars are characterized by low metal and high carbon content in their atmosphere.
We further observed that the outer halo contains a greater number of CEMP stars with low levels of elements heavier than iron, named CEMP-no. In contrast, the inner halo contain high quantities of CEMP stars that are also enhanced in elements heavier than iron, named CEMP-s.
This difference in the chemical signature is fundamental.
Around 400 million years after the Big Bang, the first stars appeared made mainly of hydrogen and helium.
This pristine population has never been observed, but they left their chemical signature in the next generation of stars. We believe that this signature is carried by the CEMP-no class of stars, and indeed, almost all the most metal deficient stars in the Milky Way belong to this category.
CEMP-no and CEMP-s stars had different ancestors. In the case of CEMP-no stars, it was the explosion of massive first stars. The CEMP-s stellar progenitors were intermediate-mass stars with a low mass companion with which it underwent mass transfer.
The discovery suggests the primordial gas clouds that formed the inner halo of the Galaxy were massive and crowded with stars two to three times the mass of the Earth’s sun, while the gas clouds that formed the outer halo were smaller and containing one or few stars that lived a few million years before exploding and producing the distinctive pattern of heavier metals.
This pattern appears in most of the ultra metal poor stars, including the recently discovered oldest star in the galaxy, which is 13.6 billion years old | 0.847767 | 3.755483 |
The main story is at the Space Daily and it about the impact of solar changes on communications satellites, spacecraft, and high altitude flyers. However, this latest research on reduced solar activity could have a major impact our climate. First the research and then the climate impact.
Recent research shows that the space age has coincided with a period of unusually high solar activity, called a grand maximum. Isotopes in ice sheets and tree rings tell us that this grand solar maximum is one of 24 during the last 9,300 years and suggest the high levels of solar magnetic field seen over the space age will reduce in future.
Graduate student Luke Barnard of the University of Reading will present new results on ‘solar climate change’ in his paper at the National Astronomy Meeting in Manchester.
The level of radiation in the space environment is of great interest to scientists and engineers as it poses various threats to man-made systems including damage to electronics on satellites. It can also be a health hazard to astronauts and to a lesser extent the crew of high-altitude aircraft.
The main sources of radiation are galactic cosmic rays (GCRs), which are a continuous flow of highly energetic particles from outside our solar system and solar energetic particles (SEPs), which are accelerated to high energies in short bursts by explosive events on the Sun.
The amount of radiation in the near-Earth environment from these two sources is partly controlled in a complicated way by the strength of the Sun’s magnetic field.
There are theoretical predictions supported by observational evidence that a decline in the average strength of the Sun’s magnetic field would lead to an increase in the amount of GCRs reaching near-Earth space.
By comparing this grand maximum with 24 previous examples, Mr. Barnard predicts that there is an 8% chance that solar activity will fall to the very low levels seen in the so-called ‘Maunder minimum’, a period during the seventeenth century when very few sunspots were seen.
Livingston and Penn have been observing the strength of the magnetic fields on the sun, especially around sunspots and have predicted that by Cycle 25 the sunspots will vanish, resulting in another grand minimum.
According to Henrik Svensmark’s cosmic theory of climate change, which was validated in experiments in 2006 and then reconfirmed in 2011 in the CLOUD experiment at CERN, cosmic rays coming from old supernovas can indeed make molecular clusters that can grow nearly a million times in mass to be large enough to become “cloud condensation nuclei” on which water droplets can form. Just a 10% increase in cloud cover from significantly reduce the earths temperature, and could bringing on a little ice age.
Readers can learn more about cosmic rays and climate change in The Chilling Stars: A New Theory of Climate Change by Nigel Calder and Henrik Svensmark.
If Luke Barnard’s solar climate change research is correct, a quiet sun will allow more cosmic ray reach the earth. And, if Henrik Svensmark is correct then these cosmic rays will produce more clouds , and we can expect a much cooler world.
The question is will be have another little ice age? You thoughts are most welcome in the comments. | 0.839032 | 3.863425 |
The most important result was the unique composition of the new stars. They consist mostly of neon and oxygen, with no trace of hydrogen and helium, which are the dominant constituents of normal stars like the Sun.
How is this possible? Did FAU astronomers detect zombie-dwarfs, survivors of a supernova? Previous numerical simulations suggested that such an explosion would destroy the white dwarf completely. The former companion would be left behind and then ejected from the Milky Way at hyper-speed. New models, however, revealed that in specific conditions the white dwarf is not destroyed entirely. However, it remained unclear why these relics of a stellar death contain no carbon, which they should have according to the numerical models.
How is the white dwarf relic ejected — and what happens to the companion star? The researchers came up with a plausible explanation.http://4840.ru/components/handy/mohoq-spionage-software-kostenlos.php
One of the Milky Way’s fastest stars is an invader from another galaxy | Science | AAAS
The stellar companion had to be very close to the white dwarf for mass to be transferred to the latter, causing an explosion. This means both stars would be required to orbit their common centre of mass at extreme velocities. When the white dwarf exploded, it received a kick so strong that it broke the link between the binary stars, causing both partners to fly out in different directions at hyper-speed. The team has successfully discovered a new class of HVSs as well as identifying a new physical slingshot mechanism for HVSs.
The results have been accepted for publication in the renowned scientific journal Monthly Notices of the Royal Astronomical Society. The journal Nature has reported the paper as a research highlight.
Ulrich Heber Tel. For example, how bright the X-rays are, how they change over time, and how they are distributed across the range of energy that Chandra observes. In this case, the data suggest that the point-like source is one component of a binary star system. In such a celestial pair, either a neutron star or black hole formed when the star went supernova is in orbit with a star much larger than our Sun. As they orbit one another, the dense neutron star or black hole pulls material away its companion star through the wind of particles that flows away from its surface.
If this result is confirmed, DEM L would be only the third binary containing both a massive star and a neutron star or black hole ever found in the aftermath of a supernova. Chandra's X-ray data also show that the inside of the supernova remnant is enriched in oxygen, neon and magnesium. This enrichment and the presence of the massive star imply that the star that exploded had a mass greater than 25 times, to perhaps up to 40 times, that of the Sun.
One of the Milky Way’s fastest stars is an invader from another galaxy
Optical observations with the South African Astronomical Observatory's 1. A detailed measurement of the velocity variation of the massive companion star should provide a definitive test of whether or not the binary contains a black hole. Indirect evidence already exists that other supernova remnants were formed by the collapse of a star to form a black hole.
However, if the collapsed star in DEM L turns out to be a black hole, it would provide the strongest evidence yet for such a catastrophic event.
What does the future hold for this system? If the latest thinking is correct, the surviving massive star will be destroyed in a supernova explosion some millions of years from now. When it does, it may form a binary system containing two neutron stars or a neutron star and a black hole, or even a system with two black holes. A paper describing these results is available online and was published in the November 10, issue of The Astrophysical Journal.
Dickel and P. Edwards, M. Perry and R.
Hubble Snags First View of Supernova Explosion's Sole Survivor
I remember when Chandra first launched aboard shuttle, lots of PR over Cmdr. Thanks for allowing us to share in these magnificent discoveries. I am 15, and this is very interesting, I love space I think its so cool and adventurous and crazy how big our stars can be. A star cannot survive the supernova blast, being run out of fuel and energy, the blast is enough to bust it out. I am Marvin L. My question is what was it that this star was able to survive the blast from the Supernova? Marvin Lee Stacks. Images by Date. Image Use Policy. View Wavelengths Composite X-ray Optical.
Astronomers have found evidence for a companion star that survived the blast of a supernova explosion. Chandra's X-rays reveal a point-like source within the debris field produced when a massive star exploded. This system contains either a neutron star or black hole and a surviving massive star. Visitor Comments 5.
Posted by Don Lehner on Friday, Posted by Naman on Sunday, This was exciting to read and view. Thank you. Michael Peoni Posted by michael peoni on Friday, | 0.837476 | 3.95296 |
Moon* ♍ Virgo
Moon phase on 8 September 2094 Wednesday is Waning Crescent, 28 days old Moon is in Virgo.Share this page: twitter facebook linkedin
Previous main lunar phase is the Last Quarter before 6 days on 1 September 2094 at 18:09.
Moon rises after midnight to early morning and sets in the afternoon. It is visible in the early morning low to the east.
Moon is passing first ∠2° of ♍ Virgo tropical zodiac sector.
Lunar disc appears visually 7.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1768" and ∠1905".
Next Full Moon is the Harvest Moon of September 2094 after 15 days on 24 September 2094 at 08:33.
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 28 days old. Earth's natural satellite is moving from the second to the final part of current synodic month. This is lunation 1170 of Meeus index or 2123 from Brown series.
Length of current 1170 lunation is 29 days, 15 hours and 55 minutes. It is 18 minutes shorter than next lunation 1171 length.
Length of current synodic month is 3 hours and 11 minutes longer than the mean length of synodic month, but it is still 3 hours and 52 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠167.4°. At the beginning of next synodic month true anomaly will be ∠190.4°. 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°).
Moon is reaching point of apogee on this date at 16:37, this is 13 days after last perigee on 26 August 2094 at 01:39 in ♓ Pisces. Lunar orbit is starting to get closer, while the Moon is moving inward the Earth for 14 days ahead, until it will get to the point of next perigee on 23 September 2094 at 11:57 in ♓ Pisces.
This apogee Moon is 406 544 km (252 615 mi) away from Earth. It is 1 136 km farther than the mean apogee distance, but it is still 165 km closer than the farthest apogee of 21st century.
4 days after its ascending node on 3 September 2094 at 19:00 in ♊ Gemini, the Moon is following the northern part of its orbit for the next 9 days, until it will cross the ecliptic from North to South in descending node on 18 September 2094 at 08:20 in ♑ Capricorn.
4 days after beginning of current draconic month in ♊ Gemini, the Moon is moving from the beginning to the first part of it.
4 days after previous North standstill on 4 September 2094 at 07:14 in ♋ Cancer, when Moon has reached northern declination of ∠23.478°. Next 10 days the lunar orbit moves southward to face South declination of ∠-23.617° in the next southern standstill on 18 September 2094 at 21:55 in ♑ Capricorn.
After 1 day on 9 September 2094 at 20:31 in ♍ Virgo, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.128027 |
Researchers announced the discovery of a black hole, shown in the above illustration, that grew much more quickly than its host galaxy, in July 2015. The discovery calls into question previous assumptions on the development of galaxies. The black hole was originally discovered using NASA’s Hubble Space Telescope, and was then detected in the Sloan Digital Sky Survey and by ESA’s XMM-Newton and NASA’s Chandra X-ray Observatory.
Benny Trakhtenbrot, from ETH Zurich’s Institute for Astronomy, and an international team of astrophysicists, performed a follow-up observation of this black hole using the 10 meter Keck telescope in Hawaii and were surprised by the results. The data, collected with a new instrument, revealed a giant black hole in an otherwise normal, distant galaxy, called CID-947.
Illustration Credit: M. Helfenbein, Yale University / OPAC
source Chandra X-Ray Observatory | 0.816734 | 3.432396 |
Against all Odds: Astronomers Baffled by Discovery of Rare Quasar Quartet
May 14, 2015
|Background information||Questions & Answers||Image download|
Hitting the jackpot is one thing, but if you hit the jackpot four times in a row you might wonder if the odds were somehow stacked in your favor. A group of astronomers led by Joseph Hennawi of the Max Planck Institute for Astronomy have found themselves in exactly this situation. They discovered the first known quasar quartet: four quasars, each one a rare object in its own right, in close physical proximity to each other.
Quasars constitute a brief phase of galaxy evolution, powered by the infall of matter onto a supermassive black hole at the center of a galaxy. During this phase, they are the most luminous objects in the Universe, shining hundreds of times brighter than their host galaxies, which themselves contain hundreds of billions of stars. But these hyper-luminous episodes last only a tiny fraction of a galaxy’s lifetime, which is why astronomers need to be very lucky to catch any given galaxy in the act. As a result, quasars are exceedingly rare on the sky, and are typically separated by hundreds of millions of light years from one another. The researchers estimate that the odds of discovering a quadruple quasar by chance is one in ten million. How on Earth did they get so lucky?
Clues come from peculiar properties of the quartet’s environment. The four quasars are surrounded by a rare giant nebula of cool dense hydrogen gas - which the astronomers dubbed the "Jackpot nebula", given their surprise at discovering it around the already unprecedented quadruple quasar. The nebula emits light because it is irradiated by the intense glare of the quasars. In addition, both the quartet and the surrounding nebula reside in a rare corner of the universe with a surprisingly large amount of matter. “There are several hundred times more galaxies in this region than you would expect to see at these distances” explains J. Xavier Prochaska, professor at the University of California Santa Cruz and the principal investigator of the Keck observations.
Given the exceptionally large number of galaxies, this system resembles the massive agglomerations of galaxies, known as galaxy clusters, that astronomers observe in the present-day universe. But because the light from this cosmic metropolis has been travelling for 10 billion years before reaching Earth, the images show the region as it was 10 billion years ago, less than 4 billion years after the big bang. It is thus an example of a progenitor or ancestor of a present-day galaxy cluster, or proto-cluster for short.
Piecing all of these anomalies together, the researchers tried to understand what appears to be their incredible stroke of luck. Hennawi explains “if you discover something which, according to current scientific wisdom, should be extremely improbable, you can come to one of two conclusions: either you just got very lucky, or you need to modify your theory.”
The researchers speculate that some physical process might make quasar activity much more likely in specific environments. One possibility is that quasar episodes are triggered when galaxies collide or merge, because these violent interactions efficiently funnel gas onto the central black hole. Such encounters are much more likely to occur in a dense proto-cluster filled with galaxies, just as one is more likely to encounter traffic when driving through a big city.
"The giant emission nebula is an important piece of the puzzle," says Fabrizio Arrigoni-Battaia, a PhD student at the Max Planck Institute for Astronomy who was involved in the discovery, “since it signifies a tremendous amount of dense cool gas.” Supermassive black holes can only shine as quasars if there is gas for them to swallow, and an environment that is gas rich could provide favorable conditions for fueling quasars.
On the other hand, given the current understanding of how massive structures in the universe form, the presence of the giant nebula in the proto-cluster is totally unexpected. According to Sebastiano Cantalupo of ETH Zurich, a co-author of the study: "Our current models of cosmic structure formation based on supercomputer simulations predict that massive objects in the early universe should be filled with rarefied gas that is about ten million degrees, whereas this giant nebula requires gas thousands of times denser and colder."
"Extremely rare events have the power to overturn long-standing theories," says Hennawi. As such, the discovery of the first quadruple quasar may force cosmologists to rethink their models of quasar evolution and the formation of the most massive structures in the universe.
The results described here will be published as Hennawi et al., "Quasar Quartet Embedded in Giant Nebulae Reveals Rare Massive Structure in Distant Universe" in the May 15, 2015 edition of the journal Science.
More information, including a copy of the paper, can be found online at the Science press package at http://www.eurekalert.org/jrnls/sci. You will need your EurekAlert user ID and password to access this information.
The members of the group are Joseph F. Hennawi (Max Planck Institute for Astronomy), J. Xavier Prochaska (University of California at Santa Cruz), Sebastiano Cantalupo (University of California at Santa Cruz; ETH Zurich) and Fabrizio Arrigoni-Battaia (Max Planck Institute for Astronomy).
The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.
The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
What is new / unusual / interesting about the discovery?
First, the extremely low probability of a discovery like this occurring by chance. Even close pairs of quasars are very rare: Out of the nearly 500,000 quasars that astronomers have cataloged to date, only about a hundred such binary quasars are known. It came as a big surprise in 2007, when a team of American and Swiss astronomers announced the discovery of the first triple quasar. But now the newly discovered quadruple quasar by Hennawi and collaborators (cf. “How was the quadruple quasar discovered?”, below) dramatically ups the ante, since the probability of finding such an object by chance is estimated to be one in ten million.
Such extremely low odds forced the scientists to consider that they are perhaps not dealing with an incredibly unlikely chance discovery, but rather that some physical process makes quasars much more likely to occur in specific environments, making the odds more favorable. This is where the unusual combination of properties for this region of space comes into play. The quasar quartet is embedded in an exceptionally bright and large emission nebula, and at the same time, resides in a massive proto-cluster of galaxies (as mentioned in the main text, our images show this region at a time when the universe was less than a third its current age).
This combination could be the key to explaining why the unusual quadruple quasar was discovered – it may be that quasar episodes are more likely to be triggered in such an unusual environment, which is rich in both gas and galaxies, as the researchers speculate. But the combination also poses new questions: Given our current understanding of the formation of such massive structures, giant emission nebulae and proto-clusters are not expected to occupy the same regions of space.
What are quasars, and why are they so rare?
Quasars constitute a brief phase of galaxy evolution, powered by the infall of matter onto a supermassive black hole at the center of a galaxy. During this phase, they are the most luminous objects in the Universe, shining hundreds of times brighter than their host galaxies, which themselves contain up to hundreds of billions of stars. Astronomers believe that every galaxy has a supermassive black hole embedded in its center, with typical masses between a few million and a few billion times the mass of our Sun. As matter swirls around these supermassive black holes, it travels at velocities near the speed of light, and is heated to temperatures of a million degrees, emitting copious amounts of light before being inevitably swallowed by the black hole.
The peak of quasar activity in galaxies occurred when the Universe was about one fifth of its current age, whereas today all massive galaxies are observed to have supermassive black holes at their centers that are dormant, which is to say that there is no significant inflow of matter onto them. However, in order to reach their present masses, these black holes must have swallowed enormous amounts of matter in the past, and current models link this growth to the galaxies' quasar episodes. The physical processes that determine when and why supermassive black holes shine as quasars are poorly understood, but it probably has to do with the supply of fuel: in order to ignite a quasar, a large amount of gas must find its way deep into the core of a galaxy, sufficiently close to experience the gravitational pull of the black hole.
While all supermassive black holes in massive galaxies underwent a quasar phase at some point in their evolution, this phase lasts only around ten million years, a thousand times shorter than the much longer ages of galaxies (about ten billion years and counting). Thus when we observe a quasar, we are catching a galaxy during a very brief period in its life, which explains why quasars are so rare on the sky, and hence typically separated by hundreds of millions of light years from one another.
How was the quadruple quasar discovered?
Hennawi and his colleagues were searching for quasars surrounded by so-called Lyman-α (pronounced “Lyman-alpha”) nebulae. If a quasar is surrounded by a large reservoir of cool hydrogen gas, the intense radiation emitted by the quasar can act like a ‘cosmic flashlight’, illuminating gas in its neighborhood and thereby revealing its structure. Under the quasar flashlight’s intense glare, the hydrogen gas emits light via the same mechanism at work in an ordinary fluorescent lamp, namely because it is being constantly bombarded with energy. In the case of ordinary lamps this energy is provided by an electrical current, whereas in Lyman-α nebulae the fluorescence is powered by energy from the quasar radiation (cf. MPIA Science Release 1/2014).
In their search for new Lyman-α nebulae, the researchers visually examined the spectra of 29 quasars to look for signatures of diffuse extended emission characteristic of fluorescing gas. One of their candidates, with the catalogue number SDSSJ0841+3921, appeared promising, and was then subjected to detailed observations using the LRIS imaging spectrometer at the 10m Keck Telescope on the summit of Maunakea in Hawaii. The object was observed with Keck/LRIS for 3 hours in late 2012, using a custom-built narrow-band filter that was tuned to capture only the light emitted by cool hydrogen gas (i.e. using a Lyman-α filter customized for the objects particular redshift).
These observations revealed one of the largest and brightest Lyman-α nebulae known to astronomy. The object is so distant that its light has taken nearly 10.5 billion years to reach us (cosmological redshift z = 2.041). The nebula has an extent of one million light-years across (310 kpc, corresponding to an angular size of 37 arcseconds). In the process of examining these images, the astronomers realized that there was not just one quasar, but four of them embedded in the nebula in one large physical structure. Examination of the four quasar spectra confirmed that these were indeed four distinct quasars (rather than multiple images of a single quasar; a phenomenon that can occur through gravitational lensing, when light is bent by the gravity of a massive object in the foreground). After their surprising find, the astronomers began referring to the giant Lyman-α nebula as the "Jackpot nebula".
What is a proto-cluster?
The largest gravitationally bound structures in the present-day universe are not individual galaxies, but rather huge agglomerations of up to a thousand galaxies, known as galaxy clusters, which extend several millions of light years across. In our current picture of structure formation, a cluster of galaxies continuously grows over cosmic time as more matter and galaxies collapse onto it due to its attractive gravitational force. Proto-cluster is the name given to the ancient progenitors of present-day clusters. Astronomers can directly observe such proto-clusters if they look sufficiently far into the distance - after all, in astronomy, the further you look into space, the further you look into the past.
For example, the light from the proto-cluster discovered around the quadruple quasar took 10.5 billion years to reach Earth (cosmological redshift z =2.041), and thus provides a view of what clusters of galaxies looked like just 4 billion years after the big bang. The proto-cluster has a size of several hundred thousand-light years, and within this region there are hundreds of times more galaxies than expected at a typical location in the distant universe. | 0.88639 | 3.746404 |
New formation theory explains the mysterious interstellar object ‘Oumuamua
Article published by: sciencedaily.com
Since its discovery in 2017, an air of mystery has surrounded the first known interstellar object to visit our solar system, an elongated, cigar-shaped body named ‘Oumuamua (Hawaiian for “a messenger from afar arriving first”).
How was it formed, and where did it come from? A new study published April 13 in Nature Astronomy offers a first comprehensive answer to these questions.
First author Yun Zhang at the National Astronomical Observatories of the Chinese Academy of Sciences and coauthor Douglas N. C. Lin at the University of California, Santa Cruz, used computer simulations to show how objects like ‘Oumuamua can form under the influence of tidal forces like those felt by Earth’s oceans. Their formation theory explains all of ‘Oumuamua’s unusual characteristics.
“We showed that ‘Oumuamua-like interstellar objects can be produced through extensive tidal fragmentation during close encounters of their parent bodies with their host stars, and then ejected into interstellar space,” said Lin, professor emeritus of astronomy and astrophysics at UC Santa Cruz.
Discovered on October 19, 2017, by the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1) in Hawaii, ‘Oumuamua is absolutely nothing like anything else in our solar system, according to Zhang. Its dry surface, unusually elongated shape, and puzzling motion even drove some scientists to wonder if it was an alien probe.
“It is really a mysterious object, but some signs, like its colors and the absence of radio emission, point to ‘Oumuamua being a natural object,” Zhang said.
“Our objective is to come up with a comprehensive scenario, based on well understood physical principles, to piece together all the tantalizing clues,” Lin said.
Astronomers had expected that the first interstellar object they detected would be an icy body like a comet. Icy objects like those populating the Oort cloud, a reservoir of comets in the outermost reaches of our solar system, evolve at very large distances from their host stars, are rich in volatiles, and are often tossed out of their host systems by gravitational interactions. They are also highly visible due to the sublimation of volatile compounds, which creates a comet’s coma (or “tail”) when it is warmed by the sun. ‘Oumuamua’s dry appearance, however, is similar to rocky bodies like the solar system’s asteroids, indicating a different ejection scenario.
Other researchers have calculated that there must be an extremely large population of interstellar objects like ‘Oumuamua. “The discovery of ‘Oumuamua implies that the population of rocky interstellar objects is much larger than we previously thought,” Zhang said. “On average, each planetary system should eject in total about a hundred trillion objects like ‘Oumuamua. We need to construct a very common scenario to produce this kind of object.”
When a smaller body passes very close to a much bigger one, tidal forces of the larger body can tear the smaller one apart, as happened to comet Shoemaker-Levy 9 when it came close to Jupiter. The tidal disruption processes can eject some debris into interstellar space, which has been suggested as a possible origin for ‘Oumuamua. But whether such a process could explain ‘Oumuamua’s puzzling characteristics remained highly uncertain.
Zhang and Lin ran high-resolution computer simulations to model the structural dynamics of an object flying close by a star. They found that if the object comes close enough to the star, the star can tear it into extremely elongated fragments that are then ejected into the interstellar space.
“The elongated shape is more compelling when we considered the variation of material strength during the stellar encounter. The ratio of long axis to short axis can be even larger than ten to one,” Zhang said.
The researchers’ thermal modeling showed that the surface of fragments resulting from the disruption of the initial body would melt at a very short distance from the star and recondense at greater distances, thereby forming a cohesive crust that would ensure the structural stability of the elongated shape.
“Heat diffusion during the stellar tidal disruption process also consumes large amounts of volatiles, which not only explains ‘Oumuamua’s surface colors and the absence of visible coma, but also elucidates the inferred dryness of the interstellar population,” Zhang said. “Nevertheless, some high-sublimation-temperature volatiles buried under the surface, like water ice, can remain in a condensed form.”
Observations of ‘Oumuamua showed no cometary activity, and only water ice is a possible outgassing source to account for its non-gravitational motion. If ‘Oumuamua was produced and ejected by the scenario of Zhang and Lin, plenty of residual water ice could be activated during its passage through the solar system. The resulting outgassing would cause accelerations that match ‘Oumuamua’s comet-like trajectory.
“The tidal fragmentation scenario not only provides a way to form one single ‘Oumuamua, but also accounts for the vast population of asteroid-like interstellar objects,” Zhang said.
The researchers’ calculations demonstrate the efficiency of tidal forces in producing this kind of object. Possible progenitors, including long-period comets, debris disks, and even super-Earths, could be transformed into ‘Oumuamua-size pieces during stellar encounters.
This work supports estimates of a large population of ‘Oumuamua-like interstellar objects. Since these objects may pass through the domains of habitable zones, the possibility that they could transport matter capable of generating life (called panspermia) cannot be ruled out. “This is a very new field. These interstellar objects could provide critical clues about how planetary systems form and evolve,” Zhang said.
According to Lin, “‘Oumuamua is just the tip of the iceberg. We anticipate many more interstellar visitors with similar traits will be discovered by future observation with the forthcoming Vera C. Rubin Observatory.”
U.S. Naval Academy astronomer Matthew Knight, who is co-leader of the ‘Oumuamua International Space Science Institute team and was not involved in the new study, said this work “does a remarkable job of explaining a variety of unusual properties of ‘Oumuamua with a single, coherent model.”
“As future interstellar objects are discovered in coming years, it will be very interesting to see if any exhibit ‘Oumuamua-like properties. If so, it may indicate that the processes described in this study are widespread,” Knight said.
About Jaime Bonetti Zeller
Jaime Bonetti Zeller is an investment professional and entrepreneur with businesses in multiple industries. He is president of Servicios Consulares Eurodom, the local partner in the Caribbean region for VFS Global, a leader global outsourcing and technology services specialist for diplomatic missions and governments worldwide. Jaime Bonetti Zeller also started the company Sofratesa de Panama inc., an organization in the engineering services industry located in Panama City. | 0.893837 | 3.909969 |
There's a big expiration date looming ahead in astrophysicist Kirpal Nandra's mind. The current X-ray space telescopes in orbit will likely be at or near the end of their lifetimes by about 2020, so plans are underway to develop a successor to keep watch on deep space.
With NASA's budget in flux, Nandra — who is with the Max Planck Institute for Extraterrestrial Physics — said Europe needs to act quickly and independently to cover the expected gap in X-ray astronomy.
Nandra will know very soon whether that's possible. He's part of a team proposing the Advanced Telescope for High-Energy Astrophysics (Athena+) concept to launch in 2028. By the end of November, the European Space Agency (ESA) will decide what science theme the mission will address, although it will take another year to decide which mission will be used. [The X-ray Universe: Photos from NASA's Chandra Space Telescope]
Athena+, though a strong candidate, faces some tough competition, Nandra told SPACE.com. Since X-rays are only visible from space, this is the last chance to put something up there within the next couple of decades.
"If Athena doesn't go forward, we won't have any X-ray eyes out there looking at the hot parts of the universe, or the energetic parts of the universe, in the 2020s," Nandra said.
Lighter and more sensitive
Previously, Nandra's team came very close to an X-ray telescope concept, only to see it yanked away. The International X-ray Observatory was backed by ESA, NASA and the Japan Aerospace Exploration Agency before it was terminated in 2010. Budgetary problems within NASA caused it to pull back on IXO, Nandra said.
By contrast, Athena+ is solely European-funded and based partly on the XMM-Newton telescope in orbit right now. But there are big differences.
The design calls for silicon plates to reduce the weight of the telescope while making it bigger — allowing an Ariane 5 rocket (the biggest booster the Europeans have) to heft the 12-meter (39.4 feet) machine into orbit.
On board will be a new kind of detector — the X-Ray Integral Field Unit — that can detect a minute change in heat when a single X-ray photon is absorbed. Athena+ will also carry a wide-field imager (WFI), which can survey vast swatches of the universe at high sensitivity, but which is not limited to a narrow field of view.
"That combination is exactly what you need if you want to discover black holes growing in the deep universe, the earliest supermassive black holes," Nandra said, adding that another science goal is to understand how gas structures in the universe formed and evolved.
Ripples across the universe
With Athena+, researchers hope to learn how these giant black holes — which form in galaxies — affect the rest of the universe. They're plenty powerful: Nandra said scientists have seen these effects in collections of thousands of galaxies. In these clusters, the energy output of the black hole at the center can be seen bubbling and stirring up gas millions of light-years away.
The presence of a black hole can also stop star formation inside of a galaxy as it blows out the gas, Nandra said. "It turns an active star-forming galaxy into a passive galaxy, a process that we call cosmic feedback, and that's one of the things that we're trying to work out — how that process happens — with Athena."
Athena+ is expected to cost 1.2 billion to 1.3 billion euros ($1.6 billion to $1.8 billion), including launch costs. If it passes the competition, Athena+ will still need to meet several key design and construction milestones before launch.
ESA has accepted dozens of white papers for two launch opportunities in 2028 and 2034. Mission concepts include a planetary science infrared observatory, a mission to study Neptune and Triton, and an orbiter and lake probe for Saturn's moon Titan. | 0.882315 | 3.396166 |
Most people think of asteroids as scary, cold, and lifeless blobs of rock hurtling around the solar system. That’s a pretty accurate description, but that doesn’t mean that asteroids don’t get to have families. According to a new study, 85% of all objects in the asteroid belt can trace their origin to five or six planetoids (small planets) that turned to smithereens in the early days of the solar system. Accordingly, there are five to six families of asteroids tracing their lineage back to these larger parent bodies.
About four to five billion years ago, the solar system was a chaotic, crowded mess. Many of today’s planets had yet to form in their current configuration and collisions between massive planetary bodies were quite routine. Eventually, all this colliding gave rise to many of the solar system’s moons and to the countless asteroids that litter the outskirts of the system. For instance, the main asteroid belt — located between the orbits of Mars and Jupiter — is estimated to contain millions of objects, although only hundreds of thousands have actually been observed.
While these parent bodies fragmented into thousands of smaller bits and pieces, it is possible to piece them back together based on their trajectories. In 1918, Japanese astronomer Kiyotsugu Hirayama was the first to notice that asteroids had similar elements, such as eccentricity and inclination, to their orbit. Suddenly, asteroids were no longer randomly zipping through the solar system but rather groups sharing orbital elements.
Based on Hirayama’s ideas, for the past 100 years, astronomers have grouped asteroids into families and non-families, with only half of all the asteroids that we know of being classed in families. However, this division into families and non-families is not productive, according to researchers led by Stanly Dermott, a Professor of Astronomy at the University of Florida.
Dermott and colleagues found that there’s a relationship between the orbital elements of asteroids and their sizes. By analyzing the dimensions of asteroids and their distribution within the inner asteroid belt, the team was able to classify 85% of the asteroid into about six families, each named after the biggest object in the family. They are Vesta, Flora, Nysa, Polana, Eulalia, and Hungaria. In 2011, NASA’s Dawn spacecraft visited Vesta.
The other 15 percent may also trace their origins to the same group of primordial bodies. What astronomers had previously thought of as ‘non-family’ asteroids were likely part of one of the six families, as well — just that they had become estranged due to the gravitational pull of Jupiter or Saturn, which changed their orbits ever so slightly.
The team only analyzed 200,000 asteroids, all found in the inner asteroid belt, which is closer to Earth and more studied than the middle or outer asteroid belt. A NASA survey tracked over 780,000 asteroids in the belt as a whole. This means there’s a lot of room to learn about asteroids. Perhaps there are more families, for instance. What’s more, there’s a similar ongoing analysis, only this time of meteorites, which are the bits of asteroids that survive atmospheric entry and reach Earth. This kind of information could prove essential to protecting the Earth and ourselves from killer asteroids of the kind that wiped out the dinosaurs.
“These large bodies whiz by the Earth, so of course we’re very concerned about how many of these there are and what types of material are in them,” Dermott said. “If ever one of these comes towards the Earth, and we want to deflect it, we need to know what its nature is.”
Scientific reference: The common origin of family and non-family asteroids, Nature Astronomy (2018). DOI: 10.1038/s41550-018-0482-4. | 0.904039 | 3.943194 |
Troubleshooting Titan: bubbles, submarines and cryogenic seas
Case Western Reserve and NASA Glenn scientists aim to keep effervescence from obstructing scientific equipment on spacecraft in frigid seas of Saturn’s largest moon
If scientists someday send a spacecraft to the surface of Titan, the largest moon orbiting Saturn, it could very well be a small autonomous submarine capable of navigating the frigid, liquefied natural gas seas found on the planet-sized moon.
And if the craft, the size of a smart car, succeeds in collecting vital physical and chemical details about those noxious seas and the smoggy skies overhead, it will be in part because a team at Case Western Reserve University and NASA Glenn Research Center in Cleveland first helped identify and overcome one small, but critical problem in that pioneering aquatic space mission: bubbles.
“You would hate to get a multi-million dollar spacecraft all the way there and successfully into the liquid methane, but then not be able to get any readings just because effervescence got in the way,” said Ramaswamy “Bala” Balasubramaniam, a research associate professor of mechanical and aerospace engineering at the Case School of Engineering. “There’s also a chance that the bubbles could impede the propellers, so it’s a real design concern.”
The problem stated more scientifically: “Because nitrogen gas (the chief gas of the Titan atmosphere) has a relatively high solubility in the liquid ethane and methane seas, waste heat generated by the submarine power system may cause dissolved nitrogen gas to come out of solution…” In other words, the hot engines of a submersible could generate troublesome bubbles that impede its mission.
The seas of Titan are primarily composed of liquid methane, liquid ethane and nitrogen at a surface temperature between 90 and 96 Kelvin (about minus 300 Fahrenheit.) The atmosphere is gaseous nitrogen (95%) and gaseous methane (5%).
A relatively low gravity—about one-sixth that of Earth—further complicates the matter, Balasubramaniam said. “On Earth, if you pour open a can of soda, all of the bubbles rise in the liquid, but in microgravity that doesn’t happen—they float around everywhere,” he said. “They could disrupt the mission completely.”The sub model used by researches to record effervescence.
Balasubramaniam and a pair of recent Case Western Reserve graduates, Jason Hartwig (2014) and Peter Meyerhofer (2019), worked on testing that design issue while the two were still graduate students at the engineering school. Their conclusion: Limits on the power system and increased insulation may be required to avoid excess effervescence, and for a submersible to successfully explore Titan’s seas.
Their research, with collaborators from the University of Texas-El Paso, Johns Hopkins Applied Physics Laboratory and Penn State Applied Research Lab, was published in the journal Planetary and Space Science.
Scientists had long speculated about the existence of hydrocarbon lakes and seas on Titan, and earlier space missions (the Cassini spacecraft in 2004, also with help from NASA Glenn) revealed that more than 620,000 square miles of Titan—almost 2% of its surface—are covered in liquid.
“This was an amazing discovery, and we’ve been thinking about it ever since,” Hartwig said. “This is the only place in the solar system that we know of other than Earth with stable, accessible liquid, and in our search for life in space, this is important.”
So NASA has long been planning to send a craft 886 million miles to Titan in 2025, and while the agency also is planning drone investigations of the moon, there has been increasing interest in plunging a submarine into the noxious northern lakes of Titan.
Because Titan also has the equivalent of hydrological cycle—but with methane and ethane, not H2O—there is a geological reason to visit the big moon, said Hartwig, who is now employed at NASA Glenn.
“Clouds form, and what amounts to liquid natural gas rain falls down, flows into rivers and these lakes—which are roughly the size of the Great Lakes—and then evaporates back into the clouds,” he said. “There’s a lot to study there.”
For more information, contact Mike Scott at [email protected].
(From The Daily, 1//8/2020) | 0.835069 | 3.53916 |
The enjoyment of astronomy could be lifelong or just a fad but so much is determined by how you’ve got your first experience. The two forms of astronomers rely upon each other – observers make observations with telescopes to check astronomical theories, or to try and understand unanswered questions. Astronomy majors on the undergraduate level will gain an introduction to this subject by taking a survey course that covers the Milky Way Galaxy, the orbital behaviors of planets, telescope basics, star identification and cosmology.
The Office of Astronomy for Growth (OAD) is a joint project of the International Astronomical Union (IAU) and the South African Nationwide Research Foundation (NRF) with the assist of the Division of Science and Expertise (DST). Astronomy is the branch of science that studies outer area focusing on celestial our bodies such as stars, comets, planets, and galaxies.
Our major source of details about celestial our bodies and different objects is visible mild , or more generally electromagnetic radiation 45 Observational astronomy may be categorized in line with the corresponding region of the electromagnetic spectrum on which the observations are made.
Those who you see in glossy science magazines are attributable to excessive degree telescopes that solely scientist and astronomer get entry to. The glowing stars that we see at evening are simply the tip and astronomy can provide many insights to our fabulous universe.
All the pieces to do with Astronomy: The novice hobby of man because the dawn of time and scientific study of celestial objects. The concepts of spacetime and gravity as a warping of spacetime are introduced together with observational proofs of his theories, together with the search for gravity waves with LIGO.
The traditional astronomers and monks, seen that the flooding all the time occurred at the summer solstice, which additionally just occurred to be when the intense star Sirius rose before the sun and so, they were capable of predict the annual flooding, a ability which in flip rendered them appreciable energy.
I discuss the techniques astronomers use to find out in regards to the planets, their atmospheres (what determines if an atmosphere sticks round; conduct of gases; what determines the surface temperature; ambiance layers; the transport of energy; effects of clouds, mountains, and oceans; climate vs. climate and local weather change agents with feedbacks; and appearance), their magnetic fields (the magnetic dynamo idea), and their interiors including the geological forces at work reshaping their surfaces. | 0.822096 | 3.078327 |
The June solstice – your signal to celebrate summer in the Northern Hemisphere and winter in the Southern Hemisphere – will happen on June 20, 2020, at 21:44 UTC. That’s 4:44 p.m. CDT in North America on June 20. Translate UTC to your time. For us in the Northern Hemisphere, this solstice marks the longest day of the year. Early dawns. Long days. Late sunsets. Short nights. The sun at its height each day, as it crosses the sky. Meanwhile, south of the equator, winter begins.
What is a solstice? Ancient cultures knew that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shifted in a regular way throughout the year.
They built monuments, such as Stonehenge, to follow the sun’s yearly progress.
Today, we know that the solstice is an astronomical event, caused by Earth’s tilt on its axis and its motion in orbit around the sun.
It’s because Earth doesn’t orbit upright. Instead, our world is tilted on its axis by 23 1/2 degrees. Earth’s Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly.
At the June solstice, Earth is positioned in its orbit so that our world’s North Pole is leaning most toward the sun. As seen from Earth, the sun is directly overhead at noon 23 1/2 degrees north of the equator, at an imaginary line encircling the globe known as the Tropic of Cancer – named after the constellation Cancer the Crab. This is as far north as the sun ever gets.
All locations north of the equator have days longer than 12 hours at the June solstice. Meanwhile, all locations south of the equator have days shorter than 12 hours.
When is the solstice where I live? The solstice takes place place on June 20, 2020, at 21:44 UTC. That’s 4:44 p.m. CDT in North America on June 20.
A solstice happens at the same instant for all of us, everywhere on Earth. To find the time of the solstice in your location, you have to translate to your time zone.
Here’s an example of how to do that. In the central United States, for those of us using Central Daylight Time, we subtract five hours from Universal Time. That’s how we get 16:44 (4:44 p.m.) CDT as the time of the 2020 June solstice (21:44 UTC on June 20 minus 5 equals 16:44 (4:44 p.m.) CDT on June 20.
Want to know the time in your location? Check out EarthSky’s article How to translate UTC to your time. And just remember: you’re translating from 21:44 UTC, June 20.
Where should I look to see signs of the solstice in nature? Everywhere. For all of Earth’s creatures, nothing is so fundamental as the length of the day. After all, the sun is the ultimate source of almost all light and warmth on Earth’s surface.
If you live in the Northern Hemisphere, you might notice the early dawns and late sunsets, and the high arc of the sun across the sky each day. You might see how high the sun appears in the sky at local noon. And be sure to look at your noontime shadow. Around the time of the solstice, it’s your shortest noontime shadow of the year.
If you’re a person who’s tuned in to the out-of-doors, you know the peaceful, comforting feeling that accompanies these signs and signals of the year’s longest day.
Is the solstice the first day of summer? No world body has designated an official day to start each new season, and different schools of thought or traditions define the seasons in different ways.
In meteorology, for example, summer begins on June 1. And every school child knows that summer starts when the last school bell of the year rings.
Yet June 21 is perhaps the most widely recognized day upon which summer begins in the Northern Hemisphere and upon which winter begins on the southern half of Earth’s globe. There’s nothing official about it, but it’s such a long-held tradition that we all recognize it to be so.
It has been universal among humans to treasure this time of warmth and light.
For us in the modern world, the solstice is a time to recall the reverence and understanding that early people had for the sky. Some 5,000 years ago, people placed huge stones in a circle on a broad plain in what’s now England and aligned them with the June solstice sunrise.
We may never comprehend the full significance of Stonehenge. But we do know that knowledge of this sort wasn’t limited to just one part of the world. Around the same time Stonehenge was being constructed in England, two great pyramids and then the Sphinx were built on Egyptian sands. If you stood at the Sphinx on the summer solstice and gazed toward the two pyramids, you’d see the sun set exactly between them.
How does it end up hotter later in the summer, if June has the longest day? People often ask:
If the June solstice brings the longest day, why do we experience the hottest weather in late July and August?
This effect is called the lag of the seasons. It’s the same reason it’s hotter in mid-afternoon than at noontime. Earth just takes a while to warm up after a long winter. Even in June, ice and snow still blanket the ground in some places. The sun has to melt the ice – and warm the oceans – and then we feel the most sweltering summer heat.
Ice and snow have been melting since spring began. Meltwater and rainwater have been percolating down through snow on tops of glaciers.
But the runoff from glaciers isn’t as great now as it’ll be in another month, even though sunlight is striking the northern hemisphere most directly around now.
So wait another month for the hottest weather. It’ll come when the days are already beginning to shorten again, as Earth continues to move in orbit around the sun, bringing us closer to another winter.
And so the cycle continues.
Bottom line: The 2020 June solstice happens on June 20 at 21:44 UTC. That’s 4:44 p.m. CDT in North America. This solstice – which marks the beginning of summer in the Northern Hemisphere – marks the sun’s most northerly point in Earth’s sky. It’s an event celebrated by people throughout the ages.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says. | 0.831053 | 3.296075 |
Crescent ♎ Libra
Moon phase on 2 December 2056 Saturday is Waning Crescent, 24 days old Moon is in Libra.Share this page: twitter facebook linkedin
Previous main lunar phase is the Last Quarter before 2 days on 30 November 2056 at 06:37.
Moon rises after midnight to early morning and sets in the afternoon. It is visible in the early morning low to the east.
Moon is passing about ∠9° of ♎ Libra tropical zodiac sector.
Lunar disc appears visually 0.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1937" and ∠1947".
Next Full Moon is the Cold Moon of December 2056 after 19 days on 22 December 2056 at 01:34.
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 24 days old. Earth's natural satellite is moving from the second to the final part of current synodic month. This is lunation 703 of Meeus index or 1656 from Brown series.
Length of current 703 lunation is 29 days, 10 hours and 10 minutes. It is 1 hour and 8 minutes shorter than next lunation 704 length.
Length of current synodic month is 2 hours and 34 minutes shorter than the mean length of synodic month, but it is still 3 hours and 35 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠353.9°. At beginning of next synodic month true anomaly will be ∠9.2°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
10 days after point of apogee on 21 November 2056 at 23:18 in ♉ Taurus. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 3 days, until it get to the point of next perigee on 6 December 2056 at 09:40 in ♐ Sagittarius.
Moon is 369 961 km (229 883 mi) away from Earth on this date. Moon moves closer next 3 days until perigee, when Earth-Moon distance will reach 357 324 km (222 031 mi).
6 days after its ascending node on 25 November 2056 at 19:20 in ♋ Cancer, the Moon is following the northern part of its orbit for the next 6 days, until it will cross the ecliptic from North to South in descending node on 8 December 2056 at 17:42 in ♑ Capricorn.
6 days after beginning of current draconic month in ♋ Cancer, the Moon is moving from the beginning to the first part of it.
6 days after previous North standstill on 25 November 2056 at 17:50 in ♋ Cancer, when Moon has reached northern declination of ∠22.815°. Next 6 days the lunar orbit moves southward to face South declination of ∠-22.839° in the next southern standstill on 8 December 2056 at 17:13 in ♑ Capricorn.
After 4 days on 6 December 2056 at 22:31 in ♐ Sagittarius, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.154839 |
International Space Station
Ever since mankind walked the Earth the sky has held a very special fascination. From the gentle light of the stars to the meandering paths of the planets we have grown to love and understand the night sky.
Over recent years though, there have been some strange interlopers in the night sky – man made satellites. One in particular seems to have captured the public imagination, the International Space Station (ISS).
As its name suggests, the station is the result of international collaboration between North America (NASA), Russia (RKA), Japan (JAXA), Europe (ESA) and Canada (CSA) and a combination of crew from those agencies operate the station.
It orbits the Earth at an average altitude of 369km and, travelling at 27,724km per hour, it takes about 90 minutes to complete one orbit.
In effect it’s in constant free-fall around the Earth, as it falls toward the Earth the curvature of the Earth's surface falls away from it.
The result is that it typically maintains a relatively constant altitude above the Earth's surface. However, because it orbits in the thermosphere, gas in the atmosphere creates a drag effect, very gently slowing the station. This causes it to descend into a lower orbit so a few times each year, it receives a boost to a higher altitude from either the onboard engines or from an attached spacecraft.
The first parts of the ISS were launched in 1998 and its first crew arrived in 2000 representing humankind’s permanent presence among the stars.
Even though it has been operational since 2000 its still not complete with more modules to add.
Completion is expected this year when the station will weigh around 400 tonnes and measure 51m by 109m (excluding the solar array which adds an additional 73m), making it four times larger than the Mir Space Station.
The space station is considered to be a 'third generation' station due to its modular design allowing for continual development or change to its structure, unlike the first generation stations which were of fixed design and configuration.
The first module in orbit was called Zarya and was launched aboard a Russian rocket. It was closely followed by a whole array of different functional sections from service modules to air locks and gymnasiums, as well as a 360 degree bay window, and of course no space station would be complete without a cargo bay or two.
There are now 15 modules which are pressurised (which astronauts can access without a cumbersome space suit) and a host of other unpressurised units.
One of the key unpressurised modules is the largest structure of all, the Integrated Truss Structure which connects up to the main solar arrays and station radiators. Measuring a whopping 108.5 m long its made up of 10 separate segments that form the backbone of the entire station.
There are also a number of other external devices attached to the station including six robotic arms, storage containers that carry spare parts and platforms for external experiments.
Living and working on the station is generally centered around the pressurised modules and for the comfort and hygiene of the crew there are areas designed for 'personal tasks'.
There are beds dotted around the station which seem nothing more advanced than sleeping bags strapped to the wall with a head strap to keep your head from floating around.
Eating is generally a group activity although the food is chosen by the astronauts (with assistance from dietary professionals) prior to joining the station. The foods are mostly refrigerated or canned and drinks often in powder form. The kitchen area has food heaters, a water supplier and a refrigerator. Its not uncommon for astronauts to choose spicy food with strong flavours because the taste sensation is reduced in space.
On the ISS the toilets have handles that enable the astronauts to hold position. A big fan with a suction hole is used to collect the waste product. Any solid waste is stored in sealed containers until the next visiting spacecraft arrives to bring it back to Earth for disposal. Urine is collected at the front of the toilet using a hose and an appropriately shaped male or female adaptor. Urine through the recycling systems onboard is reprocessed back to drinking water!
Over 200 astronauts have visited the station and it has been continually manned since October 2000 and for those astronauts onboard, they are taking some risk. The ISS is relatively protected from radiation in space, particularly from the Sun, as the Earth's magnetic field deflects radiation around it.
If particularly intense bursts of solar energy are detected then the crew will have just a few minutes warning to shelter in a more heavily shielded part of the station as happened last in 2005.
There is also the risk of meteoroid impact or space debris striking the station, and in 2011 and in March 2012 the crew sheltered in the escape module due to a proximity alert from passing debris.
One of the things that has inspired us about the space station is not only the international co-operation but the more humbling fact that on most days of the year, if you know where to look, you can look up and see the space station and its crew of intrepid human explorers pass overhead.
Its surprises many to know that you don't need any special equipment to see it as it's often brighter than any of the stars in the sky and very easy to pick out.
NASAs website has an ISS tracker which helps you to know where to look from your location.
If you become a fan of the ISS and look out for it regularly you will notice that, depending on your location, it will vanish from view for a period of time. This is explained by the complexities of the circumstances that give rise to it being visible and it's dependent on, amongst other things, whether it's actually above the horizon, whether it’s still being illuminated by the Sun, if the Sun has set and its altitude. There will be times when it's passing overhead but it's not lit up and therefore not visible. On occasions its altitude has to be boosted by either on board rockets or an attached visiting spacecraft.
The ISS is many things to many people but all would agree that it's a symbol of hope for future international cooperation. It’s an incredible technological achievement and not only does it help to capture the imagination of those on Earth's surface but it serves as a reminder that together, humans can achieve great things. | 0.848908 | 3.489836 |
Electric sail could send probe to explore Uranus
Sen—NASA’s New Horizons space probe is now just a year away from beginning its study of ex-planet Pluto, in the outer reaches of the Solar System. As the fastest probe ever fired into deep space, it has still taken many years to get there, having launched in January 2006 and racing to a speed of 55,500 km per hour.
It promises to be an exciting and revealing encounter, though one that is over in just a few months as New Horizons’ incredible speed sends it hurtling out into interstellar space. This space propulsion technique will not suit all remote voyages, and alternative technologies are being examined to reach the outer planets.
Among them is an interesting concept proposed by Finnish scientists which is a variation on the solar sail idea that is already being tested in space missions. The conventional sail is made of a thin fabric that catches photons in the solar wind much as a yacht’s sail is driven by the atmospheric winds.
The electric sail, or E-sail, being proposed by the Finnish team more resembles an umbrella’s pattern of spokes - wire tethers that when charged up will generate an electric field around the spacecraft and allow it to be pushed along by solar energy.
The concept of the E-sail was put together by engineer Pekka Janhunen, who is also leading a proposal to send a space probe to study the distant ice giant planet Uranus. And though it sounds like science fiction, a small Estonian satellite called ESTCube-1 is already testing the technique in orbit and ESA is also examining the concept.
Janhunen, of the Finnish Meteorological Institute, is Visiting Professor at Tartu University, Estonia, and believes probes powered like this could be used to visit several planets and moons in the outer Solar System.
He told Sen: “The E-sail can go on changing the vehicle’s course in the Solar System indefinitely without ever running out of fuel, and it can do so fast enough to be practically useful. It’s like an unlimited duration InterRail pass to the Solar System.”
An artist's image showing the ESTCube satellite in orbit. Credit: University of Tartu, ESTCube team
A full-sized sail, as shown in the main image, will consist of between 50 and 100 wires, each 20 km long but only a 25 or so microns in diameter, radiating away from the space probe. They will pack up into a tiny space for launch, but when unfurled they provide several square kilometres of wind-sail area. A solar-powered electron gun in the spacecraft will keep these tethers highly charged, so that they resemble a wall-like obstacle to the protons and alpha particles flowing in the solar wind.
Though the initial force of the wind pushing the spacecraft along will seem weak, the acceleration it provides means it could reach a speed of 30 km per second in a year, and the continued acceleration could send a small probe as far as Pluto in only five years.
For a larger probe, as envisioned for a mission to Uranus, nearly 3 billion km from Earth (1.8 billion km) the journey time is still estimated at about just six years at a speed of up to 72,000 km per hour. Changes in direction of the spacecraft can be applied by inclining the sail, or opening up gaps in it by killing the charge on certain tethers.
The main body of the space probe will still use some conventional rocket thrusters to allow for changes to the trajectory when it closes in on Uranus, which has an equatorial diameter of 50,700 km (31,500 miles). Once there, the team wants to send a probe into the planet’s atmosphere to tell us more about a world that still remains very much a mystery.
Janhunen’s team says an E-sail probe could study Uranus in a similar manner to how NASA’s Galileo measured Jupiter’s atmosphere in the 1990s and would help planetary scientists learn more about how the Solar System formed.
A video demonstrates how the Uranus probe will deploy its E-sail. Credit: Pekka Janhunen
Sen spoke to Chris Arridge, of University College London’s Mullard Space Science Laboratory in Surrey, who worked on plans for a mission called Uranus Pathfinder that ESA ultimately failed to back.
He said: “Travelling to the more distant reaches of our solar system will always take a relatively long time.
“This technology is at a very early stage of development and will require much more development for it to be used in a mission this far out in the Solar System. But if this can work we will be able to explore the Solar System much more cheaply and quickly.” | 0.826828 | 3.522184 |
Studying star and planet formation, circumstellar disks, and planetary system evolution and architecture.
Planet Formation and Evolution Research at STScI
Star and Planet Formation
Using dynamical and chemical models and multi-wavelength, ground-based, and space-based observations, STScI researchers have characterized the evolution of the physical and chemical properties of star and planet formation environments in single and multi-stellar systems. From stellar mass accretion and stellar jets and outflows, to the evolution of gas and dust in protoplanetary and transitional disks, these studies can shed light on the conditions for planet formation. Also of interest are the planet-disk interactions, triggering planet migration and affecting the dynamical evolution of the young planetary systems.
STScI researchers have used a wide range of models and multi-wavelength, ground-based, and space-based observations to characterize the physical and chemical properties of debris disks, including their evolution and spatial structure, and the planet-disk interactions. These studies, focused on detailed analyses of individual systems and statistical studies of large debris disk samples, can shed light on the planetesimal population that is responsible for the debris dust, helping constrain planetesimal and planet formation models and shedding light on the architecture of the extrasolar planetary systems.
Evolved Planetary Systems
The characterization of the planetesimal population around evolved stars has also been focus of investigation, via the study of the infrared excesses in white dwarfs and the study of the signatures of orbiting dust and gas revealed by transient or varying absorption features. These studies have also allowed the characterization of the elemental abundance of the disrupted, dust-producing planetesimals, shedding light on the bulk composition of the rocky exoplanets.
Star and Planet Formation Group at STScI
Group of STScI researchers that studies circumstellar gas and disk chemistry, accretion processes in protostellar disks and envelopes, the evolution of protostellar systems, episodic accretion, jets and outflows, and the interaction with molecular clouds, and star forming region populations.
Extrasolar Planetary Systems Imaging Group
The extrasolar planetary system imaging group is a group of staff, postdocs, and students at STScI, JHU, and other institutions that work collectively to image planetary systems and circumstellar disks.
The STScI Exoplanets, Star and Planet Formation Seminar Series
Weakly seminar series at STScI featuring visiting researchers on topics related to exoplanets, star and planet formation.
Planets, Life, and the Universe Lecture Series
The Planets, Life, and the Universe lecture series brings high-profile speakers to the JHU/STScI campus to discuss current topics of interest in astrobiology and draws a large and steadily increasing audience. The lectures are presented live online and are also available for viewing on the website afterwards.
Archival Legacy Investigations of Circumstellar Environments (ALICE)
The HST NICMOS coronagraphic archive is a valuable database for exoplanets and disks studies containing observations of about 400 targets that were obtained as part of surveys looking for substellar companions or resolved circumstellar disks to young nearby stars. The ALICE program is an HST Legacy program that has reevaluated the NICMOS coronagraphic archive with improved detection limits, achieved with modern post-processing methods. The ALICE team has published high-level science products of NICMOS coronagraphic datasets, reprocessed as part of the ALICE project, that are available through MAST. These data can help at identifying the nature of companion candidates detected by other instruments, and at refining planet or disk population statistics by combining NICMOS data with other surveys.
Citizen Science Project: Disk Detective
STScI staff are critical contributors to the Disk Detective Citizen Science Project, the first NASA led and funded Zooniverse project that has the goal of identifying protoplanetary and debris disks in the NASA's WISE mission data. | 0.842893 | 3.659478 |
A NASA space telescope tasked with probing the most powerful explosions in the universe has a new lease on life.
NASA officials said Wednesday (Aug. 21) that the Fermi Gamma-ray Space Telescope, which has just completed its initial five-year study, has officially entered an extended mission phase. The extension will allow Fermi telescope scientists to further probe the Milky Way in search of gamma-ray signals from elusive dark matter. Scientists hope the space observatory, which launched in 2008, will ultimately last a full decade in orbit, but will depend on future reviews.
"As Fermi opens its second act, both the spacecraft and its instruments remain in top-notch condition and the mission is delivering outstanding science," Paul Hertz, director of NASA's astrophysics division in Washington, D.C., said in a statement. [See photos from NASA's gamma-ray hunting Fermi Space Telescope]
Scientists working with the $690 million Fermi telescope may change up their observing strategy for the new portion of the mission.
The Large Area Telescope (LAT) instrument onboard Fermi will start to take deeper exposures of the central portion of the Milky Way. This part of the galaxy is filled with sources of high-energy like pulsars, possibly making it a great place to hunt for signals of dark matter — a mysterious substance that doesn’t emit or absorb visible light.
Some scientists suspect that dark matter could be formed from "exotic particles that produce a flash of gamma rays when they interact," NASA officials explained in a statement.
"As the LAT builds up an increasingly detailed picture of the gamma-ray sky, it simultaneously reveals how dynamic the universe is at these energies," Peter Michelson, the instrument's principal investigator and a professor of physics at Stanford University in California said.
During its five-year mission, Fermi successfully dodged space junk and helped astronomers investigate gamma-ray bursts: the most powerful explosions in the known universe.
The probe's Gamma-ray Burst Monitor (GBM) instrument sees the entire sky except for the part blocked by Earth on the lookout for these powerful bursts that could happen at any moment.
"More than 1,200 gamma-ray bursts, plus 500 flares from our sun and a few hundred flares from highly magnetized neutron stars in our galaxy have been seen by the GBM," principal investigator Bill Paciesas, a senior scientist at the Universities Space Research Association's Science and Technology Institute in Huntsville, Ala., said in a statement.
Fermi also made a surprising galactic discovery in 2010. The probe found giant bubbles stretching more than 25,000 light-years above and below the plane of the Milky Way, NASA officials said. The mysterious structures could be the result of outbursts from the supermassive black hole at the center of the galaxy.
Editor's note: This story was corrected on Aug. 23 to note that while the Fermi space telescope has entered an extended mission phase, operations all the way through 2018 are not yet final. Scientists hope the mission will last another five years, but it will depend on periodic reviews. | 0.878815 | 3.431788 |
The Sun behaves as a unipolar inductor producing a current that flows outwards along both axes B2, and inwards in the equatorial plane, C, and along Solar magnetic field lines B1. The current closes at a large distance, B3.
- “The central body acts as a unipolar inductor and the e.m.f. is produced in region A. The mechanical force on the solar atmosphere dF = I ds x B tends to decelerate the rotation of the central body. The current transfers angular momentum from the central body to the surrounding plasma. Hence, we have a decelerating force applied to the solar atmosphere in the polar region. This should produce a non-uniform rotation of the Sun of the type which is observed (angular velocity decreasing with increasing latitude.Whether this interpretation is the correct quantitative explanation of the non-uniform rotation is an open question.
- “In region B1 , the currents are field-aligned. It seems to be a general rule of cosmic physics that field-aligned currents frequently manifest themselves as luminous filaments (II.4). If the current in B1 is spread over an extended region, we should expect filaments. Equatorial streamers in the solar corona may be explained in this way. Similarly, in the polar region, the vertical currents near the solar surface may produce the polar plumes in the solar corona.
- “The model predicts that there should be currents near the axis strong enough to match the current in the equatorial plane. Such currents should be observed when a spacecraft is sent to the high latitude regions. It is an open question to what extent they flow very close to the axis. They may be distributed over a large region and may in part flow at medium latitudes.”
Galactic current circuit
Hannes Alfvén and Per Carlqvist speculate on the existence of a galactic current sheet in which the galaxy acts as a unipolar inductor, a counterpart of the heliospheric current sheet, with an estimated galactic current of 1017 – 1019 Amps, that might flow in the plane of symmetry of the galaxy.
- Hannes Alfvén, “Keynote Address (1987) Double Layers in Astrophysics, Proceedings of a Workshop held in Huntsville, Ala., 17-19 Mar. 1986. Edited by Alton C. Williams and Tauna W. Moorehead. NASA Conference Publication, #2469″ (Record | Full text)
- Alfven, H., “Double radio sources and the new approach to cosmical plasma physics” (1978) Astrophysics and Space Science, vol. 54, no. 2, Apr. 1978, p. 279-292.
- Hannes Alfvén, “The Heliospheric Current System (sec III:4)” in Cosmic Plasma, Astrophysics and Space Science Library, Vol. 82 (1981) Springer Verlag. ISBN 90-277-1151-8
- Hannes Alfvén and Per Carlqvist, “Interstellar clouds and the formation of stars” (1978) in Astrophysics and Space Science, vol. 55, no. 2, May 1978, p. 487-509.
- Israelevich, P. L, et al “MHD simulation of the three-dimensional structure of the heliospheric current sheet” (2001) Astronomy and Astrophysics, v.376, p.288-291 (Online in full) | 0.888948 | 3.880878 |
New research suggests that ice ages influence underwater volcanic eruptions which, in turn, pump large amounts of carbon dioxide into the atmosphere thus changing the earth’s temperature.
This new research could mean that the real cause of climate change, believed by many to be the result of man-made carbon dioxide emissions, may actually be the result of mother nature.
The climate-driven rise and fall of sea level during the past million years matches up with valleys and ridges on the seafloor, suggesting ice ages influence underwater volcanic eruptions, two new studies reveal. And because volcanic chains suture some 37,000 miles (59,500 kilometers) of ocean floor, the eruptions could pump out enough carbon dioxide gas to shift planetary temperatures, the study authors suggest.
“Surprisingly, the deep seafloor matters in the long-term climate cycle,” said Maya Tolstoy, lead author of one of the studies and a marine geophysicist at the Lamont-Doherty Earth Observatory in Palisades, New York.
New oceanic crust is born at underwater volcanic chains called spreading ridges, where magma (molten rock) rises to fill the gap between moving tectonic plates. Scientists think that as the plates pull away from spreading ridges, the new crust cools, cracks and sinks, creating gaps between the lines of volcanoes (which are carried away from the ridge with the plate). These parallel volcanic ridges and valleys are some of the most visible features on Earth’s ocean floor. [Infographic: Tallest Mountain to Deepest Ocean Trench]
Wrinkles in time
Tolstoy’s study at the East Pacific Rise spreading ridge, offshore western South America, found connections between ice age cycles and these seafloor corrugations that extend back 800,000 years. The bands of thicker and thinner crust correspond to 100,000-year ice age cycles — the most powerful of Earth’s freeze-and-thaw rhythms. When glaciers expanded and sea level dropped, more lava oozed from the ridge volcanoes, Tolstoy discovered. (When magma breaches the surface, itis called lava.) The thinnest crust, formed when eruptions slowed, matches up with eras of higher sea level. The findings were published today (Feb. 5) in the journal Geophysical Research Letters.
A separate study conducted at the junction between the Australia and Antarctic tectonic plates came up with similar results. For the past million years, when sea level rose, underwater eruptions slowed along the ridge. And when ice sheets expanded and sea level dropped, the lowered ocean pressure boosted volcanic activity, according to a computer model published today in the journal Science. The model suggests that water weight can change how quickly the molten rock, or magma, wells up at spreading ridges.
“When ice sheets melt and sea level goes up, it has an effect on volcanoes under the sea,” said Richard Katz, co-author of the study in Science and a geophysicist at the University of Oxford in the United Kingdom.
Earlier studies have found that volcanoes on land also surged in activity between 12,000 and 7,000 years ago, when ice sheets shrunk after the most recent cold climate swing ended.
Ice ages are driven by regular variations in Earth’s orbit. These changes in tilt, eccentricity and orbit create climate cycles that last 23,000 years; 41,000 years; and 100,000 years, respectively (at least for the previous million years). Sea level may rise and fall by some 330 feet (about 100 meters) during these climate swings.
Although eruptions along the Australia-Antarctica spreading ridge and the East Pacific Rise spreading ridge continued whether sea level was high or low, there were pulses of volcanic activity that corresponded to each of these three ice age cycles, both studies reported. The 100,000-year ice age cycle created the most prominent changes in the seafloor crust.
Until now, scientists had assumed that seafloor volcanoes ooze lava at relatively steady rates through time.
Both studies suggest that there could be a complex feedback loop among ice ages, sea level changes and these bursts of volcanic activity. For instance, if volcanoes pick up their pace during an ice age, then carbon dioxide gas could warm the Earth and shrink the ice sheets. (Underwater volcanoes pump carbon dioxide into the ocean, just as their terrestrial cousins add climate-altering gases to the atmosphere.) However, no one knows how much gas would escape into the atmosphere from the oceans.
“In a broad sense, this reinforces the idea that the climate system and the solid Earth are connected and, in fact, may be thought of as a single system,” Katz said. “Not only do ice ages affect volcanism, but volcanism has a feedback effect on climate itself. We haven’t proved that yet, but it’s a tantalizing possibility.”
Tolstoy summarized the results from the East Pacific Rise and from closely monitored submarine eruptions around the world. The findings in Science, led by University of Oxford researcher John Crowley, are based on ocean floor surveys gathered by a Korean icebreaker in 2011 and 2013. Both studies rely on high-resolution spectral imaging of the seafloor, a remote-sensing technique that maps the surface in great detail.
“Both of these data sets have found a signal which is consistent with climate forcing of variations at midocean ridges,” said Paul Asimow, a geology professor at the California Institute of Technology in Pasadena who was not involved in either study. “Now, apart from showing the effect is there, the other part that needs to be teased out is its consequences.”
The authors of each study are now searching for additional ice age signals at other spreading ridges, such as the Juan de Fuca Ridge offshore Washington and Oregon.
Latest posts by Sean Adl-Tabatabai (see all)
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- Ilhan Omar: It’s Time to Disband Minneapolis Police Dept - June 6, 2020 | 0.850529 | 3.182086 |
|Died||8 July 1695 (aged 66)|
The Hague, Dutch Republic
|Alma mater||University of Leiden|
University of Angers
Explanation of Saturn's rings
31 equal temperament musical tuning
|Fields||Natural Philosophy |
|Institutions||Royal Society of London|
French Academy of Sciences
Frans van Schooten
|Influenced||Gottfried Wilhelm Leibniz|
Christiaan Huygens // HY-gənz, also US: // HOY-gənz, Dutch: [ˈkrɪstijaːn ˈɦœyɣə(n)s] (listen); Latin: Hugenius; 14 April 1629 – 8 July 1695), also spelled Huyghens, was a Dutch physicist, mathematician, astronomer and inventor, who is widely regarded as one of the greatest scientists of all time and a major figure in the scientific revolution. In physics, Huygens made groundbreaking contributions in optics and mechanics, while as an astronomer he is chiefly known for his studies of the rings of Saturn and the discovery of its moon Titan. As an inventor, he improved the design of the telescope with the invention of the Huygenian eyepiece. His most famous invention, however, was the pendulum clock in 1656, which was a breakthrough in timekeeping and became the most accurate timekeeper for almost 300 years. Huygens was an outstanding mathematician and, because he was the first to transfer mathematical inquiry to describe unobservable physical phenomena, he has been called the first theoretical physicist and the founder of mathematical physics.(
In 1659, Huygens was the first to derive geometrically the now standard formulae for the centripetal force and centrifugal force in his work De vi centrifuga. The formulae played a central role in classical mechanics. Huygens was also the first to identify the correct laws of elastic collision in his work De motu corporum ex percussione, but his findings were not published until 1703, after his death. In the field of optics, he is best known for his wave theory of light, which he proposed in 1678 and described in 1690 in his Treatise on Light, which is regarded as the first mathematical theory of light. His theory was initially rejected in favor of Isaac Newton's corpuscular theory of light, until Augustin-Jean Fresnel adopted Huygens' principle in 1818 and showed that it could explain the rectilinear propagation and diffraction effects of light. Today this principle is known as the Huygens–Fresnel principle.
Huygens invented the pendulum clock in 1656, which he patented the following year. In addition to this invention, his research in horology resulted in an extensive analysis of the pendulum in his 1673 book Horologium Oscillatorium, which is regarded as one of the most important 17th-century works in mechanics. While the first part of the book contains descriptions of clock designs, most of the book is an analysis of pendulum motion and a theory of curves. In 1655, Huygens began grinding lenses with his brother Constantijn in order to build telescopes to conduct astronomical research. He designed a 50-power refracting telescope with which he discovered that the ring of Saturn was "a thin, flat ring, nowhere touching, and inclined to the ecliptic." It was with this telescope that he also discovered the first of Saturn's moons, Titan. He eventually developed in 1662 what is now called the Huygenian eyepiece, a telescope with two lenses, which diminished the amount of dispersion.
As a mathematician, Huygens developed the theory of evolutes and was a pioneer on probability, writing his first treatise on probability theory in 1657 entitled Van Rekeningh in Spelen van Gluck. Frans van Schooten, who was the private tutor of Huygens, translated the work as De ratiociniis in ludo aleae ("On Reasoning in Games of Chance"). The work is a systematic treatise on probability and deals with games of chance and in particular the problem of points. The modern concept of probability grew out of the use of expectation values by Huygens and Blaise Pascal (who encouraged him to write the work).
Christiaan Huygens was born on 14 April 1629 in The Hague, into a rich and influential Dutch family, the second son of Constantijn Huygens. Christiaan was named after his paternal grandfather. His mother was Suzanna van Baerle. She died in 1637, shortly after the birth of Huygens' sister. The couple had five children: Constantijn (1628), Christiaan (1629), Lodewijk (1631), Philips (1632) and Suzanna (1637).
Constantijn Huygens was a diplomat and advisor to the House of Orange, and also a poet and musician. His friends included Galileo Galilei, Marin Mersenne and René Descartes. Huygens was educated at home until turning sixteen years old. He liked to play with miniatures of mills and other machines. His father gave him a liberal education: he studied languages and music, history and geography, mathematics, logic and rhetoric, but also dancing, fencing and horse riding.
In 1644 Huygens had as his mathematical tutor Jan Jansz de Jonge Stampioen, who set the 15-year-old a demanding reading list on contemporary science. Descartes was impressed by his skills in geometry.
His father sent Huygens to study law and mathematics at the University of Leiden, where he studied from May 1645 to March 1647. Frans van Schooten was an academic at Leiden from 1646, and also a private tutor to Huygens and his elder brother, replacing Stampioen on the advice of Descartes. Van Schooten brought his mathematical education up to date, in particular introducing him to the work of Fermat on differential geometry.
After two years, from March 1647, Huygens continued his studies at the newly founded Orange College, in Breda, where his father was a curator: the change occurred because of a duel between his brother Lodewijk and another student. Constantijn Huygens was closely involved in the new College, which lasted only to 1669; the rector was André Rivet. Christiaan Huygens lived at the home of the jurist Johann Henryk Dauber, and had mathematics classes with the English lecturer John Pell. He completed his studies in August 1649. He then had a stint as a diplomat on a mission with Henry, Duke of Nassau. It took him to Bentheim, then Flensburg. He took off for Denmark, visited Copenhagen and Helsingør, and hoped to cross the Øresund to visit Descartes in Stockholm. It was not to be.
While his father Constantijn had wished his son Christiaan to be a diplomat, it also was not to be. In political terms, the First Stadtholderless Period that began in 1650 meant that the House of Orange was not in power, removing Constantijn's influence. Further, he realised that his son had no interest in such a career.
Huygens generally wrote in French or Latin. While still a college student at Leiden he began a correspondence with the intelligencer Mersenne, who died quite soon afterwards in 1648. Mersenne wrote to Constantijn on his son's talent for mathematics, and flatteringly compared him to Archimedes (3 January 1647). The letters show the early interests of Huygens in mathematics. In October 1646 there is the suspension bridge, and the demonstration that a catenary is not a parabola. In 1647/8 they cover the claim of Grégoire de Saint-Vincent to squaring the circle; rectification of the ellipse; projectiles, and the vibrating string. Some of Mersenne's concerns at the time, such as the cycloid (he sent Evangelista Torricelli's treatise on the curve), the centre of oscillation, and the gravitational constant, were matters Huygens only took seriously towards the end of the 17th century. Mersenne had also written on musical theory. Huygens preferred meantone temperament; he innovated in 31 equal temperament, which was not itself a new idea but known to Francisco de Salinas, using logarithms to investigate it further and show its close relation to the meantone system.
In 1654, Huygens returned to his father's house in The Hague, and was able to devote himself entirely to research. The family had another house, not far away at Hofwijck, and he spent time there during the summer. His scholarly life did not allow him to escape bouts of depression.
Subsequently, Huygens developed a broad range of correspondents, though picking up the threads after 1648 was hampered by the five-year Fronde in France. Visiting Paris in 1655, Huygens called on Ismael Boulliau to introduce himself. Then Boulliau took him to see Claude Mylon. The Parisian group of savants that had gathered around Mersenne held together into the 1650s, and Mylon, who had assumed the secretarial role, took some trouble from then on to keep Huygens in touch. Through Pierre de Carcavi Huygens corresponded in 1656 with Pierre de Fermat, whom he admired greatly, though this side of idolatry. The experience was bittersweet and even puzzling, since it became clear that Fermat had dropped out of the research mainstream, and his priority claims could probably not be made good in some cases. Besides, Huygens was looking by then to apply mathematics, while Fermat's concerns ran to purer topics.
Huygens was often slow to publish his results and discoveries. In the early days his mentor Frans van Schooten was cautious for the sake of his reputation.
The first work Huygens put in print was Theoremata de quadratura (1651) in the field of quadrature. It included material discussed with Mersenne some years before, such as the fallacious nature of the squaring of the circle by Grégoire de Saint-Vincent. His preferred methods were those of Archimedes and Fermat. Quadrature was a live issue in the 1650s, and through Mylon, Huygens intervened in the discussion of the mathematics of Thomas Hobbes. Persisting in trying to explain the errors Hobbes had fallen into, he made an international reputation.
Huygens studied spherical lenses from a theoretical point of view in 1652–3, obtaining results that remained unpublished until Isaac Barrow (1669). His aim was to understand telescopes. He began grinding his own lenses in 1655, collaborating with his brother Constantijn. He designed in 1662 what is now called the Huygenian eyepiece, with two lenses, as a telescope ocular. Lenses were also a common interest through which Huygens could meet socially in the 1660s with Baruch Spinoza, who ground them professionally. They had rather different outlooks on science, Spinoza being the more committed Cartesian, and some of their discussion survives in correspondence. He encountered the work of Antoni van Leeuwenhoek, another lens grinder, in the field of microscopy which interested his father.
Huygens wrote the first treatise on probability theory, De ratiociniis in ludo aleae ("On Reasoning in Games of Chance", 1657). He had been told of recent work in the field by Fermat, Blaise Pascal and Girard Desargues two years earlier, in Paris. Frans van Schooten translated the original Dutch manuscript "Van Rekeningh in Spelen van Geluck" into Latin and published it in his Exercitationum mathematicarum. It deals with games of chance, in particular the problem of points. Huygens took as intuitive his appeals to concepts of a "fair game" and equitable contract, and used them to set up a theory of expected values. In 1662 Sir Robert Moray sent Huygens John Graunt's life table, and in time Huygens and his brother Lodewijk worked on life expectancy.
On 3 May 1661, Huygens observed the planet Mercury transit over the Sun, using the telescope of instrument maker Richard Reeve in London, together with astronomer Thomas Streete and Reeve. Streete then debated the published record of the transit of Hevelius, a controversy mediated by Henry Oldenburg. Huygens passed to Hevelius a manuscript of Jeremiah Horrocks on the transit of Venus, 1639, which thereby was printed for the first time in 1662. In that year Huygens, who played the harpsichord, took an interest in music, and Simon Stevin's theories on it; he showed very little concern to publish his theories on consonance, some of which were lost for centuries. The Royal Society of London elected him a Fellow in 1663.
The Montmor Academy was the form the old Mersenne circle took after the mid-1650s. Huygens took part in its debates, and supported its "dissident" faction who favoured experimental demonstration to curtail fruitless discussion, and opposed amateurish attitudes. During 1663 he made what was his third visit to Paris; the Montmor Academy closed down, and Huygens took the chance to advocate a more Baconian programme in science. In 1666 he moved to Paris and earned a position at Louis XIV's new French Academy of Sciences.
In Paris Huygens had an important patron and correspondent in Jean-Baptiste Colbert. However, his relationship with the Academy was not always easy, and in 1670 Huygens, seriously ill, chose Francis Vernon to carry out a donation of his papers to the Royal Society in London, should he die. Then the Franco-Dutch War took place (1672–8). England's part in it (1672–4) is thought to have damaged his relationship with the Royal Society. Robert Hooke for the Royal Society lacked the urbanity to handle the situation, in 1673.
Denis Papin was assistant to Huygens from 1671. One of their projects, which did not bear fruit directly, was the gunpowder engine. Papin moved to England in 1678, and continued to work in this area. Using the Paris Observatory (completed in 1672), Huygens made further astronomical observations. In 1678 he introduced Nicolaas Hartsoeker to French scientists such as Nicolas Malebranche and Giovanni Cassini.
It was in Paris, also, that Huygens met the young diplomat Gottfried Leibniz, there in 1672 on a vain mission to meet Arnauld de Pomponne, the French Foreign Minister. At this time Leibniz was working on a calculating machine, and he moved on to London in early 1673 with diplomats from Mainz; but from March 1673 Leibniz was tutored in mathematics by Huygens. Huygens taught him analytical geometry; an extensive correspondence ensued, in which Huygens showed reluctance to accept the advantages of infinitesimal calculus.
Huygens moved back to The Hague in 1681 after suffering serious depressive illness. In 1684, he published Astroscopia Compendiaria on his new tubeless aerial telescope. He attempted to return to France in 1685 but the revocation of the Edict of Nantes precluded this move. His father died in 1687, and he inherited Hofwijck, which he made his home the following year.
Huygens observed the acoustical phenomenon now known as flanging in 1693. He died in The Hague on 8 July 1695, and was buried in an unmarked grave in the Grote Kerk there, as was his father before him.
Huygens never married.
Work in natural philosophy
Huygens has been called the leading European natural philosopher between Descartes and Newton. He adhered to the tenets of the mechanical philosophy of his time. In particular he sought explanations of the force of gravity that avoided action at a distance.
In common with Robert Boyle and Jacques Rohault, Huygens adhered to what has been called, more explicitly, "experimentally oriented corpuscular-mechanical" natural philosophy. In the analysis of the Scientific Revolution this appears as a mainstream position, at least from the founding of the Royal Society to the emergence of Newton, and was sometimes labelled "Baconian", while not being inductivist or identifying with the views of Francis Bacon in a simple-minded way. After his first visit to England in 1661, when he attended a meeting of the Gresham College group in April and learned directly about Boyle's air pump experiments, Huygens spent time in late 1661 and early 1662 replicating the work. It proved a long process, brought to the surface an experimental issue ("anomalous suspension") and the theoretical issue of horror vacui, and ended in July 1663 as Huygens became a Fellow of the Royal Society. It has been said that Huygens finally accepted Boyle's view of the void, as against the Cartesian denial of it; and also (in Leviathan and the Air Pump) that the replication of results trailed off messily.
Laws of motion, impact and gravitation
The general approach of the mechanical philosophers was to postulate theories of the kind now called "contact action". Huygens adopted this method, but not without seeing its difficulties and failures. Leibniz, his student in Paris, abandoned the theory. Seeing the universe this way made the theory of collisions central to physics. The requirements of the mechanical philosophy, in the view of Huygens, were stringent. Matter in motion made up the universe, and only explanations in those terms could be truly intelligible. While he was influenced by the Cartesian approach, he was less doctrinaire. He studied elastic collisions in the 1650s but delayed publication for over a decade.
Huygens concluded quite early that Descartes's laws for the elastic collision of two bodies must be wrong, and he formulated the correct laws. An important step was his recognition of the Galilean invariance of the problems. His views then took many years to be circulated. He passed them on in person to William Brouncker and Christopher Wren in London, in 1661. What Spinoza wrote to Henry Oldenburg about them, in 1666 which was during the Second Anglo-Dutch War, was guarded. Huygens had actually worked them out in a manuscript De motu corporum ex percussione in the period 1652–6. The war ended in 1667, and Huygens announced his results to the Royal Society in 1668. He published them in the Journal des sçavans in 1669.
Huygens stated what is now known as the second of Newton's laws of motion in a quadratic form. In 1659 he derived the now standard formula for the centripetal force, exerted on an object describing a circular motion, for instance by the string to which it is attached. In modern notation:
with m the mass of the object, v the velocity and r the radius. The publication of the general formula for this force in 1673 was a significant step in studying orbits in astronomy. It enabled the transition from Kepler's third law of planetary motion, to the inverse square law of gravitation. The interpretation of Newton's work on gravitation by Huygens differed, however, from that of Newtonians such as Roger Cotes; he did not insist on the a priori attitude of Descartes, but neither would he accept aspects of gravitational attractions that were not attributable in principle to contact of particles.
The approach used by Huygens also missed some central notions of mathematical physics, which were not lost on others. His work on pendulums came very close to the theory of simple harmonic motion; but the topic was covered fully for the first time by Newton, in Book II of his Principia Mathematica (1687). In 1678 Leibniz picked out of Huygens's work on collisions the idea of conservation law that Huygens had left implicit.
Huygens is remembered especially for his wave theory of light, which he first communicated in 1678 to the Paris Académie des sciences. It was published in 1690 in his Traité de la lumière (Treatise on light), making it the first mathematical theory of light. He refers to Ignace-Gaston Pardies, whose manuscript on optics helped him on his wave theory.
Huygens assumes that the speed of light is finite, as had been shown in an experiment by Ole Christensen Roemer in 1679, but which Huygens is presumed to have already believed. The challenge for the wave theory of light at that time was to explain geometrical optics, as most physical optics phenomena (such as diffraction) had not been observed or appreciated as issues. It posits light radiating wavefronts with the common notion of light rays depicting propagation normal to those wavefronts. Propagation of the wavefronts is then explained as the result of spherical waves being emitted at every point along the wave front (the Huygens–Fresnel principle). It assumed an omnipresent ether, with transmission through perfectly elastic particles, a revision of the view of Descartes. The nature of light was therefore a longitudinal wave.
Huygens had experimented in 1672 with double refraction (birefringence) in Icelandic spar (calcite), a phenomenon discovered in 1669 by Rasmus Bartholin. At first he could not elucidate what he found. He later explained it with his wave front theory and concept of evolutes. He also developed ideas on caustics. Newton in his Opticks of 1704 proposed instead a corpuscular theory of light. The theory of Huygens was not widely accepted, one strong objection being that longitudinal waves have only a single polarization which cannot explain the observed birefringence. However the 1801 interference experiments of Thomas Young and François Arago's 1819 detection of the Poisson spot could not be explained through any particle theory, reviving the ideas of Huygens and wave models. In 1821 Fresnel was able to explain birefringence as a result of light being not a longitudinal (as had been assumed) but actually a transverse wave. The thus-named Huygens–Fresnel principle was the basis for the advancement of physical optics, explaining all aspects of light propagation. It was only understanding the detailed interaction of light with atoms that awaited quantum mechanics and the discovery of the photon.
Huygens investigated the use of lenses in projectors. He is credited as the inventor of the magic lantern, described in correspondence of 1659. There are others to whom such a lantern device has been attributed, such as Giambattista della Porta, and Cornelis Drebbel: the point at issue is the use of a lens for better projection. Athanasius Kircher has also been credited for that.
Huygens designed more accurate clocks than were available at the time. In 1656, inspired by earlier research into pendulums by Galileo Galilei, he invented the pendulum clock, which was a breakthrough in timekeeping and became the most accurate timekeeper for the next 275 years until the 1930s. Huygens contracted the construction of his clock designs to Salomon Coster in The Hague, who built the clock. The pendulum clock was much more accurate than the existing verge and foliot clocks and was immediately popular, quickly spreading over Europe. However Huygens did not make much money from his invention. Pierre Séguier refused him any French rights, Simon Douw of Rotterdam copied the design in 1658, and Ahasuerus Fromanteel also, in London. The oldest known Huygens-style pendulum clock is dated 1657 and can be seen at the Museum Boerhaave in Leiden.
Huygens motivation for inventing the pendulum clock was to create an accurate marine chronometer that could be used to find longitude by celestial navigation during sea voyages. However the clock proved unsuccessful as a marine timekeeper because the rocking motion of the ship disturbed the motion of the pendulum. In 1660 Lodewijk Huygens made a trial on a voyage to Spain, and reported that heavy weather made the clock useless. Alexander Bruce elbowed into the field in 1662, and Huygens called in Sir Robert Moray and the Royal Society to mediate and preserve some of his rights. Trials continued into the 1660s, the best news coming from a Royal Navy captain Robert Holmes operating against the Dutch possessions in 1664. Lisa Jardine doubts that Holmes reported the results of the trial accurately, and Samuel Pepys expressed his doubts at the time: The said master [i.e. the captain of Holmes' ship] affirmed, that the vulgar reckoning proved as near as that of the watches, which [the clocks], added he, had varied from one another unequally, sometimes backward, sometimes forward, to 4, 6, 7, 3, 5 minutes; as also that they had been corrected by the usual account. One for the French Academy on an expedition to Cayenne ended badly. Jean Richer suggested correction for the figure of the Earth. By the time of the Dutch East India Company expedition of 1686 to the Cape of Good Hope, Huygens was able to supply the correction retrospectively.
In 1673 Huygens published Horologium Oscillatorium sive de motu pendulorum, his major work on pendulums and horology. It had been observed by Mersenne and others that pendulums are not quite isochronous: their period depends on their width of swing, with wide swings taking slightly longer than narrow swings.
Huygens analyzed this problem by finding the curve down which a mass will slide under the influence of gravity in the same amount of time, regardless of its starting point; the so-called tautochrone problem. By geometrical methods which were an early use of calculus, he showed it to be a cycloid, rather than the circular arc of a pendulum's bob, and therefore that pendulums are not isochronous. He also solved a problem posed by Mersenne: how to calculate the period of a pendulum made of an arbitrarily-shaped swinging rigid body. This involved discovering the centre of oscillation and its reciprocal relationship with the pivot point. In the same work, he analysed the conical pendulum, consisting of a weight on a cord moving in a circle, using the concept of centrifugal force.
Huygens was the first to derive the formula for the period of an ideal mathematical pendulum (with massless rod or cord and length much longer than its swing), in modern notation:
with T the period, l the length of the pendulum and g the gravitational acceleration. By his study of the oscillation period of compound pendulums Huygens made pivotal contributions to the development of the concept of moment of inertia.
Huygens also observed coupled oscillations: two of his pendulum clocks mounted next to each other on the same support often became synchronized, swinging in opposite directions. He reported the results by letter to the Royal Society, and it is referred to as "an odd kind of sympathy" in the Society's minutes. This concept is now known as entrainment.
Balance spring watch
Huygens developed a balance spring watch in the same period as, though independently of, Robert Hooke. Controversy over the priority persisted for centuries. A Huygens watch employed a spiral balance spring; but he used this form of spring initially only because the balance in his first watch rotated more than one and a half turns. He later used spiral springs in more conventional watches, made for him by Thuret in Paris from around 1675.
Such springs were essential in modern watches with a detached lever escapement because they can be adjusted for isochronism. Watches in the time of Huygens and Hooke, however, employed the very undetached verge escapement. It interfered with the isochronal properties of any form of balance spring, spiral or otherwise.
In February 2006, a long-lost copy of Hooke's handwritten notes from several decades of Royal Society meetings was discovered in a cupboard in Hampshire, England. The balance-spring priority controversy appears, by the evidence contained in those notes, to be settled in favour of Hooke's claim.
In 1675, Huygens patented a pocket watch. The watches which were made in Paris from c. 1675 and following the Huygens plan are notable for lacking a fusee for equalizing the mainspring torque. The implication is that Huygens thought that his spiral spring would isochronise the balance, in the same way that he thought that the cycloidally shaped suspension curbs on his clocks would isochronise the pendulum.
Saturn's rings and Titan
In 1655, Huygens proposed that Saturn was surrounded by a solid ring, "a thin, flat ring, nowhere touching, and inclined to the ecliptic." Using a 50 power refracting telescope that he designed himself, Huygens also discovered the first of Saturn's moons, Titan. In the same year he observed and sketched the Orion Nebula. His drawing, the first such known of the Orion nebula, was published in Systema Saturnium in 1659. Using his modern telescope he succeeded in subdividing the nebula into different stars. The brighter interior now bears the name of the Huygenian region in his honour. He also discovered several interstellar nebulae and some double stars.
Mars and Syrtis Major
In 1659, Huygens was the first to observe a surface feature on another planet, Syrtis Major, a volcanic plain on Mars. He used repeated observations of the movement of this feature over the course of a number of days to estimate the length of day on Mars, which he did quite accurately to 24 1/2 hours. This figure is only a few minutes off of the actual length of the Martian day of 24 hours, 37 minutes.
Shortly before his death in 1695, Huygens completed Cosmotheoros, published posthumously in 1698. In it he speculated on the existence of extraterrestrial life, on other planets, which he imagined was similar to that on Earth. Such speculations were not uncommon at the time, justified by Copernicanism or the plenitude principle. But Huygens went into greater detail, though without the benefit of understanding Newton's laws of gravitation, or the fact that the atmospheres on other planets are composed of different gases. The work, translated into English in its year of publication, has been seen as in the fanciful tradition of Francis Godwin, John Wilkins and Cyrano de Bergerac, and fundamentally Utopian; and also to owe in its concept of planet to cosmography in the sense of Peter Heylin.
Huygens wrote that availability of water in liquid form was essential for life and that the properties of water must vary from planet to planet to suit the temperature range. He took his observations of dark and bright spots on the surfaces of Mars and Jupiter to be evidence of water and ice on those planets. He argued that extraterrestrial life is neither confirmed nor denied by the Bible, and questioned why God would create the other planets if they were not to serve a greater purpose than that of being admired from Earth. Huygens postulated that the great distance between the planets signified that God had not intended for beings on one to know about the beings on the others, and had not foreseen how much humans would advance in scientific knowledge.
It was also in this book that Huygens published his method for estimating stellar distances. He made a series of smaller holes in a screen facing the Sun, until he estimated the light was of the same intensity as that of the star Sirius. He then calculated that the angle of this hole was th the diameter of the Sun, and thus it was about 30,000 times as far away, on the (incorrect) assumption that Sirius is as luminous as the Sun. The subject of photometry remained in its infancy until the time of Pierre Bouguer and Johann Heinrich Lambert.
During his lifetime
- 1639 – His father Constantijn Huygens in the midst of his five children by Adriaen Hanneman, painting with medallions, Mauritshuis, The Hague
- 1671 – Portrait by Caspar Netscher, Museum Boerhaave, Leiden, loan from Haags Historisch Museum
- ~1675 – Possible depiction of Huygens on l'French: Établissement de l'Académie des Sciences et fondation de l'observatoire, 1666 by Henri Testelin. Colbert presents the members of the newly founded Académie des Sciences to king Louis XIV of France. Musée National du Château et des Trianons de Versailles, Versailles
- 1679 – Medaillon portrait in relief by the French sculptor Jean-Jacques Clérion
- 1686 – Portrait in pastel by Bernard Vaillant, Museum Hofwijck, Voorburg
- between 1684 and 1687 – Engraving by G. Edelinck after the painting by Caspar Netscher
- 1688 – Portrait by Pierre Bourguignon (painter), Royal Netherlands Academy of Arts and Sciences, Amsterdam
Named after Huygens
- The Huygens probe: The lander for the Saturnian moon Titan, part of the Cassini–Huygens mission to Saturn
- Asteroid 2801 Huygens
- A crater on Mars
- Mons Huygens, a mountain on the Moon
- Huygens Software, a microscope image processing package.
- A two element eyepiece designed by him. An early step in the development of the achromatic lens, since it corrects some chromatic aberration.
- The Huygens–Fresnel principle, a simple model to understand disturbances in wave propagation.
- Huygens wavelets, the fundamental mathematical basis for scalar diffraction theory
- Medisch- Natuurphilosophisch en Veterinair- Tandheelkundig Gezelschap "Christiaan Huygens", scientific discussion group
- Huygens Lyceum, High School located in Eindhoven, Netherlands.
- The Christiaan Huygens, a ship of the Nederland Line.
- Huygens Scholarship Programme for international students and Dutch students
- W.I.S.V. Christiaan Huygens: Dutch study guild for the studies Mathematics and Computer Science at the Delft University of Technology
- Huygens Laboratory: Home of the Physics department at Leiden University, Netherlands
- Huygens Supercomputer: National Supercomputer facility of the Netherlands, located at SARA in Amsterdam
- The Huygens-building in Noordwijk, Netherlands, first building on the Space Business park opposite Estec (ESA)
- The Huygens-building at the Radboud University Nijmegen, the Netherlands. One of the major buildings of the science department at the university of Nijmegen.
- Christiaan Huygensplein, a square in Amsterdam
- 1649 – De iis quae liquido supernatant (About the parts above the water, unpublished)
- 1651 – Cyclometriae:102
- 1651 – Theoremata de quadratura hyperboles, ellipsis et circuli, in Oeuvres Complètes, Tome XI, link from Internet Archive.
- 1654 – De circuli magnitudine inventa
- 1656 – De Saturni Luna observatio nova (About the new observation of the moon of Saturn – discovery of Titan)
- 1656 – De motu corporum ex percussione, published only in 1703
- 1657 – De ratiociniis in ludo aleae = Van reeckening in spelen van geluck (translated by Frans van Schooten)
- 1659 – Systema saturnium (on the planet Saturn)
- 1659 – De vi centrifuga (Concerning the centrifugal force), published in 1703
- 1673 – Horologium oscillatorium sive de motu pendularium (theory and design of the pendulum clock, dedicated to Louis XIV of France) – View at the HathiTrust Digital Library
- 1684 – Astroscopia Compendiaria tubi optici molimine liberata (compound telescopes without a tube)
- 1685 – Memoriën aengaende het slijpen van glasen tot verrekijckers (How to grind telescope lenses)
- 1686 – Old Dutch: Kort onderwijs aengaende het gebruijck der horologiën tot het vinden der lenghten van Oost en West (How to use clocks to establish the longitude)
- 1690 – Traité de la lumière (translated by Silvanus P. Thompson)
- 1690 – Discours de la cause de la pesanteur (Discourse about gravity, from 1669?)
- 1691 – Lettre touchant le cycle harmonique (Rotterdam, concerning the 31-tone system)
- 1698 – Cosmotheoros (solar system, cosmology, life in the universe)
- 1703 – Opuscula posthuma including
- 1724 – Novus cyclus harmonicus (Leiden, after Huygens' death)
- 1728 – Christiani Hugenii Zuilichemii, dum viveret Zelhemii toparchae, opuscula posthuma ... (pub. 1728) Alternate title: Opera reliqua, concerning optics and physics
- 1888–1950 – Huygens, Christiaan. Oeuvres complètes. The Hague Complete work, editors D. Bierens de Haan (tome=deel 1–5), J. Bosscha (6–10), D.J. Korteweg (11–15), A.A. Nijland (15), J.A. Vollgraf (16–22).
- Tome I: Correspondance 1638–1656 (1888).
- Tome II: Correspondance 1657–1659 (1889).
- Tome III: Correspondance 1660–1661 (1890).
- Tome IV: Correspondance 1662–1663 (1891).
- Tome V: Correspondance 1664–1665 (1893).
- Tome VI: Correspondance 1666–1669 (1895).
- Tome VII: Correspondance 1670–1675 (1897).
- Tome VIII: Correspondance 1676–1684 (1899).
- Tome IX: Correspondance 1685–1690 (1901).
- Tome X: Correspondance 1691–1695 (1905).
- Tome XI: Travaux mathématiques 1645–1651 (1908).
- Tome XII: Travaux mathématiques pures 1652–1656 (1910).
- Tome XIII, Fasc. I: Dioptrique 1653, 1666 (1916).
- Tome XIII, Fasc. II: Dioptrique 1685–1692 (1916).
- Tome XIV: Calcul des probabilités. Travaux de mathématiques pures 1655–1666 (1920).
- Tome XV: Observations astronomiques. Système de Saturne. Travaux astronomiques 1658–1666 (1925).
- Tome XVI: Mécanique jusqu’à 1666. Percussion. Question de l'existence et de la perceptibilité du mouvement absolu. Force centrifuge (1929).
- Tome XVII: L’horloge à pendule de 1651 à 1666. Travaux divers de physique, de mécanique et de technique de 1650 à 1666. Traité des couronnes et des parhélies (1662 ou 1663) (1932).
- Tome XVIII: L'horloge à pendule ou à balancier de 1666 à 1695. Anecdota (1934).
- Tome XIX: Mécanique théorique et physique de 1666 à 1695. Huygens à l'Académie royale des sciences (1937).
- Tome XX: Musique et mathématique. Musique. Mathématiques de 1666 à 1695 (1940).
- Tome XXI: Cosmologie (1944).
- Tome XXII: Supplément à la correspondance. Varia. Biographie de Chr. Huygens. Catalogue de la vente des livres de Chr. Huygens (1950).
- History of the internal combustion engine
- List of largest optical telescopes historically
- Fokker Organ
- Seconds pendulum
- The meaning of this painting is explained in Wybe Kuitert "Japanese Robes, Sharawadgi, and the landscape discourse of Sir William Temple and Constantijn Huygens" Garden History, 41, 2: (2013) pp.157-176, Plates II-VI and Garden History, 42, 1: (2014) p.130 ISSN 0307-1243 Online as PDF
- I. Bernard Cohen; George E. Smith (25 April 2002). The Cambridge Companion to Newton. Cambridge University Press. p. 69. ISBN 978-0-521-65696-2. Retrieved 15 May 2013.
- Niccolò Guicciardini (2009). Isaac Newton on mathematical certainty and method. MIT Press. p. 344. ISBN 978-0-262-01317-8. Retrieved 15 May 2013.
- "Huygens, Christiaan". Lexico UK Dictionary. Oxford University Press. Retrieved 13 August 2019.
- "Huygens". Merriam-Webster Dictionary. Retrieved 13 August 2019.
- "Huygens". Random House Webster's Unabridged Dictionary.
- Dijksterhuis, F.J. (2008) Stevin, Huygens and the Dutch republic. Nieuw archief voor wiskunde, 5, pp. 100-107.https://research.utwente.nl/files/6673130/Dijksterhuis_naw5-2008-09-2-100.pdf
- Andriesse, C.D. (2005) Huygens: The Man Behind the Principle. Cambridge University Press. Cambridge: 6
- Andriesse, C.D. (2005) Huygens: The Man Behind the Principle. Cambridge University Press. Cambridge: 354
- Stephen J. Edberg (14 December 2012) Christiaan Huygens, Encyclopedia of World Biography. 2004. Encyclopedia.com.
- Henk J. M. Bos (14 December 2012) Huygens, Christiaan (Also Huyghens, Christian), Complete Dictionary of Scientific Biography. 2008. Encyclopedia.com.
- R. Dugas and P. Costabel, "Chapter Two, The Birth of a new Science" in The Beginnings of Modern Science, edited by Rene Taton, 1958,1964, Basic Books, Inc.
- Strategic Affection? Gift Exchange in Seventeenth-Century Holland, by Irma Thoen, pg 127
- Constantijn Huygens, Lord of Zuilichem (1596–1687), by Adelheid Rech
- The Heirs of Archimedes: Science and the Art of War Through the Age of Enlightenment, by Brett D. Steele, pg. 20
- entoen.nu: Christiaan Huygens 1629–1695 Science in the Golden Age
- Jozef T. Devreese (31 October 2008). 'Magic Is No Magic': The Wonderful World of Simon Stevin. WIT Press. pp. 275–6. ISBN 978-1-84564-391-1. Retrieved 24 April 2013.
- H. N. Jahnke (2003). A history of analysis. American Mathematical Soc. p. 47. ISBN 978-0-8218-9050-9. Retrieved 12 May 2013.
- Margret Schuchard (2007). Bernhard Varenius: (1622–1650). BRILL. p. 112. ISBN 978-90-04-16363-8. Retrieved 12 May 2013.
- Dictionary, p. 470.
- Christiaan Huygens – A family affair, by Bram Stoffele, pg 80.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. pp. 80–. ISBN 978-0-521-85090-2. Retrieved 23 April 2013.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. pp. 85–6. ISBN 978-0-521-85090-2. Retrieved 10 May 2013.
- Dictionary, p. 469.
- Lynn Thorndike (1 March 2003). History of Magic & Experimental Science 1923. Kessinger Publishing. p. 622. ISBN 978-0-7661-4316-6. Retrieved 11 May 2013.
- Leonhard Euler (1 January 1980). Clifford Truesdell (ed.). The Rational Mechanics of Flexible or Elastic Bodies 1638–1788: Introduction to Vol. X and XI. Springer. pp. 44–6. ISBN 978-3-7643-1441-5. Retrieved 10 May 2013.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. pp. 78–9. ISBN 978-0-521-85090-2. Retrieved 10 May 2013.
- Joella G. Yoder (8 July 2004). Unrolling Time: Christiaan Huygens and the Mathematization of Nature. Cambridge University Press. p. 12. ISBN 978-0-521-52481-0. Retrieved 10 May 2013.
- H.F. Cohen (31 May 1984). Quantifying Music: The Science of Music at the First Stage of Scientific Revolution 1580–1650. Springer. pp. 217–9. ISBN 978-90-277-1637-8. Retrieved 11 May 2013.
- H. J. M. Bos (1993). Lectures in the History of Mathematics. American Mathematical Soc. pp. 64–. ISBN 978-0-8218-9675-4. Retrieved 10 May 2013.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. p. 134. ISBN 978-0-521-85090-2. Retrieved 10 May 2013.
- Thomas Hobbes (1997). The Correspondence: 1660–1679. Oxford University Press. p. 868. ISBN 978-0-19-823748-8. Retrieved 10 May 2013.
- Michael S. Mahoney (1994). The Mathematical Career of Pierre de Fermat: 1601–1665. Princeton University Press. pp. 67–8. ISBN 978-0-691-03666-3. Retrieved 10 May 2013.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. p. 126. ISBN 978-0-521-85090-2. Retrieved 10 May 2013.
- Schoneveld, Cornelis W (1983). Intertraffic of the Mind: Studies in Seventeenth-century Anglo-Dutch Translation with a Checklist of Books Translated from English Into Dutch, 1600–1700. Brill Archive. p. 41. ISBN 978-90-04-06942-8. Retrieved 22 April 2013.
- Dictionary, p. 472.
- Robert D. Huerta (2005). Vermeer And Plato: Painting The Ideal. Bucknell University Press. p. 101. ISBN 978-0-8387-5606-5. Retrieved 24 April 2013.
- Randy O. Wayne (28 July 2010). Light and Video Microscopy. Academic Press. p. 72. ISBN 978-0-08-092128-0. Retrieved 24 April 2013.
- Dictionary, p. 473.
- Margaret Gullan-Whur (1998). Within Reason: A Life of Spinoza. Jonathan Cape. pp. 170–1. ISBN 0-224-05046-X.
- Ivor Grattan-Guinness (11 February 2005). Landmark Writings in Western Mathematics 1640–1940. Elsevier. p. 35. ISBN 978-0-08-045744-4. Retrieved 27 April 2013.
- p963-965, Jan Gullberg, Mathematics from the birth of numbers, W. W. Norton & Company; ISBN 978-0-393-04002-9
- Thomas Hobbes (1997). The Correspondence: 1660–1679. Oxford University Press. p. 841. ISBN 978-0-19-823748-8. Retrieved 11 May 2013.
- Garber and Ayers, p. 1124–5.
- Anders Hald (25 February 2005). A History of Probability and Statistics and Their Applications before 1750. John Wiley & Sons. p. 106. ISBN 978-0-471-72517-6. Retrieved 11 May 2013.
- Peter Louwman, Christiaan Huygens and his telescopes, Proceedings of the International Conference, 13 – 17 April 2004, ESTEC, Noordwijk, Netherlands, ESA, sp 1278, Paris 2004
- Adrian Johns (15 May 2009). The Nature of the Book: Print and Knowledge in the Making. University of Chicago Press. pp. 437–8. ISBN 978-0-226-40123-2. Retrieved 23 April 2013.
- Venus Seen on the Sun: The First Observation of a Transit of Venus by Jeremiah Horrocks. BRILL. 2 March 2012. p. xix. ISBN 978-90-04-22193-2. Retrieved 23 April 2013.
- Jozef T. Devreese (2008). 'Magic Is No Magic': The Wonderful World of Simon Stevin. WIT Press. p. 277. ISBN 978-1-84564-391-1. Retrieved 11 May 2013.
- Fokko Jan Dijksterhuis (1 October 2005). Lenses And Waves: Christiaan Huygens and the Mathematical Science of Optics in the Seventeenth Century. Springer. p. 98. ISBN 978-1-4020-2698-0. Retrieved 11 May 2013.
- Gerrit A. Lindeboom (1974). Boerhaave and Great Britain: Three Lectures on Boerhaave with Particular Reference to His Relations with Great Britain. Brill Archive. p. 15. ISBN 978-90-04-03843-1. Retrieved 11 May 2013.
- David J. Sturdy (1995). Science and Social Status: The Members of the "Académie Des Sciences", 1666–1750. Boydell & Brewer. p. 17. ISBN 978-0-85115-395-7. Retrieved 11 May 2013.
- The anatomy of a scientific institution: the Paris Academy of Sciences, 1666–1803. University of California Press. 1971. p. 7 note 12. ISBN 978-0-520-01818-1. Retrieved 27 April 2013.
- David J. Sturdy (1995). Science and Social Status: The Members of the "Académie Des Sciences", 1666–1750. Boydell & Brewer. pp. 71–2. ISBN 978-0-85115-395-7. Retrieved 27 April 2013.
- Jacob Soll (2009). The information master: Jean-Baptiste Colbert's secret state intelligence system. University of Michigan Press. p. 99. ISBN 978-0-472-11690-4. Retrieved 27 April 2013.
- A. E. Bell, Christian Huygens (1950), pp. 65–6; archive.org.
- Jonathan I. Israel (12 October 2006). Enlightenment Contested : Philosophy, Modernity, and the Emancipation of Man 1670–1752: Philosophy, Modernity, and the Emancipation of Man 1670–1752. OUP Oxford. p. 210. ISBN 978-0-19-927922-7. Retrieved 11 May 2013.
- Lisa Jardine (2003). The Curious Life of Robert Hooke. HarperCollins. pp. 180–3. ISBN 0-00-714944-1.
- Joseph Needham (1974). Science and Civilisation in China: Military technology : the gunpowder epic. Cambridge University Press. p. 556. ISBN 978-0-521-30358-3. Retrieved 22 April 2013.
- Joseph Needham (1986). Military Technology: The Gunpowder Epic. Cambridge University Press. p. xxxi. ISBN 978-0-521-30358-3. Retrieved 22 April 2013.
- Alfred Rupert Hall (1952). Ballistics in the Seventeenth Century: A Study in the Relations of Science and War with Reference Principally to England. CUP Archive. p. 63. GGKEY:UT7XX45BRJX. Retrieved 22 April 2013.
- Gottfried Wilhelm Freiherr von Leibniz (7 November 1996). Leibniz: New Essays on Human Understanding. Cambridge University Press. p. lxxxiii. ISBN 978-0-521-57660-4. Retrieved 23 April 2013.
- Marcelo Dascal (2010). The practice of reason. John Benjamins Publishing. p. 45. ISBN 978-90-272-1887-2. Retrieved 23 April 2013.
- Alfred Rupert Hall (1886). Isaac Newton: Adventurer in thought. Cambridge University Press. p. 232. ISBN 0-521-56669-X.
- Curtis ROADS (1996). The computer music tutorial. MIT Press. p. 437. ISBN 978-0-262-68082-0. Retrieved 11 May 2013.
- "GroteKerkDenHaag.nl" (in Dutch). GroteKerkDenHaag.nl. Retrieved 13 June 2010.
- "never married; from google (christiaan huygens never married) result 1".
- Anders Hald (25 February 2005). A History of Probability and Statistics and Their Applications before 1750. John Wiley & Sons. p. 123. ISBN 978-0-471-72517-6. Retrieved 11 May 2013.
- William L. Harper (8 December 2011). Isaac Newton's Scientific Method: Turning Data into Evidence about Gravity and Cosmology. Oxford University Press. pp. 206–7. ISBN 978-0-19-957040-9. Retrieved 23 April 2013.
- R. C. Olby; G. N. Cantor; J. R. R. Christie; M. J. S. Hodge (1 June 2002). Companion to the History of Modern Science. Taylor & Francis. pp. 238–40. ISBN 978-0-415-14578-7. Retrieved 12 May 2013.
- David B. Wilson (1 January 2009). Seeking nature's logic. Penn State Press. p. 19. ISBN 978-0-271-04616-7. Retrieved 12 May 2013.
- Stephen Shapin; Simon Schaffer (1989). Leviathan and the Air Pump. Princeton University Press. pp. 235–56. ISBN 0-691-02432-4.
- Deborah Redman (1997). The Rise of Political Economy As a Science: Methodology and the Classical Economists. MIT Press. p. 62. ISBN 978-0-262-26425-9. Retrieved 12 May 2013.
- Tian Yu Cao (14 May 1998). Conceptual Developments of 20th Century Field Theories. Cambridge University Press. pp. 25–. ISBN 978-0-521-63420-5. Retrieved 11 May 2013.
- Garber and Ayers, p. 595.
- Peter Dear (15 September 2008). The Intelligibility of Nature: How Science Makes Sense of the World. University of Chicago Press. p. 25. ISBN 978-0-226-13950-0. Retrieved 23 April 2013.
- The Beginnings of Modern Science, edited by Rene Taton, Basic Books, 1958, 1964.
- Garber and Ayers, pp. 666–7.
- Garber and Ayers, p. 689.
- Jonathan I. Israel (8 February 2001). Radical Enlightenment:Philosophy and the Making of Modernity 1650–1750. Oxford University Press. pp. lxii–lxiii. ISBN 978-0-19-162287-8. Retrieved 11 May 2013.
- Ernst Mach, The Science of Mechanics (1919), e.g. pp. 143, 172, 187 <https://archive.org/details/scienceofmechani005860mbp>.
- J. B. Barbour (1989). Absolute Or Relative Motion?: The discovery of dynamics. CUP Archive. p. 542. ISBN 978-0-521-32467-0. Retrieved 23 April 2013.
- A.I. Sabra (1981). Theories of light: from Descartes to Newton. CUP Archive. pp. 166–9. ISBN 978-0-521-28436-3. Retrieved 23 April 2013.
- Richard Allen (1999). David Hartley on human nature. SUNY Press. p. 98. ISBN 978-0-7914-9451-6. Retrieved 12 May 2013.
- Nicholas Jolley (1995). The Cambridge Companion to Leibniz. Cambridge University Press. p. 279. ISBN 978-0-521-36769-1. Retrieved 12 May 2013.
- Christiaan Huygens, Traité de la lumiere... (Leiden, Netherlands: Pieter van der Aa, 1690), Chapter 1.
- C. Huygens (1690), translated by Silvanus P. Thompson (1912), Treatise on Light, London: Macmillan, 1912; Project Gutenberg edition, 2005; Errata, 2016.
- Traité de la lumiere... (Leiden, Netherlands: Pieter van der Aa, 1690), Chapter 1. From page 18
- A. Mark Smith (1987). Descartes's Theory of Light and Refraction: A Discourse on Method. American Philosophical Society. p. 70 with note 10. ISBN 978-0-87169-773-8. Retrieved 11 May 2013.
- Shapiro, p. 208.
- Ivor Grattan-Guinness (11 February 2005). Landmark Writings in Western Mathematics 1640–1940. Elsevier. p. 43. ISBN 978-0-08-045744-4. Retrieved 23 April 2013.
- Darryl J. Leiter; Sharon Leiter (1 January 2009). A to Z of Physicists. Infobase Publishing. p. 108. ISBN 978-1-4381-0922-0. Retrieved 11 May 2013.
- Jordan D. Marché (2005). Theaters Of Time And Space: American Planetariums, 1930–1970. Rutgers University Press. p. 11. ISBN 978-0-8135-3576-0. Retrieved 23 April 2013.
- C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. p. 128. ISBN 978-0-521-85090-2. Retrieved 23 April 2013.
- Marrison, Warren (1948). "The Evolution of the Quartz Crystal Clock". Bell System Technical Journal. 27 (3): 510–588. doi:10.1002/j.1538-7305.1948.tb01343.x. Archived from the original on 13 May 2007.
- Epstein/Prak (2010). Guilds, Innovation and the European Economy, 1400–1800. Cambridge University Press. pp. 269–70. ISBN 978-1-139-47107-7. Retrieved 10 May 2013.
- Hans van den Ende: "Huygens's Legacy, The Golden Age of the Pendulum Clock", Fromanteel Ldt., 2004,
- van Kersen, Frits & van den Ende, Hans: Oppwindende Klokken – De Gouden Eeuw van het Slingeruurwerk 12 September – 29 November 2004 [Exhibition Catalog Paleis Het Loo]; Apeldoorn: Paleis Het Loo,2004,
- Hooijmaijers, Hans; Telling time – Devices for time measurement in museum Boerhaave – A Descriptive Catalogue; Leiden: Museum Boerhaave, 2005
- No Author given; Chistiaan Huygens 1629–1695, Chapter 1: Slingeruurwerken; Leiden: Museum Boerhaave, 1988
- Joella G. Yoder (8 July 2004). Unrolling Time: Christiaan Huygens and the Mathematization of Nature. Cambridge University Press. p. 152. ISBN 978-0-521-52481-0. Retrieved 12 May 2013.
- Michael R. Matthews (2000). Time for Science Education: How Teaching the History and Philosophy of Pendulum Motion Can Contribute to Science Literacy. Springer. pp. 137–8. ISBN 978-0-306-45880-4. Retrieved 12 May 2013.
- Lisa Jardine (1 April 2008). "Chapter 10". Going Dutch: How the English Plundered Holland's Glory. HarperPress. ISBN 978-0007197323.
- Dictionary, p. 471.
- "Boerhaave Museum Top Collection: Hague clock (Pendulum clock) (Room 3/Showcase V20)". Museumboerhaave.nl. Archived from the original on 19 February 2011. Retrieved 13 June 2010.
- "Boerhaave Museum Top Collection: Horologium oscillatorium, siue, de motu pendulorum ad horologia aptato demonstrationes geometricae (Room 3/Showcase V20)". Museumboerhaave.nl. Archived from the original on 20 February 2011. Retrieved 13 June 2010.
- Marin Mersenne 1647 Reflectiones Physico-Mathematicae, Paris, Chapter 19, cited in Mahoney, Michael S. (1980). "Christian Huygens: The Measurement of Time and of Longitude at Sea". Studies on Christiaan Huygens. Swets. pp. 234–270. Archived from the original on 4 December 2007. Retrieved 7 October 2010.
- Matthews, Michael R. (2000). Time for science education: how teaching the history and philosophy of pendulum motion can contribute to science literacy. New York: Springer. pp. 124–126. ISBN 0-306-45880-2.
- Thomas Birch, "The History of the Royal Society of London, for Improving of Natural Knowledge, in which the most considerable of those papers...as a supplement to the Philosophical Transactions", vol 2, (1756) p 19.
- A copy of the letter appears in C. Huygens, in Oeuvres Completes de Christian Huygens, edited by M. Nijhoff (Societe Hollandaise des Sciences, The Hague, The Netherlands, 1893), Vol. 5, p. 246 (in French).
- Nature – International Weekly Journal of Science, number 439, pages 638–639, 9 February 2006
- Notes and Records of the Royal Society (2006) 60, pages 235–239, 'Report – The Return of the Hooke Folio' by Robyn Adams and Lisa Jardine
- Ron Baalke, Historical Background of Saturn's Rings Archived 21 March 2009 at the Wayback Machine
- Antony Cooke (1 January 2005). Visual Astronomy Under Dark Skies: A New Approach to Observing Deep Space. Springer. p. 67. ISBN 978-1-84628-149-5. Retrieved 24 April 2013.
- Philip C. Almond (27 November 2008). Adam and Eve in Seventeenth-Century Thought. Cambridge University Press. pp. 61–2. ISBN 978-0-521-09084-1. Retrieved 24 April 2013.
- Postmus, Bouwe (1987). "Plokhoy's A way pronouned: Mennonite Utopia or Millennium?". In Dominic Baker-Smith; Cedric Charles Barfoot (eds.). Between dream and nature: essays on utopia and dystopia. Amsterdam: Rodopi. pp. 86–8. ISBN 978-90-6203-959-3. Retrieved 24 April 2013.
- Juliet Cummins; David Burchell (2007). Science, Literature, and Rhetoric in Early Modern England. Ashgate Publishing, Ltd. pp. 194–5. ISBN 978-0-7546-5781-1. Retrieved 24 April 2013.
- "Johar Huzefa (2009) Nothing But The Facts – Christiaan Huygens". Brighthub.com. 28 September 2009. Retrieved 13 June 2010.
- Jacob, Margaret (2010). The Scientific Revolution. Boston: Bedford/St. Martin's. pp. 29, 107–114.
- Russell Mccormmach (2012). Weighing the World: The Reverend John Michell of Thornhill. Springer. pp. 129–31. ISBN 978-94-007-2022-0. Retrieved 12 May 2013.
- Verduin, C.J. Kees (31 March 2009). "Portraits of Christiaan Huygens (1629–1695)". University of Leiden. Retrieved 12 April 2018.
- Verduin, C.J. (2004). "A portrait of Christiaan Huygens together with Giovanni Domenico Cassini". In Karen, Fletcher (ed.). Titan – from discovery to encounter. Noordwijk, Netherlands: ESA Publications Division. pp. 157–170. Bibcode:2004ESASP1278..157V. ISBN 92-9092-997-9.
- L, H (1907). "Christiaan Huygens, Traité: De iis quae liquido supernatant". Nature. 76 (1972): 381. Bibcode:1907Natur..76..381L. doi:10.1038/076381a0.
- Yoder, Joella (17 May 2013). A Catalogue of the Manuscripts of Christiaan Huygens including a concordance with his Oeuvres Complètes. BRILL. ISBN 9789004235656. Retrieved 12 April 2018.
- Audouin, Dollfus (2004). "Christiaan Huygens as telescope maker and planetary observer". In Karen, Fletcher (ed.). Titan – from discovery to encounter. Noordwijk, Netherlands: ESA Publications Division. pp. 115–132. Bibcode:2004ESASP1278..115D. ISBN 92-9092-997-9.
- Huygens, Christiaan (1977). Translated by Blackwell, Richard J. "Christiaan Huygens' The Motion of Colliding Bodies". Isis. 68 (4): 574–597. doi:10.1086/351876. JSTOR 230011.
- "Christiaan Huygens, Oeuvres complètes. Tome XXII. Supplément à la correspondance" (in Dutch). Digitale Bibliotheek Voor de Nederlandse Lettern. Retrieved 12 April 2018.
- Yoeder, Joella (1991). "Christiaan Huygens' Great Treasure" (PDF). Tractrix. 3: 1–13.
- Bell, A. E. (1947). Christian Huygens and the Development of Science in the Seventeenth Century. Edward Arnold & Co, London.CS1 maint: ref=harv (link)
- Daniel Garber (2003). The Cambridge History of Seventeenth-century Philosophy (2 vols.). Cambridge University Press. ISBN 978-0-521-53720-9. Retrieved 11 May 2013.
- Alan E. Shapiro (1973) Kinematic Optics: A Study of the Wave Theory of Light in the Seventeenth Century, Archive for History of Exact Sciences 11(2/3): 134–266 via Jstor
- Wiep van Bunge et al. (editors), The Dictionary of Seventeenth and Eighteenth-Century Dutch Philosophers (2003), Thoemmes Press (two volumes), article Huygens, Christiaan, p. 468–77.
- Andriesse, C.D., 2005, Huygens: The Man Behind the Principle. Foreword by Sally Miedema. Cambridge University Press.
- Boyer, C.B. (1968) A History of Mathematics, New York.
- Dijksterhuis, E. J. (1961) The Mechanization of the World Picture: Pythagoras to Newton
- Hooijmaijers, H. (2005) Telling time – Devices for time measurement in Museum Boerhaave – A Descriptive Catalogue, Leiden, Museum Boerhaave.
- Struik, D.J. (1948) A Concise History of Mathematics
- Van den Ende, H. et al. (2004) Huygens's Legacy, The golden age of the pendulum clock, Fromanteel Ltd, Castle Town, Isle of Man.
- Yoder, J G. (2005) "Book on the pendulum clock" in Ivor Grattan-Guinness, ed., Landmark Writings in Western Mathematics. Elsevier: 33–45.
- Christiaan Huygens (1629–1695) : Library of Congress Citations. Retrieved 30 March 2005.
|Wikimedia Commons has media related to Christiaan Huygens.|
|Wikiquote has quotations related to: Christiaan Huygens|
|Wikisource has the text of the 1911 Encyclopædia Britannica article Huygens, Christiaan.|
Primary sources, translations
- Works by Christiaan Huygens at Project Gutenberg:
- Works by or about Christiaan Huygens at Internet Archive
- Works by Christiaan Huygens at LibriVox (public domain audiobooks)
- Correspondence of Christiaan Huygens at Early Modern Letters Online
- De Ratiociniis in Ludo Aleae or The Value of all Chances in Games of Fortune, 1657 Christiaan Huygens' book on probability theory. An English translation published in 1714. Text pdf file.
- Horologium oscillatorium (German translation, pub. 1913) or Horologium oscillatorium (English translation by Ian Bruce) on the pendulum clock
- ΚΟΣΜΟΘΕΩΡΟΣ (Cosmotheoros). (English translation of Latin, pub. 1698; subtitled The celestial worlds discover'd: or, Conjectures concerning the inhabitants, plants and productions of the worlds in the planets.)
- C. Huygens (translated by Silvanus P. Thompson), Traité de la lumière or Treatise on light, London: Macmillan, 1912, archive.org/details/treatiseonlight031310mbp; New York: Dover, 1962; Project Gutenberg, 2005, gutenberg.org/ebooks/14725; Errata
- Systema Saturnium 1659 text a digital edition of Smithsonian Libraries
- On Centrifugal Force (1703)
- Huygens' work at WorldCat
- The Correspondence of Christiaan Huygens in EMLO
- Christiaan Huygens biography and achievements
- Portraits of Christiaan Huygens
- Huygens's books, in digital facsimile from the Linda Hall Library:
- Huygensmuseum Hofwijck in Voorburg, Netherlands, where Huygens lived and worked.
- Huygens Clocks exhibition from the Science Museum, London
- Online exhibition on Huygens in Leiden University Library (in Dutch)
- O'Connor, John J.; Robertson, Edmund F., "Christiaan Huygens", MacTutor History of Mathematics archive, University of St Andrews.
- Huygens and music theory Huygens–Fokker Foundation —on Huygens' 31 equal temperament and how it has been used
- Christiaan Huygens on the 25 Dutch Guilder banknote of the 1950s.
- Christiaan Huygens at the Mathematics Genealogy Project
- How to pronounce "Huygens" | 0.936922 | 3.452283 |
How old is the Earth?
Thanks to meteorites from space, rocks brought back by the Apollo astronauts from the Moon, and sundry other long-distance readings (mostly from satellites) taken of planetary bodies throughout the solar system, scientists have been able to calculate the age of the Earth. They believe the planets, including the Earth, formed between 4.54 to 4.58 billion years ago. In general, most scientists say that the Earth formed somewhere in between-about 4.55 to 4.56 billion years ago. (For more information about the Earth’s age, see “The Earth in Space.”)
The reason for the reliance on other space bodies to determine the Earth’s age is simple: The movement of the lithospheric plates around our planet has recycled and destroyed the Earth’s oldest rocks. If there are any primordial rocks left on Earth, they have yet to be discovered. Therefore, scientists must use other means to infer the age of our planet, including the absolute dating of planetary rocks that probably formed at the same time as the Earth.
What are some of the oldest rocks so far discovered on Earth?
Scientists have found rocks exceeding 3.5 billion years of age on all the Earth’s continents. But the oldest rocks uncovered so far are the Acasta Gneisses in north-western Canada near Creat Slave Lake, which has been dated at about 4.03 billion years old. Others that are not as old include the lsua Supracrustal rocks in West Greenland (3.7 to 3.8 billion years old), rocks from the Minnesota River Valley and northern Michigan (3.5 to 3.7 billion years old), rocks in Swaziland (3.4 to 3.5 billion years old), and rocks from western Australia (3.4 to 3.6 billion years old). These ancient rocks are mostly from lava flows and shallow water sedimentary processes. This seems to indicate that they were not from the original crust, but formed afterward.
The oldest materials found on Earth to date are tiny, single zircon crystals uncovered in younger sedimentary layers of rock. These crystals, found in western Australia, have been dated at 4.3 billion years old, but the source of the crystals has not yet been discovered. | 0.839223 | 3.207596 |
With the successful launch of the Falcon Heavy rocket to a (presumptive) Mars orbit, I found my thoughts going to the feasibility of space travel. Specifically, why we are massively limited in our ability to reach the stars. With our current technology, Mars may be about the limit of our reach. Why? Physics.
Let me preemptively caveat all of this by saying that I'm neither an engineer or physicist. Thus, when I create models, I take shortcuts in cases where I either don't know the answer or where the math proves too daunting. For example, calculating the amount of energy required to leave earth orbit depends on everything from air temperature to the location of the launch site (it takes less energy to launch from the equator, due to the spin of the earth. That's one of the reasons Cape Canaveral is located in Florida, I'd reckon). To simplify, I calculate based on acceleration from relative zero in the absence of gravity wells - this should consistently overestimate the speed/acceleration of the spacecraft in question. So when I show that something is pretty impossible, it's actually really impossible.
The Gas Problem
For all their ingenuity, SpaceX's launch technology is fairly primitive. It's what we've been using since the 1930s. Sure, there have been improvements in the aerodynamics, launch protocols, material sciences, etc., but every single spacecraft launched to date has essentially rode a barely-controlled, violent explosion into space. This is really inefficient (explosions are, after all, definitively the release of massive amounts of stored energy) and, at least equally importantly, mass intensive.
Let's use an example to illustrate how much gas it takes to go anywhere. Take the Falcon Heavy (for which I am drawing information here), the most advanced rocket on the planet. Imagine you want to go to the nearest star, Alpha Centauri. It's a short 4.22 light years. A puddle jump, in the scope of things. To make the trip, all we have to do is get to the speed of light and wait a few years (more than 4.22 years though; remember that we have to speed up and slow down to slower-than-light speed, but let's ignore that for the moment. I'm also ignoring time dilation, mainly because that's pushing the limits of my maths ability).
Imagine you wanted to make the trip in the Falcon Heavy. Let's also pretend you could survive the force of the thrust for as long as was required and that you could shrug off interstellar radiation and a hundred other things. How much fuel do you have to take with you?
I'll attach the math below, but here's the short, rough calculation: each booster rocket can produce 4.79 meters per second of acceleration. The Falcon Heavy has three, so it can accelerate 14.37 meters per second as long as the boosters are going (this is in the absence of gravity, a favorable situation for the hypothetical traveler)*.
How long to get to the speed of light? Easy math - divide light speed (300 million meters per second) by 14.37 and we find it'll take 241.6 days at full burn to get us up to light speed. That's a lot, but how much gas do we need in our spaceship to start with to burn for 241 days?
Per the internet sources on such things, the Falcon's engines effectively burn their entire fuel supply (a reported 1,187,100 kilograms) in about 162 seconds, so let's ballpark their consumption at 7,328 kg/sec. To burn the craft up to the speed of light, we'd need... let's see... 152,985,380,928 kilos of rocket fuel. That's 337 billion pounds, or about half the weight of earth's human population. I'm confident we don't have even one percent of this amount of rocket fuel on our planet.
Actually, I lied. This is only half the gas you need. Midway through the trip, the spacecraft must flip and begin burning its engines in the opposite direction to decelerate. Otherwise you're going to shoot right by your destination too fast to even see it. So you need 700 billion pounds of fuel.
My favorite of Newton's laws: Wherever you go, you leave something behind.
Those of you expecting me to have a solution to this problem in the next paragraph are in for a rough ride. In the world we live in, the Falcon's full primary burn is sufficient to accelerate the ship to a measly 0.00141% of the speed of light. That sucks. It's also why it takes us seven-ish months to get to Mars. Even within our solar system, the distance is so great that we have to wait until the orbital relationship between Mars and Earth is favorable for a short trip (this is called the Hohmann transfer window and, for Earth/Mars, is every 26 months). If it's this hard to get to the nearest planet, getting out of the solar system is impossible for a manned mission.
More efficient engines that require less mass. People have been fucking around with ion engines for a while. These are more efficient, but the force they generate is a tiny, tiny fraction of a percent of the force of the big, powerful (and I use that term relatively) rocket boosters. In other words, they're too slow. Renewable energy sources (via solar power) is another idea, but the sun becomes just another bright star in the sky when you get out there far enough. Same problem with heat energy from solar radiation.
Gravity boosts, where a spacecraft flies close enough to a planet to gain momentum from gravity, are another possibility. But let's put it in perspective: Voyager One used gravity assists from both Jupiter and Saturn and it still has just barely left the solar system some forty years later. They're only so powerful.
Point to point instantaneous travel via Einstein-Rosenthal bridge or other not-fully-understood phenomenon. Advantages: fast. Disadvantage: currently indistinguishable from magic. Possibly-to-probably theoretically impossible.
One of the really wonky solutions I've heard is a propulsion method called nuclear pulse propulsion. We detonate a nuclear device (hopefully in space!) and the spacecraft gains momentum on the force of the shockwave. Apparently the nuclear shockwave can be pretty powerful, even from a modest nuclear blast. Fun fact: the fastest man-made object ever recorded was a allegedly manhole cover ejected by a nuclear blast, which reached a speed of 150,000+ mph. Obviously, the force of the blast would turn the passengers into liquid goo, but then it becomes a materials question instead of a fuel issue, and I've always been a fan of flipping to a different set of problems when you're faced with an impossible situation.
Then there's the slow-and-steady idea: a colony ship capable of sustaining life indefinitely. But anyone who's ever been on a long car trip knows that there's no way a group of people locked up together in a 500-foot spacecraft for 200 years would not kill each other.
So, interstellar travel is about as impossible as walking between different casinos in Las Vegas during August. And none of these solutions solve any of the secondary issues I've mentioned in passing. Radiation tends to screw us up pretty badly. There's a lot of it outside earth's ionosphere and we're not very good at blocking it. And even if we had a perfect rocket engine that wouldn't melt after 240 days of spitting a fireball several football fields long, we'd still have to survive it - imagine enduring multiple Gs for years on end with no break.
I suspect there are other issues, but these are the ones that are the real limiters that I can think of off the top of my head. In order to get anywhere, we have to solve every single one of them. And that's why we're stuck on this rock, at least for the foreseeable future.
And now it seems like things are a little screwed up with even our modest reach for Mars. Maybe the Tesla roadster that Musk stuck in the rocket will come up with something.
*The Falcon has a second booster, but it's a little bitch engine compared to the first stage, so I ignored it. That's what you do for little bitch engines.
Noah's Inner Monologue
Scribblings of a man who can barely operate an idiotproof website. | 0.870559 | 3.751313 |
Crescent ♑ Capricorn
Moon phase on 15 November 2042 Saturday is Waxing Crescent, 2 days young Moon is in Sagittarius.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 2 days on 12 November 2042 at 20:28.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠23° of ♐ Sagittarius tropical zodiac sector.
Lunar disc appears visually 6.9% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1811" and ∠1940".
Next Full Moon is the Beaver Moon of November 2042 after 11 days on 27 November 2042 at 06:06.
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 2 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 530 of Meeus index or 1483 from Brown series.
Length of current 530 lunation is 29 days, 18 hours and 1 minute. It is 1 hour and 37 minutes longer than next lunation 531 length.
Length of current synodic month is 5 hours and 17 minutes longer than the mean length of synodic month, but it is still 1 hour and 46 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠201.7°. At the beginning of next synodic month true anomaly will be ∠232°. 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°).
4 days after point of apogee on 10 November 2042 at 12:15 in ♎ Libra. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 10 days, until it get to the point of next perigee on 25 November 2042 at 22:40 in ♉ Taurus.
Moon is 395 877 km (245 987 mi) away from Earth on this date. Moon moves closer next 10 days until perigee, when Earth-Moon distance will reach 359 651 km (223 477 mi).
5 days after its descending node on 10 November 2042 at 01:54 in ♎ Libra, the Moon is following the southern part of its orbit for the next 8 days, until it will cross the ecliptic from South to North in ascending node on 24 November 2042 at 01:03 in ♈ Aries.
18 days after beginning of current draconic month in ♈ Aries, the Moon is moving from the second to the final part of it.
13 days after previous North standstill on 1 November 2042 at 17:22 in ♊ Gemini, when Moon has reached northern declination of ∠28.455°. Next day the lunar orbit moves southward to face South declination of ∠-28.390° in the next southern standstill on 16 November 2042 at 08:09 in ♑ Capricorn.
After 11 days on 27 November 2042 at 06:06 in ♊ Gemini, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.149341 |
After a long 10 month journey to the red planet, a NASA spacecraft will enter Mars’s orbit on Sunday in order to investigate how the planet lost its water.
The spacecraft traveled 422 million miles from Earth and will experience a do-or-die burn of its braking rockets scheduled to start at 9:37 PM EDT/0137 GMT. MAVEN’s (Mars Atmosphere and Volatile Evolution) thruster burns will hopefully give the spacecraft enough speed to be captured by Mars’s gravity field and enter a looping orbit.
Starting Sunday, MAVEN will be going into an operational orbit after it maneuvers itself correctly and will come as close as 93 miles and as far away as 3,853 miles from the surface of the Red Planet. MAVEN’s mission is completely different from all other Mars orbiters, rovers and landers. The spacecraft is designed to analyze Mars’s atmosphere, suspected by scientists to have been much thicker in the past. Currently, it is comprised of mostly carbon dioxide gas.
According to scientists, in order for water to pool on the surface of the planet, denser air would be required and despite the fact that no water is present on its surface today, ancient river channels and lakebeds cover the Red Planet. There is also chemical evidence in support of this warmer, wetter past.
Bruce Jakosky, lead scientist in the MAVEN project, wants to find out where the water and the carbon dioxide from that early environment went. According to the University of Colorado scientist, there are only two possibilities: the water has either gone down in the crust of the planet or into the atmosphere, where the possibility exists of it being lost to space.
MAVEN’s mission will monitor what occurs when solar winds and charged particles come in contact with the upper layers of Mars’s atmosphere for one year. By doing so, scientists hope to understand the process involved and later on extrapolate back in time. At the end of their efforts, the MAVEN team wants to determine if Mars possessed the right conditions for life to have evolved.
Jakosky added that MAVEN will tell scientists about the “boundary conditions surrounding the potential for life on Mars.”
With MAVEN, the two U.S. orbiters, two U.S. rovers and one European orbiter will create a fleet working on revealing the secrets that the Red Planet holds. India has also sent out a Mars probe, its first, which should be arriving on Wednesday according to estimates. | 0.807222 | 3.155157 |
|Gravitational Wave Sources and Astrophysics||Numerical Relativity and Source Simulations||Data Analysis and Interpretation|
Matter in motion generates ripples that propagate in spacetime. Known as gravitational waves, these ripples travel out from the source, much like waves generated by a stone tossed into a pond. The forthcoming generation of ground and space-based gravitational wave detectors have unleashed exciting challenges and opportunities at the interface of general relativity, astrophysics, and experimental physics. The waves they will detect arise in strong, dynamical gravitational fields, offering the first opportunities to test our understanding of fully nonlinear relativistic gravity. Simultaneously, with the first detection, gravitational wave astronomy will open a new window to the Universe allowing astronomers to probe environments thus far inaccessible to conventional telescopes: e.g., the collision of black holes in the center of a galaxy at high redshift.
Research at the Center focuses on interdisciplinary problems at the interface of general relativity, gravitational waves, astrophysics and detector design. Click on each image above to learn more about research in these different areas. | 0.803887 | 3.396195 |
We might have just found an entirely new way of spotting aliens.
Scientists have proposed a new way of looking out for marks of aliens in the universe. And it could help us see life forms we’d completely miss otherwise.
Space agencies including Nasa have been active in launching new tools to study the universe, such as the James Webb Telescope. That will provide information on the atmospheric makeup of planets far away – but we might not be sure how to use that information.
Until now, scientists have mostly been looking for oxygen in the atmosphere. If that’s found, then it’s likely that there’s the chance for life on that planet, since we know from life on Earth that oxygen is key.
Nasa’s most stunning pictures of space
But we might be missing other important markers – known as biosignatures – that could indicate such worlds are supporting life. As such, planets might have life on them that we wouldn’t spot using just oxygen.
“This idea of looking for atmospheric oxygen as a biosignature has been around for a long time. And it’s a good strategy — it’s very hard to make much oxygen without life,” said Joshua Krissansen-Totton, an author on the paper published in Science Advances. “But we don’t want to put all our eggs in one basket. Even if life is common in the cosmos, we have no idea if it will be life that makes oxygen. The biochemistry of oxygen production is very complex and could be quite rare.”
To do the research, the scientists looked at the history of life on Earth, and the kinds of gases that were around when it was. They found that the planet had a complex mix of different gases, not only oxygen, and that looking for that cocktail could be a far more reliable marker of life on a planet.
“We need to look for fairly abundant methane and carbon dioxide on a world that has liquid water at its surface, and find an absence of carbon monoxide,” said co-author David Catling, a UW professor of Earth and space sciences. “Our study shows that this combination would be a compelling sign of life. What’s exciting is that our suggestion is doable, and may lead to the historic discovery of an extraterrestrial biosphere in the not-too-distant future.”
The scientists explored how a planet could have an imbalance of methane, including possible events like asteroid impacts or rocks interacting with water. But they found it would be very difficult to produce a lot of the gas on a rockey, Earth-like planet – unless it had living organisms on it.
The processes that generate both methane and carbon dioxide, such as big volcanic eruptions, would also tend to produce carbon monoxide alongside them. But carbon monoxide would be eaten up by microbes living on those planets.
“So if carbon monoxide were abundant, that would be a clue that perhaps you’re looking at a planet that doesn’t have biology,” said Mr Krissansen-Totton.
That means that if we were able to find methane and carbon dioxide on planets that didn’t have much carbon monoxide, it could be a good way of spotting aliens even at some distance away, they said.
The Independent’s bitcoin group is the best place to follow the latest discussions and developments in cryptocurrency. Join for the latest on how people are making money – and how they’re losing it. | 0.832102 | 3.629791 |
A sampling of recent articles, videos, and images from space-related science news items:
** ESA-led Heracles mission will return samples of the lunar surface to Earth: Landing on the Moon and returning home: Heracles – ESA
The Heracles lander will target a previously unexplored region near the lunar South Pole as an interesting area for researchers. A lander with a rover inside and ascent module on top will land there. Monitored and controlled from the lunar Gateway, the rover will scout the terrain in preparation for the future arrival of astronauts, and collect samples. The ascent module will take off from the surface and fly to the Gateway with the samples taken by the rover.
When the ascent module carrying the sample container arrives, the Gateway’s robotic arm will capture it and extract the sample container. The sample container will be received by the astronauts via a science airlock and pack it in NASA’s Orion spacecraft that is powered by the European Service Module. Orion will fly to Earth with astronauts and land with the Heracles lunar samples for analysis in the best laboratories on Earth.
** Massive metal deposit may underlie the Moon’s South Pole–Aitken basin: Mass Anomaly Detected Under the Moon’s Largest Crater – Baylor University
A mysterious large mass of material has been discovered beneath the largest crater in our solar system — the Moon’s South Pole-Aitken basin — and may contain metal from an asteroid that crashed into the Moon and formed the crater, according to a Baylor University study.
“Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground. That’s roughly how much unexpected mass we detected,” said lead author Peter B. James, Ph.D., assistant professor of planetary geophysics in Baylor’s College of Arts & Sciences.
The crater itself is oval-shaped, as wide as 2,000 kilometers — roughly the distance between Waco, Texas, and Washington, D.C. — and several miles deep. Despite its size, it cannot be seen from Earth because it is on the far side of the Moon.
Well, looks like my metal asteroid impact survivability theory just got a big boost… https://t.co/lfs3wYSaik
— Dennis Wingo (@wingod) June 10, 2019
Many other space scientists have claimed that the materials of such bodies were vaporized on impact and thinly spread over the Moon and thus not accessible by standard mining techniques.
** The Psyche mission will study a metallic asteroid up close : NASA’s Psyche Mission Has a Metal World in Its Sights – NASA
Designed to explore a metal asteroid that could be the heart of a planet, the Psyche mission is readying for a 2022 launch. After extensive review, NASA Headquarters in Washington has approved the mission to begin the final design and fabrication phase, otherwise known as Phase C. This is when the Psyche team finalizes the system design, develops detailed plans and procedures for the spacecraft and science mission, and completes both assembly and testing of the spacecraft and its subsystems.
“The Psyche team is not only elated that we have the go-ahead for Phase C, more importantly we are ready,” said Principal Investigator Lindy Elkins-Tanton of Arizona State University in Tempe. “With the transition into this new mission phase, we are one big step closer to uncovering the secrets of Psyche, a giant mysterious metallic asteroid, and that means the world to us.”
The mission still has three more phases to clear. Phase D, which will begin sometime in early 2021, includes final spacecraft assembly and testing, along with the August 2022 launch. Phase E, which begins soon after Psyche hits the vacuum of space, covers the mission’s deep-space operations and science collection. Finally, Phase F occurs after the mission has completed its science operations; it includes both decommissioning the spacecraft and archiving engineering and science data.
The Psyche spacecraft will arrive at Asteroid Psyche on Jan. 31, 2026, after flying by Mars in 2023.
The mission will also test laser communications with deep space probes:
** A review of the Hayabusa2 mission to the Ryugu asteroid, since its arrival in June of 2018: Treasure Hunting With Hayabusa2 – The Planetary Society
So far, multiple devices have been placed on the surface and an explosive was set off as well. A prime goal of the mission is to return a surface sample to Earth. One sampling was made in February.
As this article goes to press, we are deciding whether to collect a second sample from a region close to the crater or from a second site on the asteroid. This second sample will likely be our last since by July, Ryugu will be nearing the perihelion of its orbit, and its surface will become too warm for touchdown operations.
Hayabusa2 will then continue to examine Ryugu remotely until the end of the year and return to Earth with the samples at the end of 2020. It is going to be a busy few years!
This week the spacecraft made a “Low descent observation operation“, that is, it came in close and successfully dropped a target marker on the surface of the asteroid.
Preparations for the descent began on June 11 and the descent will begin on June 12 at 11:40 JST (on-board time) with the spacecraft descending at a speed of 0.4m/s. The speed will be reduced to 0.1 m/s at 22:00 JST on the same day. The spacecraft will read an altitude of about 35m on June 13 at 10:34 JST and then begin to ascend from 10:57 JST. The schedule of the operation is shown in Figure 1. Please be aware that the actual operation time may differ as the times shown are the planned values.
A view of Ryugu as the spacecraft closed in on it:
To make a model of Hayabusa2, check out the JAXA paper models page.
** An update on operational science spacecraft spread throughout the solar system: Where We Are: An At-A-Glance Spacecraft Locator | The Planetary Society
** Privately funded instrument on ESO’s VLT to search for near-by earth-like exoplanets: Breakthrough Watch and the European Southern Observatory achieve “first light” on upgraded planet-finding instrument to search for Earth-like planets in nearest star system | ESO
Newly-built planet-finding instrument installed on Very Large Telescope, Chile, begins 100-hour observation of nearby stars Alpha Centauri A and B, aiming to be first to directly image a habitable exoplanet
Breakthrough Watch, the global astronomical program looking for Earth-like planets around nearby stars, and the European Southern Observatory (ESO), Europe’s foremost intergovernmental astronomical organisation, today announced “first light” on a newly-built planet-finding instrument at ESO’s Very Large Telescope in the Atacama Desert, Chile.
The instrument, called NEAR (Near Earths in the AlphaCen Region), is designed to hunt for exoplanets in our neighbouring star system, Alpha Centauri, within the “habitable zones” of its two Sun-like stars, where water could potentially exist in liquid form. It has been developed over the last three years and was built in collaboration with the University of Uppsala in Sweden, the University of Liège in Belgium, the California Institute of Technology in the US, and Kampf Telescope Optics in Munich, Germany.
** Starshades would enable space telescopes to image earth-like exoplanets by masking out the light of their stars. NASA’s Starshade Technology Development program (ExEP) has come up with techniques for maintaining the extremely precise alignment needed between the starshade and the telescope, which will reside tens of thousands of kilometers apart: Starshade Would Take Formation Flying to Extremes | NASA.
“We can sense a change in the position of the starshade down to an inch, even over these huge distances,” Bottom said.
But detecting when the starshade is out of alignment is an entirely different proposition from actually keeping it aligned. To that end, Flinois and his colleagues developed a set of algorithms that use information provided by Bottom’s program to determine when the starshade thrusters should fire to nudge it back into position. The algorithms were created to autonomously keep the starshade aligned with the telescope for days at a time.
Combined with Bottom’s work, this shows that keeping the two spacecraft aligned is feasible using automated sensors and thruster controls. In fact, the work by Bottom and Flinois demonstrates that engineers could reasonably meet the alignment demands of an even larger starshade (in conjunction with a larger telescope), positioned up to 46,000 miles (74,000 kilometers) from the telescope.
A starshade project has not yet been approved for flight, but one could potentially join WFIRST in space in the late 2020s. Meeting the formation-flying requirement is just one step toward demonstrating that the project is feasible.
A demo of a starshade deployment:
** Hubble images a small galaxy “furiously forming” stars : Hubble Observes Tiny Galaxy with Big Heart | ESA/Hubble
Nestled within this field of bright foreground stars lies ESO 495-21, a tiny galaxy with a big heart. ESO 495-21 may be just 3000 light-years across, but that is not stopping the galaxy from furiously forming huge numbers of stars. It may also host a supermassive black hole; this is unusual for a galaxy of its size, and may provide intriguing hints as to how galaxies form and evolve.
** Mars 2020 rover includes instruments for detecting signs of life: Johnson-Built Device to Help Mars 2020 Rover Search for Signs of Life | NASA
Next summer, NASA is launching the Mars 2020 robotic rover to the Red Planet, loaded with equipment to search for signs that there once was life on Mars. One device, called the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) instrument, will be used to detect chemicals on the Martian surface that are linked to the existence of life. To keep the instrument working well, a team from the Astromaterials Research and Exploration Science (ARES) division at NASA’s Johnson Space Center (JSC) recently built a new calibration device for the rover to check SHERLOC’s function and properly tune it during the upcoming mission.
“SHERLOC is pretty complicated, and we came up with a list of 11 things that all have to be calibrated on this instrument,” said Marc Fries, ARES planetary scientist and Mars 2020 instrument co-investigator. “This sophisticated calibration device is also going to be used for a lot of other scientific and engineering investigations, and we’re really excited that it’s JSC’s contribution to the Mars 2020 rover.”
** And Mars 2020 rover instruments will help with human missions as well: NASA’s Mars 2020 Will Blaze a Trail – for Humans – NASA JPL
When a female astronaut first sets foot on the Moon in 2024, the historic moment will represent a step toward another NASA first: eventually putting humans on Mars. NASA’s latest robotic mission to the Red Planet, Mars 2020, aims to help future astronauts brave that inhospitable landscape.
While the science goal of the Mars 2020 rover is to look for signs of ancient life – it will be the first spacecraft to collect samples of the Martian surface, caching them in tubes that could be returned to Earth on a future mission – the vehicle also includes technology that paves the way for human exploration of Mars.
** More Mars exploration with Bob Zimmerman:
*** Ghost dunes on Mars – A “Star Trek Federation” logo feature is created by winds blowing on sand dunes:
Cool image time! The Mars Reconnaissance (MRO) science team today released a captioned image of several ghost dunes on Mars. The image [below] is cropped and reduced to highlight one of those ghosts, which the scientists explain as follows.
Long ago, there were large crescent-shaped (barchan) dunes that moved across this area, and at some point, there was an eruption. The lava flowed out over the plain and around the dunes, but not over them. The lava solidified, but these dunes still stuck up like islands. However, they were still just dunes, and the wind continued to blow. Eventually, the sand piles that were the dunes migrated away, leaving these “footprints” in the lava plain.
*** The Martian North Pole – A tour of the many weird features of the Martian north pole area:
Since the very beginning of telescopic astronomy, the Martian poles have fascinated. Their changing sizes as the seasons progressed suggested to the early astronomers that Mars might be similar to Earth. Since the advent of the space age we have learned that no, Mars is not similar to Earth, and that its poles only resemble Earth’s in a very superficial way.
Yet, understanding the geology and seasonal evolution of the Martian poles is critical to understanding the planet itself. | 0.908117 | 3.057287 |
C/2012 S1, Comet ISON, began in the Oort cloud, almost a light year away and has traveled for over a million years.
On Thanksgiving Day, Nov. 28, 2013, Comet ISON will sling shot around the sun - but what happens next is a mystery. Either it will break up due to the intense heat and gravity of the sun or it will speed back away, destination unknown, but certainly never to return.
C/2012 S1 was first spotted in September 2012, 585 million miles away. Scientists were instantly intrigued because, since this is ISON's very first trip into the inner solar system, it is still made of pristine matter from the earliest days of the solar system's formation. Its top layers haven't been lost by a trip near the sun.
To mark the journey, NASA has assembled a vast fleet of spacecraft and Earth-based telescopes to learn more about this time capsule from when the solar system first formed.
During the last week of its inbound trip, ISON will enter the fields of view of several NASA Heliophysics observatories. Comet ISON will be viewed first by the broad field of view seen by NASA's Heliospheric Imager instrument aboard its Solar Terrestrial Relations Observatory, or STEREO, Next the comet will be seen in what's called coronagraphs, images that block the brighter view of the sun itself in order to focus on the solar atmosphere, the corona.
Such images will come both from STEREO and the joint European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO. Then, NASA's Solar Dynamics Observatory, or SDO, will view the comet for a few hours during its closest approach to the sun, known as perihelion. The X-Ray Telescope on the JAXA/NASA Hinode mission will also be looking at Comet ISON for about 55 minutes during perihelion.
All of these observatories will have different views. STEREO-B will be the only one that sees the comet transit across the face of the sun. In SDO's view, the comet will appear to travel above the sun, and the SDO instruments will point away from the center of the sun to get a better view for three hours on Nov. 28. In addition to learning more about the comet itself, these observations can make use of the comet as a tracer to show movement in the solar wind and solar atmosphere.
The dates of viewings by these observatories are as follows:
- Nov 21-28: STEREO-A Heliospheric Imager
- Nov 26-29: STEREO-B coronagraphs
- Nov 27-30: SOHO coronagraphs
- Nov 28-29: STEREO-A coronagraphs
- Nov 28: SDO
- Nov 28: Hinode | 0.870847 | 3.746207 |
NASA-funded scientists have recently learned that cloud-to-ground lightning frequently strikes the ground in two or more places and that the chances of being struck are about 45 percent higher than what people commonly assume.
Recently, William C. Valine and E. Philip Krider in the Institute of Atmospheric Physics at the University of Arizona, co-authors of the study, took to the field using video and other technology to study lightning, which is one of the biggest weather-related killers in the United States, superseded only by extreme heat and flooding.
They recorded 386 cloud-to-ground (CG) lightning flashes on videotape during the summer of 1997 in Tucson, Arizona. They found that within their sample of 386 flashes, 136 flashes (35 percent) struck the ground in two or more places that were separated by tens of meters (yards) or more. There were a total of 558 different strike points; therefore, on average, each cloud-to-ground flash struck the ground in 1.45 places.
Rob Gutro | EurekAlert!
Upwards with the “bubble shuttle”: How sea floor microbes get involved with methane reduction in the water column
27.05.2020 | Leibniz-Institut für Ostseeforschung Warnemünde
An international team including scientists from MARUM discovered ongoing and future tropical diversity decline
26.05.2020 | MARUM - Zentrum für Marine Umweltwissenschaften an der Universität Bremen
In meningococci, the RNA-binding protein ProQ plays a major role. Together with RNA molecules, it regulates processes that are important for pathogenic properties of the bacteria.
Meningococci are bacteria that can cause life-threatening meningitis and sepsis. These pathogens use a small protein with a large impact: The RNA-binding...
An analysis of more than 200,000 spiral galaxies has revealed unexpected links between spin directions of galaxies, and the structure formed by these links...
Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.
Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...
In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".
Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...
Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.
researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...
19.05.2020 | Event News
07.04.2020 | Event News
06.04.2020 | Event News
04.06.2020 | Life Sciences
04.06.2020 | Physics and Astronomy
04.06.2020 | Life Sciences | 0.860921 | 3.376321 |
For a long time the Mars 2020 mission was just that — an unnamed mission to deliver a funky new rover to Mars that had been scheduled for liftoff this year. This is no longer a unnamed mission, with the new perseverance rover to land on Mars in 2021. Its launch is currently scheduled for a window from Jul 17 through to August 5. Its target is Mars’ Jezero Crater, and Perseverance is expected to touch down some time around February 18 2021.
The new rover’s mission is to look for signs of past microbial life and to study Mars’ climate and geology. Life. The search for something like us outside our own planet. This drives so much of our space exploration.
The new rover is the size of domestic sedan, weighing in around 1 metric tonne. Its design shows the ambitions for NASA’s whole Mars program, with Perseverance, managed by JPL, setup with a sophisticated drill, sampling arm, and sample storage setup that will tuck away soil samples for future return to Earth. Just think about that for a second. That is a game changer. The first planned two-way physical movement between our planetary birthplace and the Red Planet. This is only one part of a wider program, with a Lunar mission in 2024 and plans to maintain a continued human presence on the Moon from around 2028.
When we do eventually get our intrepid explorers to Mars, we will need to know the best place to land and set up a base of operations. One of the keys to this will be knowing where to get water — or in the case of conditions on Mars — water ice.
Recent research has indicated that water ice may be as little as 2.5 cm below the surface. All Martian astronauts should be issued with a portable spade!
There is a good reason water ice is under the surface. In the thin Martian atmosphere, even water ice located directly on the surface would evaporate, sublimating directly from solid to vapour.
One of the key considerations for success of any mission to Mars will be the strategic allocation of a wide range of resources. We will need to know exactly what we need to take with us, and exactly what we should expect to harvest from Mars’ surface and atmosphere. This includes not only water, but chemicals that could be used to make rocket fuels (check out Juggling Molecules on Mars, my prior post on Robert Zubrin’s Mars Direct concept).
One of the ways we can make this assessment of resources from Earth is by using orbiting satellites already in place around Mars. Two of these, which are proving invaluable, are NASA’s Mars Reconnaissance Orbiter (MRO) and the Mars Odyssey orbiter. Both of these have been used to locate Martian water ice potentially accessible to astronauts. Learning how to detect the presence of this water ice has meant piecing together data from multiple sources so that the temperature of the soil could be used as an indicator of the presence and depth of water. The calibration of the temperature-water relationship was achieved by synthesizing data from physical excavation near the poles by the Phoenix lander and data from studies of impact craters by MRO, where the ice has been exposed by asteroid impacts. The Thermal Emission Imaging System (THEMIS) camera on Mars Odyssey, and its Gamma Ray Spectrometer — designed for water detection — have all been crucial.
So where is the accessible water? At the poles and mid-latitudes.
Any landing will likely be in the northern hemisphere though, since the lower elevation means more atmosphere to cushion any landing. Perhaps in sites such as Arcadia Planitia, which shows promising ice deposits close to the surface.
These are preludes to human exploration of one our nearest solar system neighbours. One of our familiar, well-behaved, and unoccupied planets.
What happens when we reach our first exoplanet? What about one that is tidally locked to its star?
Check out what happens in my SF novel The Tau Ceti Diversion when they touch down to explore the first exoplanet.
With the crew dead, and the starship’s fusion drive held back from a lethal explosion, Karic and the surviving officers reach a habitable planet – the last thing they expected was to find it already occupied . . . | 0.860706 | 3.427496 |
The term “moonshot” is sometimes invoked to denote a project so outrageously ambitious that it can only be described by comparing it to the Apollo 11 mission to land the first human on the Moon. The Breakthrough Starshot Initiative transcends the moonshot descriptor because its purpose goes far beyond the Moon. The aptly-named project seeks to travel to the nearest stars.
The brainchild of Russian-born tech entrepreneur billionaire Yuri Milner, Breakthrough Starshot was announced in April 2016 at a press conference joined by renowned physicists including Stephen Hawking and Freeman Dyson. While still early, the current vision is that thousands of wafer-sized chips attached to large, silver lightsails will be placed into Earth orbit and accelerated by the pressure of an intense Earth-based laser hitting the lightsail.
After just two minutes of being driven by the laser, the spacecraft will be traveling at one-fifth the speed of light—a thousand times faster than any macroscopic object has ever achieved.
Each craft will coast for 20 years and collect scientific data about interstellar space. Upon reaching the planets near the Alpha Centauri star system, an the onboard digital camera will take high-resolution pictures and send these back to Earth, providing the first glimpse of our closest planetary neighbors. In addition to scientific knowledge, we may learn whether these planets are suitable for human colonization.
The team behind Breakthrough Starshot is as impressive as the technology. The board of directors includes Milner, Hawking, and Facebook co-founder Mark Zuckerberg. The executive director is S. Pete Worden, former director of NASA Ames Research Center. A number of prominent scientists, including Nobel and Breakthrough Laureates, are serving as advisors to the project, and Milner has promised $100 million of his own funds to begin work. He will encourage his colleagues to contribute $10 billion over the next several years for its completion.
While this endeavor may sound like science fiction, there are no known scientific obstacles to implementing it. This doesn’t mean it will happen tomorrow: for Starshot to be successful, a number of advances in technologies are necessary. The organizers and advising scientists are relying upon the exponential rate of advancement to make Starshot happen within 20 years.
Here are 11 key Starshot technologies and how they are expected to advance exponentially over the next two decades.
An exoplanet is a planet outside our Solar System. While the first scientific detection of an exoplanet was only in 1988, as of May, 1 2017 there have been 3,608 confirmed detections of exoplanets in 2,702 planetary systems. While some resemble those in our Solar System, many have fascinating and bizarre features, such as rings 200 times wider than Saturn’s.
The reason for this deluge of discoveries? A vast improvement in telescope technology.
Just 100 years ago the world’s largest telescope was the Hooker Telescope at 2.54 meters. Today, the European Southern Observatory’s Very Large Telescope consists of four large 8.2-meter diameter telescopes and is now the most productive ground-based facility in astronomy, with an average of over one peer-reviewed, published scientific paper per day.
Researchers use the VLT and a special instrument to look for rocky extrasolar planets in the habitable zone (allowing liquid water) of their host stars. In May 2016, researchers using the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile found not just one but seven Earth-sized exoplanets in the habitable zone.
Meanwhile, in space, NASA’s Kepler spacecraft is designed specifically for this purpose and has already identified over 2,000 exoplanets. The James Webb Space Telescope, to be launched in October, 2018, will offer unprecedented insight into whether exoplanets can support life. “If these planets have atmospheres, [JWST] will be the key to unlocking their secrets,” according to Doug Hudgins, Exoplanet Program Scientist at NASA headquarters in Washington.
The Starshot mothership will be launched aboard a rocket and release a thousand starships. The cost of transporting a payload using one-time-only rockets is immense, but private launch providers such as SpaceX and Blue Origin have recently demonstrated success in reusable rockets which are expected to substantially reduce the price. SpaceX has already reduced costs to around $60 million per Falcon 9 launch, and as the private space industry expands and reusable rockets become more common, this price is expected to drop even further.
Each 15-millimeter-wide Starchip must contain a vast array of sophisticated electronic devices, such as a navigation system, camera, communication laser, radioisotope battery, camera multiplexer, and camera interface. The expectation we’ll be able to compress an entire spaceship onto a small wafer is due to exponentially decreasing sensor and chip sizes.
The first computer chips in the 1960s contained a handful of transistors. Thanks to Moore’s Law, we can now squeeze billions of transistors onto each chip. The first digital camera weighed 8 pounds and took 0.01 megapixel images. Now, a digital camera sensor yields high-quality 12+ megapixel color images and fits in a smartphone—along with other sensors like GPS, accelerometer, and gyroscope. And we’re seeing this improvement bleed into space exploration with the advent of smaller satellites providing better data.
For Starshot to succeed, we will need the chip’s mass to be about 0.22 grams by 2030, but if the rate of improvement continues, projections suggest this is entirely possible.
The sail must be made of a material which is highly reflective (to gain maximum momentum from the laser), minimally absorbing (so that it is not incinerated from the heat), and also very light weight (allowing quick acceleration). These three criteria are extremely constrictive and there is at present no satisfactory material.
The required advances may come from artificial intelligence automating and accelerating materials discovery. Such automation has advanced to the point where machine learning techniques can “generate libraries of candidate materials by the tens of thousands,” allowing engineers to identify which ones are worth pursuing and testing for specific applications.
While the Starchip will use a tiny nuclear-powered radioisotope battery for its 24-year-plus journey, we will still need conventional chemical batteries for the lasers. The lasers will need to employ tremendous energy in a short span of time, meaning that the power must be stored in nearby batteries.
Battery storage has improved at 5-8% per year, though we often don’t notice this benefit because appliance power consumption has increased at a comparable rate resulting in a steady operating lifetime. If batteries continue to improve at this rate, in 20 years they should have 3 to 5 times their present capacity. Continued innovation is expected to be driven from Tesla-Solar City’s big investment in battery technology. The companies have already installed close to 55,000 batteries in Kauai to power a large portion of their infrastructure.
Thousands of high-powered lasers will be used to push the lightsail to extraordinary speeds.
Lasers have obeyed Moore’s Law at a nearly identical rate to integrated circuits, the cost-per-power ratio halving every 18 months. In particular, the last decade has seen a dramatic acceleration in power scaling of diode and fiber lasers, the former breaking through 10 kilowatts from a single mode fiber in 2010 and the 100-kilowatt barrier a few months later. In addition to the raw power, we will also need to make advances in combining phased array lasers.
Our ability to move quickly has…moved quickly. In 1804 the train was invented and soon thereafter produced the hitherto unheard of speed of 70 mph. The Helios 2 spacecraft eclipsed this record in 1976: at its fastest, Helios 2 was moving away from Earth at a speed of 356,040 km/h. Just 40 years later the New Horizons spacecraft achieved a heliocentric speed of almost 45 km/s or 100,000 miles per hour. Yet even at these speeds it would take a long, long time to reach Alpha Centauri at slightly more than four light years away.
While accelerating subatomic particles to nearly light speed is routine in particle accelerators, never before has this been achieved for macroscopic objects. Achieving 20% speed of light for Starshot would represent a 1000x speed increase for any human-built object.
Fundamental to computing is the ability to store information. Starshot depends on the continued decreasing cost and size of digital memory to include sufficient storage for its programs and the images taken of Alpha Centauri star system and its planets.
The cost of memory has decreased exponentially for decades: in 1970, a megabyte cost about one million dollars; it’s now about one-tenth of a cent. The size required for the storage has similarly decreased, from a 5-megabyte hard drive being loaded via forklift in 1956 to the current availability of 512-gigabyte USB sticks weighing a few grams.
Once the images are taken the Starchip will send the images back to Earth for processing.
Telecommunications has advanced rapidly since Alexander Graham Bell invented the telephone in 1876. The average internet speed in the US is currently about 11 megabits per second. The bandwidth and speed required for Starshot to send digital images over 4 light years—or 20 trillion miles—will require taking advantage in the latest telecommunications technology.
One promising technology is Li-Fi, a wireless approach which is 100 times faster than Wi-Fi. A second is via optical fibers which now boast 1.125 terabits per second. There are even efforts in quantum telecommunications which are not just ultrafast but completely secure.
The final step in the Starshot project is to analyze the data returning from the spacecraft. To do so we must take advantage of the exponential increase in computing power, benefiting from the trillion-fold increase in computing over the 60 years.
This dramatically decreasing cost of computing has now continued due largely to the presence of cloud computing. Extrapolating into the future and taking advantage of new types of processing, such as quantum computing, we should see another thousand-fold increase in power by the time data from Starshot returns. Such extreme processing power will allow us to perform sophisticated scientific modeling and analysis of our nearest neighboring star system.
Acknowledgements: The author would like to thank Pete Worden and Gregg Maryniak for suggestions and comments.
Image Credit: NASA/ESA/ESO | 0.911149 | 3.270535 |
Hubble Reveals a New Type of Planet
|GJ1214b, shown in this artist’s conception, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. New observations from NASA’s Hubble Space Telescope show that it is a waterworld enshrouded by a thick, steamy atmosphere. GJ1214b therefore represents a new type of world, like nothing seen in our solar system or any other planetary system currently known. Credit: David A. Aguilar (CfA)|
Our solar system contains three types of planets: rocky, terrestrial worlds (Mercury, Venus, Earth, and Mars), gas giants (Jupiter and Saturn), and ice giants (Uranus and Neptune). Planets orbiting distant stars come in an even wider variety, including lava worlds and “hot Jupiters.”
Observations by NASA’s Hubble Space Telescope have added a new type of planet to the mix. By analyzing the previously discovered world GJ 1214b, astronomer Zachory Berta (Harvard-Smithsonian Center for Astrophysics) and colleagues proved that it is a water world enshrouded by a thick, steamy atmosphere.
“GJ 1214b is like no planet we know of,” said Berta. “A huge fraction of its mass is made up of water.”
GJ 1214b was discovered in 2009 by the ground-based MEarth (pronounced “mirth”) Project, which is led by CfA’s David Charbonneau. This super-Earth is about 2.7 times Earth’s diameter and weighs almost 7 times as much. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.
In 2010, CfA scientist Jacob Bean and colleagues reported that they had measured the atmosphere of GJ 1214b, finding it likely that the atmosphere was composed mainly of water. However, their observations could also be explained by the presence of a world-wide haze in GJ 1214b’s atmosphere.
Berta and his co-authors used Hubble’s WFC3 instrument to study GJ 1214b when it crossed in front of its host star. During such a transit, the star’s light is filtered through the planet’s atmosphere, giving clues to the mix of gases.
“We’re using Hubble to measure the infrared color of sunset on this world,” explained Berta.
The super-Earth GJ 1214b, which has 6.5 times the mass of our Earth, orbits its star once every 38 hours at a distance of only 1.3 million miles. Astronomers estimate the planet¹s temperature to be about 400 degrees Fahrenheit. Although warm as an oven, it is still cooler than any other known transiting planet because it orbits a very dim star. Since GJ1214b crosses in front of its star, astronomers were able to measure its radius, which is about 2.7 times that of Earth. This makes GJ1214b one of the two smallest transiting worlds astronomers have discovered to date.
Credit: David A. Aguilar, CfA
Hazes are more transparent to infrared light than to visible light, so the Hubble observations help tell the difference between a steamy and a hazy atmosphere.
They found the spectrum of GJ 1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.
“The Hubble measurements really tip the balance in favor of a steamy atmosphere,” said Berta.
Since the planet’s mass and size are known, astronomers can calculate the density, which works out to about 2 grams per cubic centimeter. Water has a density of 1 g/cm3, while Earth’s average density is 5.5 g/cm3. This suggests that GJ 1214b has much more water than Earth, and much less rock.
As a result, the internal structure of GJ 1214b would be very different than our world.
“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’ — substances that are completely alien to our everyday experience,” said Berta.
Theorists expect that GJ 1214b formed farther out from its star, where water ice was plentiful, and migrated inward early in the system’s history. In the process, it would have passed through the star’s habitable zone. How long it lingered there is unknown.
GJ 1214b is located in the direction of the constellation Ophiuchus, and just 40 light-years from Earth. Therefore, it’s a prime candidate for study by the next-generation James Webb Space Telescope.
A paper reporting these results has been accepted for publication in The Astrophysical Journal and is available online: http://dx.doi.org/10.1088/0004-637X/747/1/35
This story has been translated into Portuguese. | 0.820657 | 3.846098 |
The number of confirmed exoplanets, or worlds orbiting distant suns, shot past 1,000 last week, according to the semi-official Extrasolar Planets Encyclopedia. That’s pretty heady stuff considering that just over 20 years ago we didn’t know of any at all. But the ultimate goal of finding a true Earthlike world has continued to elude astronomers.
That landmark discovery, however, appears to be closer than ever, particularly after the release of a pair of papers in the journal Nature this week, concerning a planet known as Kepler 78b. The new world is not only close to Earth in size (it’s just 20% bigger), but it has almost exactly the same density. The implication, says University of Hawaii astronomer Andrew Howard, lead author of one of the papers: “We think it’s made of the same stuff as Earth—primarily rock and iron.”
What makes this find truly compelling, however, is the very fact that there is not just one paper, but two. And that second one, based on independent observations from a European team, reaches exactly the same conclusion. “When results agree like this,” says Howard, “that’s really the gold standard.”
(MORE: Cloudy With a Chance of Aliens)
The planet was found earlier this year in data beamed down by the now-defunct Kepler satellite, but Kepler can tell scientist only how physically large an exoplanet is, based on what percentage of light it blocks as is it moves in front of its parent star. Before they began finding exoplanets in droves, theorists mostly assumed size and composition went hand in hand—that a planet in the size range of Jupiter, for example, must be like Jupiter in all respects.
Turns out they were wrong. Among the very first worlds discovered by Kepler, for example, one, Kepler 7b, is 50% bigger than Jupiter, but with the density of Styrofoam. Another, Kepler 10b is about the size of Earth but is nearly as dense as pure iron. Yet another, GJ 1214b (this one wasn’t found by Kepler), is less than three times the size of Earth, and has a density that suggests it’s probably half-rock and half-water. “There have been a lot of surprises,” Howard admits.
But it would have been downright astonishing if there were no true twins of Earth out there in the Milky Way, and both Howard’s team and the competing team, led by the University of Geneva’s Francesco Pepe, nailed down the composition of Kepler 78b with the same technique: the planet’s tug on its star as it orbits, pulling it almost imperceptibly in one direction and then the other. By measuring subtle changes in the star’s color induced by those wobbles, the astronomers can judge how fast the star moves as it approaches and retreats—and that speed depends on the planet’s mass.
It also depends on how tight the planet’s orbit is: the closer it is to the star, the more leverage it exerts. And Kepler 78b is crazy close—so close that its “year” last just 8.5 hours. “I mentioned this to a kid in my neighborhood,” says Howard, “and he said ‘wow, that would be great! I would have 10,000 birthdays already. That’s a lot of presents!’”
The simultaneous publication in Nature is not a coincidence. When the planet’s discovery was announced last spring, says Howard, his team asked the astronomers in Geneva to join them in a supporting role in measuring its mass. The Swiss liked the idea of a partnership—provided they were the ones taking the lead spot. “Neither of us wanted to play second fiddle to the other,” Howard says, “so we agreed to observe independently and submit our results to the same journal on the same day.”
Finding an Earth-size planet with an Earthlike composition is a major milestone in exoplanetology, but as a University of Maryland astronomer observes in a commentary, also published in Nature, the extra leverage—and close proximity to the parent star—that made the planet relatively easy to weigh “comes at the price of a hellish environment.” With a surface temperature of up to 8,500°F (4,700°C), says Howard, it’s “one of the hottest that’s ever been discovered.”
Kepler 78b is clearly not a place you’d expect to find life, in other words, and it may be that no current technology can discover such a planet. But a new space telescope called the Transiting Exoplanet Survey Satellite (TESS), coupled with powerful new wobble-measuring spectrographs on huge ground-based telescopes, could find a truly habitable Earthlike world. TESS won’t fly until 2017 at the earliest, but that’s nothing in cosmic time. If there’s a second Earth out there to be found, it’ll still be waiting when the new satellite opens its eyes.
(MORE: The Most Adorable Planet Yet) | 0.802294 | 3.821352 |
A wash of ice and rock from Halley’s comet provides the medium for this month’s Orionid meteor shower.
A sweep of debris from the celebrated Halley’s Comet will prick the night sky with fleeting lights this month as the Orionid meteor shower takes the celestial stage.
While the Orionid shower runs generally from early October to early November, it will peak this year on Monday and Tuesday with the best viewing times occurring in the dark hours before dawn.
A waning crescent moon will crash the show with some lunar light interruption, but the Orionids are known for leaving glowing trails that can last for several seconds to minutes, according to NASA.
During the peak of the shower, 10 to 20 Orionids per hour should be visible.
“The meteors in this shower are on the faint side, but they make up for that; maybe half of the Orionid meteors leave persistent trains, or ionized gas trails that last for a few seconds after the meteor itself has gone,” EarthSky editor in chief Deborah Byrd wrote in her column.
The Orionids are the only well-recognized major shower that happens twice a year. In May, the Earth again runs through the detritus of Halley’s Comet, creating the Eta Aquariid shower.
Halley’s Comet was discovered by Edmund Halley in 1705 but is believed to have been recognized for millennia. The comet returns about every 75 years and was last seen from Earth in 1986. It won’t come again until 2061.
The Orionids are named for the celestial hunter Orion, which is easy to spot in the night sky by its bright belt of three aligned stars. Orion is the namesake because the meteors appear to radiate from north of Betelgeuse, one of the constellation’s most well-known stars.
You don’t have to stare at Orion to see a meteor; they will be visible in all parts of the sky.
Although the moon may be slightly in the way during the peak of the shower, the weather forecast for Monday and Tuesday in South Florida is so far offering mostly clear skies with scattered rain chances.
AccuWeather is forecasting a “good” chance of seeing the Orionids for most of the Peninsula.
But North Florida has a slightly more iffy forecast. Although rain chances are low Sunday night into Monday morning, they pick up as a cool front approaches the area with mostly to partly- cloudy overnight skies.
The Panhandle, which may be dealing with tropical rainfall this weekend from an area of low pressure in the Gulf of Mexico, has only a 10 percent chance of rain Sunday night into Monday, but that picks up to 30 percent during the day through Tuesday. AccuWeather is giving “poor” to “fair” chances for Panhandle viewing.
Byrd said Halley’s Comet is “arguable the most famous of all comets.”
“Particles shed by the comet slam into our upper atmosphere, where they vaporize at some 60 miles above Earth’s surface,” she said. “Even one meteor can be a thrill.”
Florida’s coastal light pollution reduces the chances of seeing a metor, but a darkened beach is an option if a drive toward the Everglades isn’t.
“Bring along a blanket or lawn chair and lie back comfortably while gazing upward,” Byrd said.
CHECK the forecast for the Orionid meteor shower here.
This story originally published to palmbeachpost.com, and was shared to other Florida newspapers in the GateHouse Media network via the Florida Wire. The Florida Wire, which runs across digital, print and video platforms, curates and distributes Florida-focused stories. For more Florida stories, visit here, and to support local media throughout the state of Florida, consider subscribing to your local paper. | 0.822403 | 3.460129 |
Why Do the Positions of the Stars Change Each Month?
If you mark the locations of a set of stars one month, you won't see them in the same location the next. In fact, if you could measure positions precisely, you'd discover that stars appear to change locations each night. Although all other objects in the universe move through space, stellar motion does not account for large shifts in their positions each month.
Earth Makes Star Positions Change
As the planet rotates, the moon and stars appear to move across the sky just the way the sun does during the day. The Earth also revolves around the sun, causing different parts of the galaxy to appear during different points in the Earth's orbit. This means that if you view a group of stars one month, they'll appear in a different position one month later. During a complete revolution, which lasts one year, you will see all stars that are observable from your location on the planet.
Constellations Are Not Constant
Stars that you see at night belong to the Milky Way galaxy. The sun sits on one of the galaxy's arms and rotates around the center of the galaxy. Other stars in the galaxy follow their own orbits as well. This stellar motion causes constellations to change their shapes over time, but it takes a long time for people to see those changes. Astronomer Edmond Halley, for example, discovered that stars described in ancient Greek star charts had changed position slightly 1,600 years later. In about 50,000 years, the Big Dipper's shape will have changed so much that it won't look the same as it does today.
Although the Milky Way galaxy contains billions of stars, you can only see a few thousand of them with your naked eye. The best way to star-gaze is to travel to a location away from city lights. In addition to viewing stars, you can also see a few galaxies if you know where to look. While you need binoculars to view most of them, you can see the Andromeda galaxy with your naked eye. Like stars, it will also appear to change position each month as the Earth travels around the sun.
Interesting Astronomical Motion Facts
Nothing in the universe is stationary. Although you can’t see the sun, moon and stars moving, they are zooming along at incredible speeds. For instance, the sun and the solar system move at about 828,000 kilometers per hour (514,000 miles per hour). Even at that velocity, it takes about 230 million years for the solar system to complete a single rotation around the galactic center. You also can't tell that the Earth is rotating even though it spins about its axis at the equator at about 1,600 kilometers per hour (1,000 mph).
- Digital Vision./Photodisc/Getty Images | 0.81827 | 3.784357 |
Imaging of Earth from satellites in space has vastly improved in recent years. But the opposite challenge—using Earth-based systems to find, track and provide detailed characterization of satellites and other objects in high orbits—has frustrated engineers even as the need for space domain awareness has grown. State-of-the-art imagery of objects in low Earth orbit (LEO), up to 2,000 km (1,200 miles) high, can achieve resolution of 1 pixel for every 10 cm today, providing relatively crisp details. But image resolution for objects in geosynchronous Earth orbit (GEO), a favorite parking place for space assets roughly 36,000 km (22,000 miles) high, drops to just 1 pixel for every 2 meters, meaning many GEO satellites appear as little more than fuzzy blobs when viewed from Earth. Enabling LEO-quality images of objects in GEO would greatly enhance the nation’s ability to keep an eye on the military, civilian and commercial satellites on which society has come to depend, and to coordinate ground-based efforts to make repairs or correct malfunctions when they occur.
Achieving that goal will require radical technological advances because traditional or “monolithic” telescopes designed to provide high-resolution images of objects in GEO would be too physically and financially impractical to construct. For instance, achieving image resolution of 1 pixel to 10 cm for objects at GEO would require the equivalent of a primary imaging mirror 200 meters in diameter—longer than two football fields. To overcome these limitations and expedite the possible development of revolutionary benefits, DARPA has issued a Request for Information (RFI) (http://go.usa.gov/3Buvx) seeking specific technological information and innovative ideas demonstrating the potential for high-resolution imaging of GEO objects.
The RFI envisions a ground-based system that would be a sparse-aperture interferometer, which instead of relying upon one primary imaging mirror would measure the interference patterns of light detected by multiple smaller telescopes, from which a composite image could be derived. The GEO-imaging interferometer would rely on only passive (solar) illumination or thermal self-emission from imaged objects and could require the use of many telescopes, quite likely in a reconfigurable array. Responses to the RFI may inform a potential future program.
“We’re looking for ideas on how to create ground-based sparse aperture telescope systems that would provide GEO imagery as clear as current LEO imagery,” said Lindsay Millard, DARPA program manager. “This ‘100x zoom lens’ would provide the first ground-based capability to quickly assess anomalies that happen to GEO satellites, such as improperly deployed antennas or partially unfurled solar panels. With that capability, satellite owners could identify and fix problems more effectively and increase their satellites’ operating lifetimes and performance.”
“The image resolution this RFI envisions—down to a milli-arcsecond, or approximately one-3.6-millionth of a degree—would be up to 100 times more powerful than the current state of the art,” Millard continued. “Beyond helping us achieve our immediate needs on orbit, that improvement could significantly advance astronomy research, helping us learn about black holes and galaxy dynamics, as well as characterizing nearby exoplanets and detecting more-distant ones.”
The RFI invites short responses (3 pages or fewer) that explore some or all of the following technical areas:
To maximize the pool of innovative proposal concepts, DARPA strongly encourages participation by non-traditional performers, including small businesses, academic and research institutions and first-time government contractors. For this RFI, DARPA particularly seeks expertise in astronomy, novel optical design and quantum optics as it applies to long-baseline interferometry.
Responses are due Friday, July 3, 2015 to [email protected] by 4:00 PM Eastern Time. All technical and administrative correspondence and questions regarding this announcement and how to respond should be sent to [email protected].
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After reading this message, click to continue | 0.889708 | 3.299038 |
On 12 November 2014 Philae became the first spacecraft to land on a comet as part of the successful Rosetta mission to study Comet 67P/Churyumov-Gerasimenko. Five years later, and after the mission’s official end in 2016, Rosetta is continuing to provide insights into the origins of our Solar System.
Rosetta’s instruments have already discovered that the comet contained oxygen, organic molecules, noble gases and ’heavy’ or deuterated water different to that found on Earth.
As scientists continue to analyse data from Rosetta’s instruments, including the ionised gas or plasma, the results are improving our understanding of comets. Mission data is also being delivered to an archive as a future resource.
Rosetta orbits the Sun every 6.5 years and will pass the Earth again, visible from ground-based telescopes, in 2021. ESA’s future Comet Interceptor mission will build on Rosetta’s success when it performs a flyby of a comet. But, unlike Rosetta, the comet will be new to our Solar System.
The film contains interviews with Charlotte Goetz, Research Fellow, ESA; Kathrin Altwegg, ROSINA instrument principal investigator, Rosetta/University of Bern; Colin Snodgrass, Comet Interceptor deputy principal investigator/University of Edinburgh | 0.823396 | 3.275877 |
A new study from researchers at the California Institute of Technology (Caltech) suggests that Planet 9, the huge and so far unseen planet said to be lurking in the far reaches of the solar system, might be causing our group of planets to wobble a little and giving an impression that the sun is slightly tilted.
Elizabeth Bailey, lead author of the new study, points out the planets in our solar system orbit in a relatively flat plane with the sun.
But she says that plane rotates at a six-degree angle, making the sun look like its actually tilted.
She and her colleagues assert in their study that the enigmatic Planet Nine is so massive and has such a lopsided orbit compared to the other planets, that our solar system can’t help but slowly twist itself out of alignment.
Astronomers have long been puzzled by this tilt of the orbital plane, especially because of how the planets are said to have been formed.
The most popular theory among scientists is the ‘protoplanet hypothesis’ (pdf), which suggests the planets were eventually formed from a rotating cloud of gas and dust left over from the creation of the sun. Over time, gravity caused the cloud particles to gather and accumulate into objects such as planets.
“It’s such a deep-rooted mystery and so difficult to explain that people just don’t talk about it,” says Mike Brown, a Professor of Planetary Astronomy at Caltech in a press release.
Brown, along with his Caltech colleague Konstantin Batygin, caused quite a stir in the scientific community back in January after they uncovered evidence of the mysterious Planet 9.
The evidence of Planet 9 gathered by Brown and Batygin suggest that it has a mass that’s about 10 times more than Earth and 5,000 times that of Pluto.
It is also thought to orbit the sun from a distance of nearly 20 times farther than Neptune, whose average distance to the sun is about 4.5 billion kilometers.
They added that their mathematical modeling and computer simulations indicated that it would take Planet 9 between 10,000 and 20,000 years just to make one complete orbit around the sun.
Brown says that with the theorized size and distance of the giant mystery planet, the six degree tilt in the orbital plane fits perfectly, mathematically.
“It continues to amaze us; every time we look carefully we continue to find that Planet 9 explains something about the solar system that had long been a mystery,” says Batygin.
Astronomers continue to scan the skies in hopes of actually spotting and imaging Planet 9.
Video: Planet Nine Tilts the Sun! Q&A with Caltech Astronomers (Caltech) | 0.868005 | 3.69256 |
Information on this page is copyright R. N. Clark, all rights reserved.
This page is dedicated to amateur astronomy observing and discussions of how the eye operates in very faint light situations. The information is based on the my book and research I have done since publication of the book:
Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge University Press and Sky Publishing, (book of 355 pages), 1990. Copyright Roger N. Clark and Sky Publishing. This book is referred to as "Visual Astronomy" from here on.
Information may be freely used and printed for personal non-profit use by amateur astronomers for their pursuit of visual observing.
Optimum Magnified Visual Angle
In the book "Visual Astronomy," I derived a concept called the Optimum Magnified Visual Angle (OMVA). This is the angle to which an observer looking through a telescope can detect the faintest and lowest contrast objects. Using data from a World War II study to help soldiers see better at night, I interpreted the data from the perspective of viewing through a telescope. A long held concept in amateur astronomy observing is to increase the magnification of a telescope to "increase the contrast of the object being viewed." While the effect is real, the explanation is incorrect. As one changes magnification, all objects change size (e.g. object and sky background), so the contrast stays constant. But the eye's sensitivity to contrast changes as the object size changes, with lower contrast objects easier to detect when they appear larger, meaning at higher power.
As one magnifies an object in a telescope, the object appears larger, but its surface brightness (e.g. apparent magnitude per square arc-second) decreases. If the object is magnified too much, its surface brightness may be too faint to see. While some magnification can help viewing, too much hurts. So, there appears to be an optimum. I derived the optimum curve in "Visual Astronomy" and here I discuss the concept and the confusion that has surfaced since publication of the book.
Visual astronomical observations depend not just on detecting faint light but also on contrast discrimination. Both abilities are involved in seeing such things as spiral arms of galaxies and dark rifts in nebulae, and in simply perceiving any object against the sky background. Contrast detection thresholds, as a function of background surface brightness for several object diameters, are plotted in Figure 2.5 from "Visual Astronomy". This diagram shows that, for a given background (e.g. the night sky), less contrast is needed to see a larger object.
Figure 2.5 from Visual Astronomy. The minimum contrast needed to detect an object of a given angular size shown as a function of background surface brightness, do. The larger an object appears to the eye, the easier it is to detect. For small, bright objects on a bright background, a contrast less than 0.01 is enough for detection. But against the very dim night-sky background seen in a telescope (fainter than 25 magnitudes per square arc-sec), a large object must have a contrast of nearly 1.0, and a small object more than 100, to be detected. Derived from data in Table VIII of Blackwell (1946).
Critical Visual Angle
The data in Figure 2.5 were used to plot minimum detectable contrast versus angular size at constant values of background luminance to make Figure 2.6. Here we notice that for objects with small angular sizes, the smallest detectable contrast times the surface area is a constant. As an object becomes larger, this product is no longer constant. The angle at which the change occurs is called the critical visual angle. An object smaller than this angle is a point source as far as the eye is concerned. (A point can be considered the angular size smaller than which no detail can be seen.)
Figure 2.6 from Visual Astronomy. The smallest contrast needed to detect objects of various sizes on various backgrounds. This diagram is the most important one in the book, so it's worth taking the time to figure out its complexities. This is the same data as in Figure 2.5, except that contrast detection ability is plotted against angular size for various background surface brightnesses (magnitude per square arc-second).
When an object is magnified in a telescope, the contrast between object and background does not change since both are magnified equally. However, the object becomes larger as viewed by the eye. Therefore, moving horizontally across the chart corresponds to increasing the magnification.
As we start with low magnification on the left side, the contours of background surface brightness are diagonal straight lines. At a point called the critical visual angle, the lines begin to curve. Objects smaller than this value appear as point sources (the smallest detail that can be distinguished). As one moves to the right of the critical visual angle line, the faintest detectable surface brightness decreases faster than the background surface brightness. Thus, fainter objects--or detail within objects--can be seen as magnification is increased.
This is true only until the "optimum magnified visual angle" is reached. Thereafter, higher magnification decreases the detection threshold faster than surface brightness. A faint object is most visible when magnified to this angle. Derived from data in Table VIII of Blackwell (1946).
This critical angle is shown in Figure 2.7a plotted for various background luminances. Figure 2.7a shows that as the background becomes fainter, the size of a "point source" becomes larger for objects that are just detectable. In other words, the eye's resolution or ability to see detail is much coarser in the dark.
Figure 2.7a from Visual Astronomy. The eye's resolving power, unlike a camera's depends on an object's surface brightness. The critical visual angle is the angle below which no detail can be seen and objects appear as point sources.
Optimum Magnified Visual Angle
A low-contrast object is more easily detected if it is larger. For an extended object such as a galaxy viewed in a telescope, magnification does not change the contrast with the background, because both the sky's and the object's surface brightnesses are affected equally. Some visual observers have stated that a dim object's contrast with the sky background increases with higher magnification, but this is clearly wrong. The contrast merely looks greater because of the increased detection capabilities of the eye. Clark (1990) coined a name for the maximum magnification that will help detection: the "optimum magnified visual angle" (OMVA). This angle is shown in Figure 2.6 and also Figure 2.7b.
Figure 2.7b from Visual Astronomy. The "optimum magnified visual angle" of an object depends on surface brightness. This angle is the size for which a faint object, or detail within an object, should be magnified in order to maximize the possibility of detection.
If an object is at the threshold of detection and smaller
than the optimum angle, more magnification will make it easier to
see. When the object is magnified beyond the optimum angle, its
surface brightness decreases faster than the eye's contrast
detection threshold, and the object will become harder to
detect. Remember that even for an object somewhat above the
detection threshold, higher magnification may bring out details
within the object that are smaller than the optimum angle at a
There has been a fair amount of confusion, discussion and criticism over this concept. Here are some links:
an investigation into the visual Optimum Detection Magnification, by Mel Bartels
Another interpretation of the data from Blackwell, H R (1946): Contrast Thresholds of the Human Eye by Nils Olof Carlin
In a long public and private email series among the above authors, we tried to understand each others points and to try and figure out what is correct (this was not simple). These discussions ended without full resolution of the issues. However, we did learn a few things.
First, two general methods were being used to derive the OMVA.
I derived the original OMVA by hand methods in the early 1980s before I had the modern computer tools, but using method 2 above. Nils Olof Carlin and I generally used method 2 and the Mel Bartels page above uses method 1. In our long discussions, and on the pages above, the other authors have yet to derive a new OMVA curve.
Some of the disagreement centered on my saying the OMVA occurs at a slope of -1 on the curves of constant surface brightness in Figure 2.6. Derivations by others in our discussions came out with a slope of -2. But I think people are solving different problems (e.g. the method 1 above). Methods which change contrast while changing magnification in a telescope are incorrect in my view, because the contrast of extended objects does not change when you change magnification in a telescope. This fact, I believe, is the root cause of much of the confusion.
When one magnifies an object in a telescope, one moves horizontally across the Figure 2.6 diagram. The object gets larger proportional to the magnification, m, but the surface brightness decreases in proportion to 1/m2. So it is the horizontal spacing of the surface brightness curves in Figure 2.6 that controls where the optimum is located. If the slope is steeper than -1 on the Figure, increasing magnification helps detection. As the slope of the surface brightness curves becomes more horizontal, the spacing stretches out (in constant contrast, or horizontally) and one loses detection ability due to loss in surface brightness faster than one gains by increasing the apparent size. This trade point occurs at a slope of -1. This is the optimum. On this point, at least some of the others (above) probably still disagree. Perhaps after reading this page, we can collectively go over the data, including the new data I present below, and derive a better solution.
Regardless of where the correct optimum is, the data I present below shows the optimum is a shallow function, and if you follow the advice in the very last paragraph, you will observe all detail close enough to the optimum that this academic disagreement is meaningless in practice.
One thing that came of our discussions, the Optimum Detection Magnifications in Appendix F of Visual Astronomy (in which I used method 1 in a way I didn't realize until these discussions) is wrong. Do not use it! The program I wrote changes contrast and thus is flawed.
However, the "Minimum Optimum Detection Magnification" (MDM) in Appendix E is still correct to the best of my knowledge.
So what does all this mean?
What few people realize is that the data presented in Figure 2.5 and 2.6 are projections of a 3-dimensional surface onto 2-dimensional graphs. The 3-D surface is shown below in Figure A.
Figure A. The "Blackwell Surface" for threshold detection. Detection of a faint object by a visual observer depends on 3 things: 1) surface brightness of the object, 2) the object's angular size, and 3) the contrast with the background. An object is detectable if it plots on the surface or above it.
Figure 2.5 is the projection of Figure A to the upper left plane. Figure 2.6 is the projection of the data onto the upper right plane. The third projection is the floor and is shown below in Figure B.
Figure B. The threshold contrast as a function of apparent angular size and surface brightness. The curves on the plot are constant contrast. The red diagonal lines represent the magnification trend in a telescope. The optimum magnified visual angle (OMVA) occurs tangent to a contrast curve. The white line shows my new derivation of the OMVA, first presented at the May 2001 Riverside Telescope Makers Convention (RTMC). The idea for this derivation was first presented to me by _______ of England in 19__ (I'm searching for this letter).
The OMVA in Figure B shows a second way to look at the Blackwell data and derive the OMVA. As one can see from the tangent points, and considering the data have been re-interpolated a couple of times, one might wonder how accurate the derivation of and OMVA is. Let's look at another way to check what the OMVA is.
The Minimum Aperture Needed to Detect M57 as a Ring
A simple method to check the OMVA is actual observations of simple deep-sky objects. An excellent object is M57. What is the minimum aperture needed to detect the ring nature of the object as a function of magnification? For this test, I did it in one night when the object was overhead and used aperture masks, so variations in sky conditions was minimal and telescope transmission was a constant. The results are shown in Figures C and D.
Figure C. The minimum aperture needed to detect the ring nature of M57 at various magnifications. The curve shows the "barely" to "easy" apertures as the bottom and top curves, respectively. The average of the barely and easy is shown as the heavy line. The image is an M57 drawing using my 12.5-inch telescope and many magnifications.
The central hole is about 3/4 arc-minute across. The minimum aperture occurs at a magnification of about 130x (+/- 30), which means the optimum diameter occurs at about 100 arc-minutes as viewed by your eye. The background surface brightness is about 25.5 magnitudes /square arc-second (including 0.4 mag/sq. arc-sec. for transmission loss in the telescope).
Figure D. The mean surface brightness of M57 as a function of magnification when it is just detectable at each aperture in Figure C.
Note how shallow the minimum is in the M57 ring detection experiment in Figure C. The OMVA is not a precise value.
Now let's try and determine the OMVA at the brighter surface brightnesses. Click on the figure below to see a test chart of low contrast spots of various sizes.
If you print this chart at 300 dpi, and hold it at 30 inches from your eye, the 27 pixel diameter spots appear about 10.3 arc-minutes across. Viewing the chart in low room light gets near the right side of Figure 2.7b. For the low contrast spots, how large do they have to be to be seen (just above the threshold)? I tried some various lighting conditions and found a range of about 6 to 13 arc-minutes were needed to detect the low contrast spots (e.g. the 2 DN brighter than the background). I did the experiment before computing the spot sizes so I did not know what the outcome would be.
Plotting the M57 point, the low contrast spot experiment, along with OMVA from Figure 2.6 and Figure B, we see the result in Figure E, below.
Figure E. OMVA from Figure 2.6 and Figure B and the derived point from the M57 experiment.
The new Optimum Magnified Visual Angle (OMVA) curve (Figure E, red line) is much more complex than the original OMVA curve (Figure E, black line). However, both indicate a general upward trend of increasing apparent angular size with decreasing surface brightness. Which is correct? It appears that the original OMVA agrees with observational data so far, but more precise data are needed to be sure. I do not think the OMVA data are good enough with the interpolations that have been done (starting with Blackwell, 1946). It is clear that the OMVA has a broad minimum. It is also clear that the OMVA for very faint objects is on the order of 0.5 to 1.5 degrees (it may be more than about 100 arc-minutes at the faint end).
Thus, the observing strategy to detect deep-sky objects, or detail within objects, is to magnify those objects, or detail within the objects. so they appear about 100 arc-minutes in size. For example, if you are trying to detect a dark nebula in a galaxy arm, magnify that dark nebula so that it appears about a degree across or more.
What Does All This Mean?
To see all the detail in an object, use many powers, from very low to very high, examining the entire object with each magnification. Because the OMVA appears to be a shallow minimum, one need not be precisely on the optimum. Within a factor of 2 or a little less in magnification is fine. A magnification sequence of: 35x, 50x, 80x, 120x, 180x, 270x, 400x ... (a sequence increasing magnification by a factor of about 1.5) is great.
Blackwell, R.H., Contrast Thresholds of the Human Eye, Journal of the Optical Society of America, v36, p624-643, 1946.
Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge University Press and Sky Publishing, 355pp., 1990.
Clarkvision Visual Astronomy Main Page
This page URL:
First published February, 2002.
Last Modified December 18, 2007 | 0.80256 | 3.796252 |
I have seen the future of space exploration, and it looks like a cue ball covered with brown scribbles. I am talking about Europa, the 1,940-mile-wide, nearly white, and exceedingly smooth satellite of Jupiter. It is an enigmatic world that is, in many ways, almost a perfect inversion of Earth. It is also one of the most plausible places to look for alien life. If it strikes you that those two statements sound rather contradictory—why yes, they do. And therein lies the reason why Europa just might be the most important world in the solar system right now. The Europa Clipper spacecraft is scheduled to launch in 2023 to probe the mysterious moon, according to NASA’s 2020 budget proposal.
The unearthly aspects of Europa are literally un-earthly : This is an orb sculpted from water ice, not from rock. It has ice tectonics in place of shifting continents, salty ocean in place of mantle, and vapor plumes in place of volcanoes. The surface scribbles may be dirty ocean material that leaked up through the icy equivalent of an earthquake fault.
From a terrestrial perspective, Europa is built all wrong, with its solid crust up top and water down below. From the perspective of alien life, though, that might be a perfectly dandy arrangement. Beneath its frozen crust, Europa holds twice as much liquid water as exists in all of our planet’s oceans combined. Astrobiologists typically flag water as life’s number-one requirement; well, Europa is drowning in it. Just below the ice line, conditions might resemble the environment on the underside of Antarctic ice sheets. At the bottom of its buried ocean, Europa may have an active system of hydrothermal vents. Both of these are vibrant habitats on Earth.
Icy material tends to boil off, producing an exotic kind of weathering that rearranges the landscape without any wind or rain.
Adding a new twist to the story, Europa’s water may sometimes escape its icy confines. On at least four occasions, the Hubble Space Telescope has detected what appear to be large plumes of water vapor erupting from Europa. That detection has confirmed and expanded on the scientific ideas about what makes Europa such a dynamic world. Europa travels in a slightly oval orbit around Jupiter, causing it to get alternately squeezed and stretched by the giant planet’s gravity. The flexing creates intense friction inside the satellite and generates enough heat to maintain a warm ocean beneath Europa’s frozen outer shell. The presence of a plume suggests that the stretching of Europa also opens and closes a network of fissures that allow buried water to erupt as geysers.
If the geysers consist of ocean water shooting all the way through the crust, they could carry traces of aquatic life with them. And if the plumes rise high enough, a future spacecraft could fly right through them, sniffing for biochemicals.
You can see why people were giddy at a 2015 OPAG meeting held at NASA’s Ames Research Center. A regular forum for geeking out about ice worlds, the OPAG gatherings—short for Outer Planet Assessment Group—feel halfway between the corporate swarm of a MacWorld expo and a vinyl record fair. They are where true believers mingle with the newbies, showing off the latest science, kicking around speculative ideas, and developing strategies for exploration. With each new bit of data, they have grown increasingly convinced that Europa, not Mars, is the place to go to search for alien life. Finding the plume on Europa was another shot of adrenaline. The room went fervently silent as Lorenz Roth of Sweden’s Royal Institute of Technology, calling in via a fuzzy phone line, reported on the latest search for a recurrence of such water eruptions (no luck yet, alas).
Another significant piece of news was hanging over the OPAG meeting: The discovery that Europa has plate tectonics, like Earth and unlike any other world we know of. Tectonics describes a process in which the crust moves about and cycles back and forth into the interior. Louise Prockter of Johns Hopkins University’s Applied Physics Laboratory co-discovered this style of activity on Europa by painstakingly reconstructing old images from the Galileo spacecraft, which circled Jupiter from 1995 to 2003. (Analysis of other Galileo data suggests the probe flew right past a Europan water plume in 1997, but scientists didn’t realize it at the time.)
As Prockter explained to me at the meeting, a mobile crust potentially does two important things. It cycles surface ice, along with all the compounds it develops during exposure to the sun, down into the dark ocean; that chemical flow could be crucial for supplying the ocean with nutrients. The motion of the crust also brings ocean material up to the surface, where prying human eyes can seek clues about the Europan ocean without actually drilling down into it.
Bolstered by these discoveries, the cult of Europa has now escaped the confines of the OPAG meetings. A successful mission to Europa would bring into focus the incredible ice-and-ocean environment of Europa. It would also help scientists understand ice worlds in general. Icy moons, dwarf planets, and giant asteroids are the norm in the vast outer zone of the solar system, and if they repeat the pattern of Europa they may contain much of the solar system’s habitable real estate. There is good reason to think that ice worlds are similarly abundant around other stars as well. Putting all of these new ideas together suggests that the Milky Way may collectively contain tens of billions of life-friendly iceboxes.
But if these stunning extrapolations seem to suggest that scientists are starting to get a handle on how Europa works, allow me to suggest otherwise. Europa is still largely a big, icy ball of confusion.
A lmost everything we know about the surface of Europa comes from NASA’s Galileo mission, which reached Jupiter in 1995. During its eight-year mission, Galileo mapped most of Europa, but at a crude resolution of about one mile per pixel. For comparison, today’s best Mars images show features as small as three feet. Elizabeth “Zibi” Turtle of the Hopkins Applied Physics Lab promises that the camera on NASA’s upcoming Europa probe will achieve a similar level of clarity. Until then, imagine trying to navigate using a map that doesn’t show anything smaller than one mile and you will get a sense of how far the Europa scientists have to go.
What’s more, at a very basic level, planetary scientists still do not have a good handle on how geology (or maybe we should say “glaciology?”) works in frozen settings. Ice, you see, is not just ice. Robert Pappalardo of NASA’s Jet Propulsion Laboratory, the ponytail-wielding mission scientist for the agency’s upcoming Europa probe, spelled out some of the complexities to me. On Europa, surface temperatures on a warm day at the equator might rise up to -210 degrees Fahrenheit; at the poles, the lows plunge to -370 degrees Fahrenheit. Under those conditions, water is properly thought of as a mineral, and ice has approximately the consistency of concrete. In many ways it is remarkably similar to rock in how it fractures, faults, and shatters. But even in such a deep freeze, surface ice can sublimate—evaporate directly from solid to gas—in a way that rock does not. Icy material tends to boil off from darker, warmer regions and collect on lighter, cooler ones, producing an exotic kind of weathering that rearranges the landscape without any wind or rain.
All sorts of other things are happening on the surface of Europa. Jupiter has a huge, potent magnetic field that bombards its satellite with radiation: about 500 rem per day on average, which you can more easily judge as a dose strong enough to make you sick in one hour and to kill you in 24. That radiation quickly breaks down any organic compounds, greatly complicating the search for life, but produces all kinds of other complex chemistry. A lab experiment at the Jet Propulsion Laboratory suggests that the colors of Europa’s streaks are produced by irradiated ocean salts. These and other fragmented molecules, along with a steady rain of organic material delivered by comet impacts, could be used as energy sources for life when they circulate back down into the ocean, where any living things would be well protected.
If an alien swims in Europa’s ocean and nobody is able to see it, is it really alive?
The movement of Europa’s crust—its icy outer shell—is another broad area of mystery. On ice worlds, Pappalardo notes, water takes on the role of magma and hot rock deep below the surface, but once again ice and rock are not quite the same. Warm ice turns soft, almost slushy, under high pressure and slowly flows. There could be complicated circulation patterns contained entirely within the crust, which is perhaps 10 to 15 miles thick (or maybe more or less; that is yet another mystery that the Europa mission will investigate). Pools of liquid water might exist trapped within the shell, cut off from the underlying ocean. Plumes of water at the surface might not originate directly from the ocean; it is possible that they come from these intermediate lakes, analogous to the largely unexplored Lake Vostok in Antarctica.
At the OPAG meeting, seemingly narrow arguments about the circulation of ice sparked colorful debates about prospects for life on Europa and, by extension, on the myriad other ice worlds out there. Britney Schmidt of Georgia Tech wondered if the active geology (glaciology) on Europa occurs entirely within the crust. If material does not circulate at all between surface and ocean, Europa is sealed tight. Life could not get any fresh chemicals from up above, and if it somehow manages to survive anyway we might never know unless we find a way to dig a hole all the way through. Several researchers at OPAG suggested that meaningful answers will require a surface lander; one energetic audience member repeatedly argued for sending an impactor—a high-speed bowling ball, essentially—to smack the surface and shake loose any possible buried microbes.
As for the Europan ocean itself, that runs even deeper into what you might call aqua incognita . If the surface truly is streaked with salts, as the recent experiments indicate, that suggests a mineral-rich ocean in which waters interact vigorously with a rocky seafloor at the bottom. A likely source of such interaction is a network of hydrothermal vents powered by Europa’s internal heat; such vents could provide chemical energy to sustain Europan life, as they do on Earth. But how much total hydrothermal activity goes on? Are the acidity and salinity conducive to life? How much organic material is down there? The scientists egged each other on with provocative questions that, as yet, have no answers.
When (or if) we will find out will depend, in large part, on how much of Europa’s inner nature is evident from the outside. The conversations at OPAG sometimes devolved into something resembling a college existential argument: If an alien swims in Europa’s ocean and nobody is able to see it, is it really alive?
T he Europa faithful have been waiting a long time for a mission that would wipe away those kinds of arguments, or at least ground them in hard data. That wait has been full of whipsaw swings between optimism and disappointment. NASA’s planned Europa Orbiter got a green light in 1999, only to be cancelled in 2002. The agency rebounded with a proposal for an even more ambitious, nuclear-propelled Jupiter Icy Moons Orbiter, which looked incredible until it got delayed and finally cancelled in 2006. A proposed joint venture with the European Space Agency never even got that far, though the Europeans are going ahead with their part of the project, which will send a probe to Ganymede, another one of Jupiter’s icy moons, in 2030.
The Europa Clipper, outfitted with scientific instruments that include cameras and spectrometers, will swoop repeatedly past the moon and produce images that determine its composition. There is a chance the Europa mission will include a lander. Funding does not exist yet, but Adam Steltzner—the hearty engineer who figured out how to land the two-ton Curiosity rover safely on Mars—assures me that from a technical standpoint it would not be difficult to design a small probe equipped with rockets to allow a soft touchdown on Europa. There it could drill into the surface and search for possible organic material that has not been degraded by the radiation blasts from Jupiter.
What you won’t see, the OPAG boffins all sadly agreed, is one of those cool Europa submarines that show up on the speculative “future mission concept” NASA web pages. Getting a probe into Lake Vostok right here on Earth has proven a daunting challenge. Drilling through 10 miles or more of Europan ice and exploring an alien ocean by remote control is something we still don’t know how to do, and certainly not with any plausible future NASA budget.
No matter. Even the no-frills version of NASA’s current Europa plan will unleash a flood of information about how ice worlds work, and about how likely they are to support life. If the answers are as exciting as many scientists hope—and as I strongly expect—it will bolster the case for future missions to Titan, Enceladus, and some of Europa’s other beckoning cousins. It will reshape the search for habitable worlds around other stars as well. Right now astronomers are mostly focused on finding other Earthlike planets, but maybe that is not where most of the action is. Perhaps most of the life in the universe is locked away, safe but almost undetectable, beneath shells of ice.
Whether or not Europa is home to alien organisms, it will tell us about the range of what life can be, and where it can be. That one icy moon will help cure science of its rocky-planet chauvinism. Hey, who you calling cue ball?
Corey S. Powell is a contributing editor at American Scientist and at Discover, where he writes the Out There blog. He is also the co-host of the upcoming Science Rules podcast. He tweets actively about all things space and astronomy: @coreyspowell
The lead image is courtesy of Wikipedia.
A slightly different version of this article was originally published in our “Water” issue in June, 2015. | 0.889062 | 3.793863 |
On 4 July, NASA intends to finish a job that started with the agency’s Galileo mission 21 years ago. At 8:18 p.m. Pacific time, the Juno spacecraft will ignite its main engine for 35 minutes and nudge itself into orbit around Jupiter. If all goes well, it will eventually slip into an even tighter path that whizzes as close as 4,200 kilometres above the planet’s roiling cloud-tops — while dodging as much of the lethal radiation in the planet’s belts as possible.
The US$1.1-billion mission, which launched in 2011, will be the first to visit the Solar System’s biggest planet since NASA’s Galileo spacecraft in 1995. Picking up where Galileo left off, Juno is designed to answer basic questions about Jupiter, including what its water content is, whether it has a core and what is happening at its rarely seen poles (see ‘Mission to Jupiter’).
Scientists think that Jupiter was the first planet to condense out of the gases that swirled around the newborn Sun 4.6 billion years ago. As such, it is made up of some of the most primordial material in the Solar System. Scientists know that it consists mostly of hydrogen and helium, but they are eager to pin down the exact amounts of other elements found on the planet.
“What we really want is the recipe,” says Scott Bolton, the mission’s principal investigator and a planetary scientist at the Southwest Research Institute in San Antonio, Texas.
A murky disposition
Jupiter’s familiar visage, with its broad brown belts and striking Great Red Spot, represents only the tops of its churning clouds of ammonia and hydrogen sulfide. Juno — named after the Roman goddess who could see through clouds — will peer hundreds of kilometres into the planet’s atmosphere using microwave wavelengths.
Exploration of Jupiter’s interior should reveal more about the formidable atmospheric convection that powers the planet, says Paul Steffes, an electrical engineer at the Georgia Institute of Technology in Atlanta.
Steffes and his colleagues have run a series of laboratory experiments to simulate what different layers of Jupiter’s atmosphere might look like: from near the cloud-tops, where experimental temperatures are –100 °Cto deeper in the planet, where they rise to more than 300 °C.
By comparing Juno’s observations to their simulations, the scientists hope to determine how much ammonia, water vapour and other materials swirl at different atmospheric depths. “Once we understand the recipe for Jupiter’s atmosphere, we’ll get a clearer insight into how it evolved,” says Steffes. Different theories predict varying amounts of water in Jupiter’s atmosphere, depending on whether the planet coalesced at its current distance from the Sun or somewhere else. Actual measurements of atmospheric water content could help to clarify this debate.
Normal is good
In anticipation of Juno’s arrival, professional and amateur astronomers have been observing Jupiter with ground-based and space-based telescopes. For now, the planet is not experiencing any unusual atmospheric changes. “It’s kind of in its normal state, which is good,” says Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. This ‘normal’ behaviour gives researchers confidence that they will be able to understand Juno’s findings.
The Great Red Spot continues to shrink, as it has done in recent years, and to interact less and less with the jet streams on either of its edges. The broad belt just north of the planet’s equator has been expanding since late 2015 — a change that might be connected to processes deep in the atmosphere.
“Trying to connect events that are happening at one level to events happening in another tells you how well coupled the whole atmosphere is,” says Leigh Fletcher, a planetary astronomer at the University of Leicester, UK.
As Juno probes deeper and deeper into the planet’s atmosphere, researchers hope to get information on a layer of hydrogen compressed into a liquid by increasing pressures. That liquid conducts electricity, which powers Jupiter’s enormous magnetic field. Deeper still, the spacecraft will look for evidence of a core — a dense nugget of heavier elements that most scientists think exists, but has never been observed. Juno will make precise measurements of how Jupiter’s gravity tugs on the spacecraft, which should reveal whether a core is present.
Juno will also get an unprecedented glimpse of Jupiter’s poles. To avoid the most dangerous radiation belts that surround the gas giant — which over the lifetime of the mission could fry the spacecraft with the equivalent of more than 100 million dental X-rays— Juno will take a long elliptical dive around the planet on every orbit. The spacecraft will fly directly over Jupiter’s magnetically intense auroras, and could spot unusual circulation patterns that resemble a hexagon-shaped feature parked on Saturn’s north pole.
The lessons that scientists learn from Jupiter will apply to other gas giants, including those outside the Solar System. “If we understand how it formed, we’ll have a much better handle on giant-planet influences in planetary systems around other stars,” Fletcher says.
Juno will provide scientists’ last chance to look at Jupiter for a long time. It is scheduled to make 37 total orbits before performing a kamikaze run in early 2018, burning up inside the planet’s clouds to keep it from contaminating the moon Europa. The only other mission planned to the gas giant is the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) spacecraft, which could launch as early as 2022 and will focus mainly on the moon Ganymede.
- Journal name:
- Date published: | 0.878649 | 3.885557 |
Crescent ♋ Cancer
Moon phase on 6 June 2035 Wednesday is New Moon, less than 1 day young Moon is in Gemini.Share this page: twitter facebook linkedin
Moon rises at sunrise and sets at sunset. It's part facing the Earth is completely in shadow.
Moon is passing about ∠21° of ♊ Gemini tropical zodiac sector.
Lunar disc is not visible from Earth. Moon and Sun apparent angular diameters are ∠1973" and ∠1891".
Next Full Moon is the Strawberry Moon of June 2035 after 14 days on 20 June 2035 at 19:37.
There is high New Moon ocean tide on this date. Combined Sun and Moon gravitational tidal force working on Earth is strong, because of the Sun-Moon-Earth syzygy alignment.
At 03:21 on this date the Moon completes the old and enters a new synodic month with lunation 438 of Meeus index or 1391 from Brown series.
29 days, 6 hours and 39 minutes is the length of new lunation 438. This is the year's shortest synodic month of 2035. It is 33 minutes shorter than next lunation 439 length.
Length of current synodic month is 6 hours and 5 minutes shorter than the mean length of synodic month, but it is still 4 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠354.2°. At beginning of next synodic month true anomaly will be ∠9.1°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
Moon is reaching point of perigee on this date at 11:36, this is 13 days after last apogee on 24 May 2035 at 09:19 in ♐ Sagittarius. Lunar orbit is starting to get wider, while the Moon is moving outward the Earth for 14 days ahead, until it will get to the point of next apogee on 20 June 2035 at 12:30 in ♐ Sagittarius.
This perigee Moon is 357 357 km (222 051 mi) away from Earth. This is the year's closest perigee of 2035. It is 5 151 km closer than the mean perigee distance, but it is still 932 km farther than the closest perigee of 21st century.
7 days after its descending node on 30 May 2035 at 10:00 in ♓ Pisces, the Moon is following the southern part of its orbit for the next 5 days, until it will cross the ecliptic from South to North in ascending node on 11 June 2035 at 20:42 in ♍ Virgo.
21 days after beginning of current draconic month in ♍ Virgo, the Moon is moving from the second to the final part of it.
12 days after previous South standstill on 25 May 2035 at 00:53 in ♑ Capricorn, when Moon has reached southern declination of ∠-18.782°. Next day the lunar orbit moves northward to face North declination of ∠18.820° in the next northern standstill on 7 June 2035 at 10:40 in ♋ Cancer.
The Moon is in New Moon geocentric conjunction with the Sun on this date and this alignment forms Sun-Moon-Earth syzygy. | 0.837327 | 3.073928 |
The known irregular satellites of the giant planets are dormant comet-like objects that reside on stable prograde and retrograde orbits in a realm where planetary perturbations are only slightly larger than solar ones. Their size distributions and total numbers are surprisingly comparable to one another, with the observed populations at Jupiter, Saturn, and Uranus having remarkably shallow power-law slopes for objects larger than 8-10 km in diameter. Recent modeling work indicates that they may have been dynamically captured during a violent reshuffling event of the giant planets ~3.9 billion years ago that led to the clearing of an enormous, 35 M ⊕ disk of comet-like objects (i.e., the Nice model). Multiple close encounters between the giant planets at this time allowed some scattered comets near the encounters to be captured via three-body reactions. This implies the irregular satellites should be closely related to other dormant comet-like populations that presumably were produced at the same time from the same disk of objects (e.g., Trojan asteroids, Kuiper Belt, scattered disk). A critical problem with this idea, however, is that the size distribution of the Trojan asteroids and other related populations do not look at all like the irregular satellites. Here we use numerical codes to investigate whether collisional evolution between the irregular satellites over the last ~3.9 Gyr is sufficient to explain this difference. Starting with Trojan asteroid-like size distributions and testing a range of physical properties, we found that our model irregular satellite populations literally self-destruct over hundreds of Myr and lose ~99% of their starting mass. The survivors evolve to a low-mass size distribution similar to those observed, where they stay in steady state for billions of years. This explains why the different giant planet populations look like one another and provides more evidence that the Nice model may be viable. Our work also indicates that collisions produce ~0.001 lunar masses of dark dust at each giant planet, and that non-gravitational forces should drive most of it onto the outermost regular satellites. We argue that this scenario most easily explains the ubiquitous veneer of dark carbonaceous chondrite-like material seen on many prominent outer planet satellites (e.g., Callisto, Titan, Iapetus, Oberon, and Titania). Our model runs also provide strong indications that the irregular satellites were an important, perhaps even dominant, source of craters for many outer planet satellites. | 0.919765 | 3.958797 |
Most people know that some planets have moons but would be surprised to know that some asteroids do, too. According to Joshua Emery, assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville, about 20 percent of them do.
Emery is part of an international team of planetary astronomers, led by Franck Marchis of the Carl Sagan Center of the SETI Institute in Mountain View, Calif., searching for moons around asteroids. The discovery of moons around asteroids is important because it can provide clues to the asteroid's formation.
Emery and his team's research has focused on the triple asteroid Minerva, the fourth asteroid located in the main-belt--which houses most of the solar system's asteroids-- known to possess two moons.
"Minerva was thought to be a pretty typical, unremarkable asteroid until we discovered its two moons," said Emery. "Now, interest in this system has grown, and through a lot of new observations from both ground-based and space-based telescopes, we have developed a much more detailed understanding of Minerva and its moons."
The team studied the asteroid in detail using the large W.M. Keck telescope in Hawaii and a small robotic telescope at Kitt Peak in Arizona. By piecing together old and new observations, the astronomers were able to make precise determinations of the moons' orbits. With shape, size, and mass in hand, the scientists then derived the asteroid's density--determining that Minerva is different than the other large asteroids in the main-belt.
"All other large main-belt asteroids with one or more moons are very porous," said Emery. "Such high porosity strongly suggests that they are piles of rubble held together by gravity rather than solid rocks. Imagine an asteroid being completely blasted apart in a collision, then the pieces coalescing back together--this is how we think most of these large, multiple asteroid systems form. From these glimpses into the interior structure of asteroids, we gain insight not only into the history and formation of multiple asteroid systems, but also the structure and origin of asteroids in general."
The results of the group's findings were released at the EPSC-DPS meeting in Nantes, France. Other members of the international team of planetary astronomers are J.E. Enriquez, of Carl Sagan Center at the SETI Institute, Calif.; P. Descamps, J. Berthier, and F. Vachier of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France; J. Durech of Charles University, Prague, Czech republic; P. Dalba, UC Berkeley, Calif.; A.W. Harris of DLR, Berlin, Germany; J. Melbourne of Caltech, Pasadena, Calif.; A.N. Stockton and T.J. Dupuy of the University of Hawaii, Honolulu; and C.D. Fassnacht of the University of California at Davis, Calif. | 0.830042 | 3.902715 |
As NASA works through proposals for an asteroid retrieval mission, a new paper shows that there are other research groups considering which asteroids to pick first.
One scientific team has identified 12 “Easily Retrievable Objects” in our solar system that are circling the sun and would not cost too much to retrieve (in relative terms, of course!)
The definition of an ERO is an object that can be captured and brought back to a stable gravitational point near Earth (called a Lagrange point, or more specifically the L1/L2 points between the sun and the Earth.) The change in speed necessary in these objects to make them easily retrievable is “arbitrarily” set at 500 meters per second (1,641 feet/second) or less, the researchers stated.
Catching the objects wouldn’t just be a technology demonstration, but also could shed some light into how the solar system formed. Asteroids are generally considered leftovers of the early days of the neighborhood; under our current understanding of the solar system’s history, a spinning disc of gas and dust gradually clumped into rocks and other small objects, which eventually crashed into each other and formed planets.
Also, steering these objects around has another benefit: teaching humans how to deflect potentially hazardous asteroids from smacking into the Earth and causing damage. As we were reminded about earlier this year, even smaller rocks such as the one that broke up over a portion of Russia can be hazardous.
There are at least a couple of big limitations to the plan. The first is to make sure not to put the asteroid in a path that would hit the Earth. The second is that he L1 and L2 points are somewhat unstable, so over time the asteroid would drift from its spot. It would need a nudge every so often to keep it in that location.
That said, NASA is taking a serious look at the matter, as well as two groups that would like to mine asteroids: Planetary Resources and Deep Space Industries.
For the curious, this is the complete list of possible asteroids: 2006 RH120, 2010 VQ98, 2007 UN12, 2010 UE51, 2008 EA9, 2011 UD21, 2009 BD, 2008 UA 202, 2011 BL45, 2011 MD, 2000 SG344 and 1991 VG.
More details are available in the paper, “Easily retrievable objects among the NEO population“, which is published in the August 2013 edition of Celestial Mechanics and Dynamical Astronomy. A preprint version is also available on Arxiv. | 0.915402 | 3.592477 |
On the Moon, it is easy to remember where you parked. In December of 1972, Apollo 17
astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon
in the Taurus-Littrow
valley, while colleague Ronald Evans orbited overhead. This sharp image
was taken by Cernan as he and Schmitt roamed the valley floor
. The image
shows Schmitt on the left with the lunar rover
at the edge of Shorty Crater, near the spot
where geologist Schmitt discovered orange
lunar soil. The Apollo 17 crew returned with 110 kilograms of rock
and soil samples, more than was returned from any of the other lunar landing sites
. Now forty three years later, Cernan and Schmitt are still the last
to walk on the Moon
These clouds of interstellar dust and gas have blossomed 1,300 light-years away in the fertile star fields of the constellation Cepheus. Sometimes called the Iris Nebula, NGC 7023 is not the only nebula in the sky to evoke the imagery of flowers, though. Still, this deep telescopic view shows off the Iris Nebula's range of colors and symmetries in impressive detail. Within the Iris, dusty nebular material surrounds a hot, young star. The dominant color of the brighter reflection nebula is blue, characteristic of dust grains reflecting starlight. Central filaments of the dusty clouds glow with a faint reddish photoluminesence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Infrared observations indicate that this nebula may contain complex carbon molecules known as PAHs. The pretty blue petals of the Iris Nebula span about six light-years.
This intriguing monument can be found in Taiwan between the cities of Hualian and Taitong. Split into two sides, it straddles a special circle of latitude on planet Earth, near 23.5 degrees north, known as the Tropic of Cancer. Points along the Tropic of Cancer are the northernmost locations where the Sun can pass directly overhead, an event that occurs once a year during the northern hemisphere's summer solstice. The latitude that defines the Tropic of Cancer corresponds to the tilt of planet Earth's rotation axis with respect to its orbital plane. The name refers to the zodiacal constellation Cancer the Crab. Historically the Sun's position was within Cancer during the northern summer solstice, but because of the precession of Earth's axis, that solstice Sun is currently within the boundaries of Taurus. In this starry night scene the otherwise all white structure is colored by city lights, with its orange side just south of the Tropic of Cancer and the white side just north. Of course, there is a southern hemisphere counterpart of the Tropic of Cancer. It's called the Tropic of Capricorn.
No star dips below the horizon and the Sun never climbs above it in this remarkable image of 24 hour long star trails. Showing all the trails as complete circles, such an image could be achieved only from two places on planet Earth. This example was recorded during the course of May 1, 2012, the digital camera in a heated box on the roof of MAPO, the Martin A. Pomerantz Observatory at the South Pole. Directly overhead in the faint constellation Octans is the projection of Earth's rotational axis, the South Celestial Pole, at the center of all the star trail circles. Not so well placed as Polaris and the North Celestial Pole, the star leaving the small but still relatively bright circle around the South Celestial Pole is Beta Hydri. The inverted umbrella structure on the horizon at the right of the allsky field of view is the ground shield for the SPUD telescope. A shimmering apparition of the aurora australis also visited on this 24 hour night.
Why is the northern half of asteroid Vesta more heavily cratered than the south? No one is yet sure. This unexpected mystery has come to light only in the past few weeks since the robotic Dawn mission became the first spacecraft to orbit the second largest object in the asteroid belt between Mars and Jupiter. The northern half of Vesta, seen on the upper left of the above image, appears to show some of the densest cratering in the Solar System, while the southern half is unexpectedly smooth. Also unknown is the origin of grooves that circle the asteroid nears its equator, particularly visible on this Vesta rotation movie, and the nature of dark streaks that delineate some of Vesta's craters, for example the crater just above the the image center. As Dawn spirals in toward Vesta over the coming months, some answers may emerge, as well as higher resolution and color images. Studying 500-km diameter Vesta is yielding clues about its history and the early years of our Solar System.
What's causing those strange dark streaks in the rings of Saturn? Prometheus. Specifically, an orbital dance involving Saturn's moon Prometheus keeps creating unusual light and dark streamers in the F-Ring of Saturn. Now Prometheus orbits Saturn just inside the thin F-ring, but ventures into its inner edge about every 15 hours. Prometheus' gravity then pulls the closest ring particles toward the 80-km moon. The result is not only a stream of bright ring particles but also a dark ribbon where ring particles used to be. Since Prometheus orbits faster than the ring particles, the icy moon pulls out a new streamer every pass. Above, several streamers or kinks are visible at once. The above photograph was taken in June by the robotic Cassini Spacecraft orbiting Saturn. The oblong moon Prometheus is visible on the far left.
When stars form, pandemonium reigns. A textbook case is the star forming region NGC 6559. Visible above are red glowing emission nebulas of hydrogen, blue reflection nebulas of dust, dark absorption nebulas of dust, and the stars that formed from them. The first massive stars formed from the dense gas will emit energetic light and winds that erode, fragment, and sculpt their birthplace. And then they explode. The resulting morass can be as beautiful as it is complex. After tens of millions of years, the dust boils away, the gas gets swept away, and all that is left is a naked open cluster of stars.
Of course, everyone is concerned about what to wear to a solar eclipse. No need to worry though, nature often conspires to project images of the eclipse so that stylish and appropriate patterns adorn many visible surfaces - including clothing - at just the right time. Most commonly, small gaps between leaves on trees can act as pinhole cameras and generate multiple recognizable images of the eclipse. In Madrid to view the 2005 October 3rd annular eclipse of the Sun, astronomer Philippe Haake met a friend who had another inspiration. The result, a grid of small holes in a kitchen strainer produced this pattern of images on an 'eclipse shirt'. While Yesterday's solar eclipse was total only along a narrow path beginning in northern Canada, extending across the Arctic, and ending in China, a partial eclipse could be seen from much of Europe and Asia.
This bright, beautiful spiral galaxy is Messier 64, sometimes known as the Black Eye Galaxy. M64 lies about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. The dark clouds along the near-side of M64's central region that give the galaxy its black-eye appearance are enormous obscuring dust clouds associated with star formation, but they are not the galaxy's only peculiar feature. Observations show that M64 is actually composed of two concentric, counter-rotating systems of stars, one in the inner 3,000 light-years and another extending to about 40,000 light-years and rotating in the opposite direction. The dusty black eye and bizarre rotation is likely the result of a merger of two different galaxies.
Might it rain cold methane on Saturn's Titan? Recent analyses of measurements taken by the Huygen's probe that landed on Titan in 2005 January indicate that the atmosphere is actually saturated with methane at a height of about 8 kilometers. Combined with observations of a damp surface and lakes near the poles, some astrobiologists conclude that at least a methane drizzle is common on parts of Titan. Other astrobiologists reported computer models of the clouded moon that indicate that violent methane storms might even occur, complete with flash floods carving channels in the landscape. The later scenario is depicted in the above drawing of Titan. Lightning, as also depicted above, might well exist on Titan but has not been proven. The findings increase speculation that a wet Titanian surface might be hospitable to unusual forms of life.
Last week, crew members of the International Space Station (ISS) watched carefully as the Space Shuttle Discovery did a planned but unusual back flip upon approach. Discovery Commander Eileen Collins guided the shuttle through the flip, which was about 200 meters from the ISS when the above picture was taken. The ISS crew took detailed images of the dark heat shield tiles underneath during a 90-second photo shoot. The images are being analyzed to assess the condition of the dark heat shield. Later the shuttle docked with the space station. On the more usually photographed top side of the Space Shuttle, the above image shows Discovery's cargo bay doors open toward a distant Earth below.
Imagine a pipe as wide as a state and as long as half the Earth. Now imagine that this pipe is filled with hot gas moving 50,000 kilometers per hour. Further imagine that this pipe is not made of metal but a transparent magnetic field. You are envisioning just one of thousands of young spicules on the active Sun. Pictured above is perhaps the highest resolution image yet of these enigmatic solar flux tubes. Spicules dot the above frame of solar active region 10380 that crossed the Sun in June, but are particularly evident as a carpet of dark tubes on the right. Time-sequenced images have recently shown that spicules last about five minutes, starting out as tall tubes of rapidly rising gas but eventually fading as the gas peaks and falls back down to the Sun. These images also indicate, for the first time, that the ultimate cause of spicules is sound-like waves that flow over the Sun's surface but leak into the Sun's atmosphere.
On August 13, 2002, while counting Perseid meteors under dark, early morning Arizona skies, Rick Scott set out to photograph their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy, most too faint to be seen by the unaided eye. Flashing from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized the hurtling grain of cosmic sand, a piece of dust from Comet Swift-Tuttle. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda, about 2 million light-years away, is the most distant object easily visible to the naked-eye.
Comet 57P has fallen to pieces, at least 19 of them. Orbiting the Sun every 6 years or so this faint comet - also christened Comet 57P/du Toit-Neujmin-Delporte for its three 1941 co-discoverers - is simply 57th on the list of comets known to be periodic, beginning with Comet 1P/Halley. In mid July, responding to reports of a new object possibly associated with Comet 57P, astronomers were able to construct this mosaic of deep sky images identifying a surprising 19 fragments (circled) strung out behind the cometary coma and nucleus itself (far left). The full mosaic spans about a million kilometers at the distance of the comet, while the individual pieces detected are probably a few tens to a few hundred meters across. Stress produced as sunlight warmed the icy, rocky nucleus likely contributed to the fragmentation. In fact, when last seen passing through the inner solar system in 1996, Comet 57P brightened unexpectedly, indicating a sudden increase in surface activity.
This dramatic, garishly colored image was captured with a low-light level camera on 2001 June 7. It shows what appears to be a "burning tree" above the National Cheng Kung University campus in Tainan City, Taiwan ... but the burning tree is actually a fleeting red sprite 300 kilometers away. Red sprites are recently discovered and still poorly understood optical flashes seen dancing at altitudes of 30 to 90 kilometers above thunderstorms. Cousins to lightning bolts, red sprites occur near the edge of the atmosphere and have been glimpsed by astronauts from orbit. What ever their cause, the red sprite flashes usually last only tenths to hundredths of a second and characteristically take on shapes which researchers describe as columns, fingers, trees, or carrots.
The Crescent Nebula is a rapidly expanding shell of gas surrounding a dying star. In this recently released image by the Hubble Space Telescope, a bright dynamic part of the nebula three light-years across is shown in representative color. The Crescent Nebula began to form about 250,000 years ago as central Wolf-Rayet star WR 136 began to shed its outer envelope in a strong stellar wind, expelling the equivalent of our Sun's mass every 10,000 years. This wind has been impacting surrounding interstellar gas, compacting it into a series of complex shells, and lighting it up. The Crescent Nebula, also known as NGC 6888, lies about 4,700 light-years away in the constellation of Cygnus and can only be seen through a telescope. Star WR 136 will probably undergo a supernova explosion sometime in the next million years.
On May 21, viewed from the continental US, a star winked out as it passed behind the dark limb of the first-quarter Moon. The star, Regulus, is hotter than the sun, about 69 light-years distant, and shines in Earth's skies as the brightest star in the constellation Leo, the Lion. The Moon is the brightest object in the night sky and is less than 1.5 light-seconds away. As illustrated in this multiple-exposure photograph, such lunar occultations of bright stars can be majestic to watch. Their exact timing depends on the observer's location but they are not particularly rare occurrences. Astronomers can use lunar occultations to help map the surface of the Moon.
Sometimes you can't see the forest for the trees. But if you look closely at the center of the above photograph, you will see a whole spiral galaxy behind the field of stars. Named Dwingeloo 1, this nearby galaxy was only discovered recently (1994) because much of its light was obscured by dust, gas and bright stars of our own Milky Way Galaxy. In fact, all the individually discernible stars in the above photograph are in our Galaxy. Dwingeloo 1 turned out to be a large galaxy located only five times as distant as the closest major galaxy - M31.
Three thousand light years away, a dying star throws off shells of glowing gas. This image from the Hubble Space Telescope reveals "The Cat's Eye Nebula" to be one of the most complex planetary nebulae known. In fact, the features seen in this image are so complex that astronomers suspect the bright central object may actually be a binary star system. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images reveal them to be stars surrounded by cocoons of gas blown off in the late stages of stellar evolution.
Imagine a hurricane that lasted for 300 years! Jupiter's Great Red Spot indeed seems to be a giant hurricane-like storm system rotating with the Jovian clouds. Observed in 1655 by Italian-French astronomer Jean-Dominique Cassini it is seen here over 300 years later - still going strong - in a mosaic of recent Galileo spacecraft images. The Great Red Spot is a cold, high pressure area 2-3 times wider than planet Earth. Its outer edge rotates in a counter clockwise direction about once every six days. Jupiter's own rapid rotation period is a brief 10 hours. The Solar System's largest gas giant planet, it is presently well placed for evening viewing. (APOD thanks to Alan Radecki for assembling a preliminary mosaic from the Galileo imagery!)
Astronomers using NASA's Voyager spacecraft to search for a ring system around Jupiter discovered these faint rings in 1979. Unlike Saturn's bright rings which are composed of chunks of rock and ice, Jupiter's rings appear to consist of fine particles of dust. One possibility is that the dust is produced by impacts with Jupiter's inner moons. This false color image has been computer enhanced. | 0.938887 | 3.838879 |
Question 1 What is a Solar system? Name the different celestial objects which are members of the Solar system?
Question 2 What are planets?How many planets are there in a Solar system?
Question 3 Name all the planets of Solar system?
Question 4 What are inner and outer planets? Name them?
Question 5 How can you distinguish between planets and stars at night?
Question 6 What are the various environmental conditions on Earth which are responsible for the existence and continuation of life?
Question 7 What is the consequence of Rotation of Earth on axis?
Question 8 What is the consequence of motion of tilted Earth around the Sun?
Question 9 Why life is not possible on other planets except Earth?
Question 10 Define the term morning star and evening star?
Question 11 Why planet Mercury shows phases like the Moon?
The Solar System
Solar System consists of the Sun, the eight Planets and their Satellites (or moons), and millions of smaller celestial objects such as Asteroids, Comets and Meteoroids. The Sun is at the centre of the Solar System and all other objects are revolving around it in fixed elliptical paths called orbits.
The eight planets of the Solar System (in order of their increasing distances from the Sun) are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All these planets are orbiting around the Sun. All the planets (except Mercury and Venus) have natural satellites (or moons) around them.
The satellites (or moons) revolve around the planets. When the planets move around the Sun, then their satellites (for moons) also move along with them.
Asteroids are small rocky bodies which revolve around the Sun between the orbits of the planets Mars and Jupiter.Comets and meteoroids are also the minor members of the Solar System which revolve around the Sun.
The Sun is the biggest object in the Solar System. Because of its great size, the Sun has a gravitational force (or gravitational pull). The gravitational force of the Sun keeps the Solar system together and controls the movements of planets and other members of the Solar System.
The Sun is the the star around which the Earth and other planets revolve.The Sun is a medium-sized star and of average brightness. The Sun appears to be bigger and brighter because it is much more nearer to the Earth than any other star.
The Sun is a star having a system of planets around it with life on one of its planets called Earth.
The temperature at the surface of the Sun is about 6000°C. It is a sphere of hot gases. The Sun consists mostly of hydrogen gas. The nuclear fusion reactions taking place in the centre of the Sun (in which hydrogen is converted into helium), produce a tremendous amount of energy in the form of heat and light.
The Sun is the main source of heat and light energy for all the planets of the Solar System (including the Earth) and their satellites, etc. The planets and other objects in the sky reflect a part of the sunlight falling on them due to which they shine and become visible to us.
Planets are the large celestial objects (or celestial bodies) which revolve around the Sun in closed elliptical paths called orbits. There are 8 major planets (including the Earth).
The planets of the Solar System are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
The planets shine because they reflect the light of the Sun which falls on them. Since the planets are much nearer to us than the stars, they appear to be big and do not twinkle at night.
The stars appear to twinkle at night but the planets do not twinkle at all. The planets move around the Sun from west to east, so the relative positions of the planets in the night sky keep changing day by day.
The planets are very small as compared to the Sun or other stars. Every planet has its own fixed path (called orbit) in which it revolves (or moves) around the Sun. Since all the planets revolve in their separate, fixed paths (or fixed orbits), they do not collide with one another while revolving around the Sun.
Out of the 8 planets of the Solar System, 5 planets, Mercury, Venus, Mars, Jupiter and Saturn can be seen easily with the naked eye, so they were known to the ancient astronomers. The 2 planets, Uranus and Neptune are very far off and have been discovered with the help of a telescope.
The first four planets are called inner planets. The four inner planets (Mercury, Venus, Earth and Mars) are made of rocks and have metallic cores.The four inner planets are small and dense bodies having solid surfaces like our Earth. The inner planets have very few natural satellites (or moons)
The planets outside the orbit of Mars are called outer planets. Thus, Jupiter, Saturn, Uranus and Neptune are called outer planets. The outer planets are much farther off from the Sun than the inner planets. The four outer planets are giant planets (very, very big planets). The four outer planets are made mainly of hydrogen and helium gases, and not of rock and metal. They do not have solid surfaces at all. The outer planets have ring systems around them. The outer planets also have a large number of natural satellites (or moons) around them.
The time taken by a planet to complete one revolution around the Sun is called period of revolution. As the distance of a planet from Sun increases, its period of revolution also increases.
The time taken by a planet to complete one rotation on its axis, is called its period of rotation. The time taken by different planets to rotate once on their axis (or period of rotation), is also different.
1) Mercury is the planet which is nearest to the Sun.
2) It is very hot during the day.
3) Mercury is the smallest planet of the Solar System.
4) The planet Mercury has a rocky surface which is covered with craters.
5) Mercury is a planet which is quite difficult to see. Mercury planet is visible just before sun-rise or just after sun-set, near the horizon. So, planet Mercury can be seen only at those places where trees and other buildings do not obstruct the view of the horizon.
6) When planet Mercury is visible just before sun-rise in the morning, it is called a Morning Star and when it is visible just after sun-set in the evening, then it is called an Evening Star. The planet Mercury can be seen either as a Morning Star in the eastern sky just before sun-rise or as an Evening Star in the western sky just after sun-set.
7) Planet Mercury can be seen as a Morning Star or as an Evening Star because it lies inside the orbit of the Earth. Mercury is termed as Morning Star or Evening Star because it is a fairly bright object in the sky and appears like a star. In fact, Mercury shines because it reflects light from the Sun.
Planet Mercury shows phases like the Moon
Mercury lies inside the Earth’s orbit. So, as Mercury revolves around the Sun, its sun-lit surface is visible in varying amounts from the Earth. This produces phases of Mercury.
8) No life can exist on the planet Mercury because it is extremely hot and has no water on it. Mercury has also no atmosphere to prevent the deadly ultraviolet radiations of the Sun from reaching its surface.
9) Mercury has no satellite.
1) Venus is the second planet from the Sun.
2) Venus rotates on its axis from east to west (whereas Earth rotates on its axis from west to east). Due to this, on Venus the Sun would rise in the west and set in the east.
3) Venus is a rocky planet.
4) The planet Venus has a dense atmosphere which consists almost entirely of carbon dioxide gas.
5) Venus is the brightest planet in the night sky. The planet Venus appears very bright because its cloudy atmosphere reflects 75 per cent of the light which it receives from the Sun. Venus reflects more sunlight than any other planet of the Solar System and hence it appears to be the brightest planet.
6) Being quite near to the Sun, the planet Venus is very hot. The planet Venus also gets heated excessively by the trapping of Sun’s heat rays by carbon dioxide gas present in its atmosphere (which is called greenhouse effect).
7) The planet Venus is also called a Morning Star or an Evening Star. The planet Venus can be seen either as a Morning Star in the eastern sky just before sun-rise or as an Evening Star in the western sky just after sun-set.
8) The planet Venus also shows phases like the Moon. Venus lies inside the Earth’s orbit. So, as Venus revolves around the Sun, its sun-lit surface is presented to the Earth in varying amounts. This produces the phases of Venus.
9) Life cannot exist on the planet Venus because it is extremely hot, it has no water and there is no sufficient oxygen in its atmosphere,.
10) Venus has no satellite.
11) Venus planet is called Shukra Graha in Hindi.
1) The Earth is spherical in shape. When viewed from the outer space, the Earth appears to be a blue and green ball due to the reflection of sunlight from water and land on its surface.
2) Earth is the only planet in the Solar System on which life is known to exist.
3) The two major factors which are responsible for the existence of life on Earth are :
a) The distance of Earth from the Sun is such that it has the correct temperature range for the existence of water and survival of life.
b) Size of the Earth is such that it has sufficient gravitational field to hold on to an atmosphere of many gases (like oxygen and carbon dioxide) which are needed for the evolution and maintenance of life.
The various environmental conditions available on Earth which are responsible for the existence and continuation of life on Earth are as follows:
(1) The Earth has an atmosphere which has sufficient oxygen, the gas we need in order to live. The Earth’s atmosphere also supplies carbon dioxide needed for the preparation of food by photosynthesis by the plants.
(2) The Earth has large quantities of water: Earth is the only planet to have lots of water. This water helps in the evolution and maintenance of life on Earth.
(3)The Earth has a suitable temperature range for the existence of life. The Earth is nether too hot nor too cold.
(4) The Earth has a protective blanket of ozone layer high up in the atmosphere. This ozone layer absorbs most of the extremely harmful ultraviolet radiations coming from the Sun and prevents them from reaching the Earth and hence protects the living things on the Earth.
4) The Earth has two types of motion: (1) the Earth rotates on its axis, and (2) the Earth revolves around the Sun.
The Earth rotates (or spins) on an imaginary axis which passes through its North and South Poles.The Earth completes one rotation on its axis in 24 hours which we call one day. The Earth rotates (or spins) on its axis from west to east. The axis of rotation of Earth is slightly tilted with respect to the plane of its orbit (or path) around the Sun. The Earth rotates on its axis in the tilted position and it also revolves around the Sun in the same tilted position throughout.
Consequence of the rotation of Earth on its axis is that it causes day and night on the Earth. The Earth rotates (or spins) on its axis and also revolves (or moves) around the Sun in an elliptical orbit. The Earth takes 1 year to complete one revolution around the Sun.
An important consequence of the motion of tilted Earth causes different seasons on the Earth (such as summer, autumn, winter and spring).
5) The Earth has one natural satellite called Moon.
6) Earth planet is called ‘Prithvi Graha.
1) Mars is also called the red planet because its surface appears red.
2) Mars is visible from the Earth for most part of the year.Mars (and all other planets beyond Mars) do not appear as Morning Stars or Evening Stars, and they also do not show phases like the Moon. This is because they all lie outside the Earth’s orbit around Sun.
3) Mars is a small planet having a small mass. Since the planet Mars is very far off from the Sun, so it is quite a cold planet.
4) Mars is a rocky planet. Mars has a thin atmosphere as compared to the Earth. The thin atmosphere of Mars contains mainly carbon dioxide with small amounts of nitrogen, oxygen, noble gases and water vapour.
5) Mars has two natural satellites.
6) Mars planet is called ‘Mangal Graha’ in Hindi.
1) Jupiter is the fifth planet from the Sun.
2) Jupiter is the biggest planet of the Solar System. It is almost twice as large as rest of the planets put together.
3) The mass of Jupiter is also more than the combined mass of all other planets. The diameter of Jupiter is 11 times the diameter of the Earth and its mass is about 318 times that of the Earth.
4) Because of its very big size, Jupiter can be seen easily in the night sky.
5) Being very far off from the Sun, Jupiter receives much less heat and light from the Sun as compared to the Earth and Mars.
6)Jupiter appears to be a very bright object in the night sky. Jupiter’s bright appearance is due to the fact that it has a thick cloudy atmosphere which reflects most of the sunlight falling on it.
7) Jupiter rotates very rapidly on its axis.
8) Jupiter is made mainly of hydrogen and helium. Life cannot exist on the planet Jupiter because it has poisonous gases (like methane and ammonia) in its atmosphere.
8) Jupiter is a very cold planet.
9) Jupiter has 28 satellites (or moons). It has also some faint rings around it.
10) Jupiter planet is called ‘Brihaspati Graha’ in Hindi.
1) Saturn is the sixth planet from the Sun.
2) After Jupiter, Saturn is the second biggest planet of the Solar System.
3) Saturn is also made up mainly of hydrogen and helium.
4) It is the least dense among all the planets of the Solar System. The density of Saturn is even less than that of water.
5) Saturn has a system of colourful rings which surround it . Three distinct sets of rings around Saturn are visible from the Earth. Saturn is the only planet with a system of well-developed rings encircling it. The rings of Saturn are made up of tiny particles, all orbiting the Saturn like miniature satellites.
6) The presence of a well-developed system of rings around Saturn makes it unique in the Solar System.
7) Being far off from the Sun, Saturn is an extremely cold planet. So, no life can exist on Saturn.
8) Saturn has the maximum number of satellites (or moons) of all the planets in the Solar System. Saturn has 30 satellites (or moons).
9) Planet Saturn is called ‘Shani Graha’ in Hindi.
1) Uranus is the seventh planet from the Sun .
2) It can be seen only with the help of a large telescope.
3) Uranus is almost four times that of the Earth, it appears as a small disc through a telescope. This is because Uranus is very, very far off from the Earth.
4) Uranus also rotates on its axis from east to west.It has highly tiled axis of rotation. As a result of the highly tilted axis of rotation, Uranus appears to roll on its side while orbiting around the Sun.
5) Uranus is made up mainly of hydrogen and helium. Uranus is an extremely cold planet.
6) It is also surrounded by an atmosphere of poisonous gases. Due to these reasons, no life can exist on the planet Uranus.
7) The planet Uranus has 21 satellites (or moons). It has also some rings around it.
8) Uranus planet is called Indra Graha’ in Hindi.
1) Neptune is the eighth planet from the Sun.
2) It is the most distant planet from the Sun.
3) Neptune is the second planet which was discovered with the help of a telescope.
4) The planet Neptune can be seen as a tiny blue-green speck even by using the most powerful telescope on the Earth.
5) Neptune is made up mainly of liquid and frozen hydrogen and helium gases. Neptune is an extremely cold planet. So, no life can exist on the planet Neptune.
6) Neptune has 8 satellites (or moons). It has also some rings around it.
7) Neptune planet is called ‘Varun Graha’ in Hindi. | 0.860494 | 3.158299 |
‘Einstein, gravitation and the scientists of the Empire c. 1919: highlights reel’, Honest History, 16 February 2016
The recent announcement of the discovery of gravitational waves (described as the scientific discovery of the century) set Honest History in search of relevant references from a century ago – the era when Einstein made his original breakthroughs. There are a number of references under ‘Albert Einstein’ in the Australian papers (via Trove) from 1916 to 1920. There are also some nice nuggets in The Times (via the Times Digital Archive, sign up through the National Library of Australia), among them a long article from Einstein himself and a testy response from a leading light of the British science community, who still seemed to be holding a candle for Sir Isaac Newton. There is also a particular Australian connection.
Einstein, Berlin 1920 (Wikimedia Commons)
On 28 November 1919, The Times printed an article by Einstein, headed ‘Einstein on his theory: time, space and gravitation: the Newtonian system’. It was translated, presumably from German, and ran to nearly 2000 words.
Einstein started with a reference to ‘the lamentable breach in the former international relations existing among men of science’ and ended by poking fun at the British confusion over whether he was ‘a Swiss Jew or a German man of science. In between, he gave a layperson’s explanation of theories in physics, including his own theory of relativity, both special and general. He then pointed out how relativity was incompatible with Galileo’s and Newton’s laws of motion, indicating ‘how a generalized theory of relativity must include the laws of gravitation’.
Einstein went on to consider some of the contradictions, referring to the new concept of ‘a warp in space’, how old concepts like ‘straight’ and ‘plane’ had lost their meaning, and that ‘the doctrine of space and time (kinematics) is no longer one of the absolute foundations of general physics’. He said the new theory of gravitation diverged greatly from Newton ‘with respect to its basal principle’ but it was difficult to detect differences in practical application.
One of the three cases of difference detected so far was ‘The deviation of light-rays in a gravitational field (confirmed by the [May 1919] English Solar Eclipse expedition)’. Einstein concluded on the ‘logical consistency’ of his theory but still recognised the foundational contribution of Newton to modern physics.
British science responds
Slightly sniffily, The Times leader writer, on the same page as Einstein’s article, while confessing not to follow the details and implications ‘with complete certainty’, recognised that the world of science had changed fundamentally, even if (this said with some relief) ‘the new conception will make little difference to the practical world’. The leader writer distanced him or herself from the contentions of a home-grown scientist, Professor Thomas Case, that basic conceptions in physics were little altered. The writer also noted that Einstein had not deigned to settle the question of whether he was a Swiss Jew or a German man of science.
Case had written (at length) to The Times the previous Saturday, 22 November, from his home in Weymouth. Case later became well-known as an opponent of Einstein and the controversy was getting under way in 1919. One can imagine Dons in Cambridge and Oxford reading Case’s letter closely as the short late autumn daylight retreated and the last leaves swirled in the breeze outside.
Case looked at what had come out of the English Solar Eclipse exhibition, considered some theoretical possibilities and opined that the challenge had been put out to ‘the learned world to decide whether Newton or Einstein is to be taken as the authority on space, time, motion, and the spatial universe’. He considered both men’s arguments and concluded firmly in favour of his fellow Britisher, Newton, although Einstein had sorted out some points of detail: ‘Professor Albert Einstein’s theory of space is deficient’.
Sir Isaac Newton (Wikipedia)
Meanwhile in Melbourne
Distinguished Australian historian, Humphrey McQueen, has during his career ranged widely over many strands of the discipline. (Search the Honest History site under ‘McQueen’ for some evidence of this.) In an article in The Age (Melbourne) in 2005, McQueen first described Albert Einstein’s early adventures demolishing the arcane concept of ‘aether’ before going on to look more broadly at the impact of Einstein on Australia. (The article included an extensive bibliography on aether and the reaction to Einstein in Australia.)
McQueen recorded that the 1919 eclipse, so assiduously studied on the other side of the world by Einstein and others, had also been followed closely in Australia, notably in The Argus newspaper in Melbourne. While The Argus‘s writers struggled to explain the concepts, interest persisted because Australia was the best site to view the next eclipse, scheduled for September 1922. Observations at this eclipse seemed to confirm that Einstein was on the right track, though a lecturer at the University of Melbourne, one CE Weatherburn, was not convinced, apparently playing a similar role in the Antipodes to that which Case had filled on the other side of the world.
Other Australian scientists and technical experts continued to pin their hopes on aether, long after Einstein had discredited it. CE Weatherburn had a street named after him in Canberra. It is just a few yards from Honest History’s bustling head office. Weatherburn’s shade may permit us to wonder, as we stroll along his street, whether his and Case’s attitudes to Einstein’s work were driven as much by Empire loyalties (and perhaps by attitudes to Jews) as by scientific evidence. | 0.805017 | 3.099778 |
Crescent ♋ Cancer
Moon phase on 25 April 2069 Thursday is Waxing Crescent, 5 days young Moon is in Cancer.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 4 days on 21 April 2069 at 09:58.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing first ∠2° of ♋ Cancer tropical zodiac sector.
Lunar disc appears visually 0.2% wider than solar disc. Moon and Sun apparent angular diameters are ∠1910" and ∠1907".
Next Full Moon is the Flower Moon of May 2069 after 10 days on 6 May 2069 at 09:11.
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 5 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 857 of Meeus index or 1810 from Brown series.
Length of current 857 lunation is 29 days, 8 hours and 7 minutes. This is the year's shortest synodic month of 2069. It is 1 minute shorter than next lunation 858 length.
Length of current synodic month is 4 hours and 37 minutes shorter than the mean length of synodic month, but it is still 1 hour and 32 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠4.9°. At beginning of next synodic month true anomaly will be ∠21°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
4 days after point of perigee on 21 April 2069 at 02:57 in ♈ Aries. 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 4 May 2069 at 05:38 in ♎ Libra.
Moon is 375 246 km (233 167 mi) away from Earth on this date. Moon moves farther next 8 days until apogee, when Earth-Moon distance will reach 406 134 km (252 360 mi).
3 days after its descending node on 22 April 2069 at 04:46 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 6 May 2069 at 03:49 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.
1 day after previous North standstill on 24 April 2069 at 15:22 in ♊ Gemini, when Moon has reached northern declination of ∠19.914°. Next 13 days the lunar orbit moves southward to face South declination of ∠-19.911° in the next southern standstill on 9 May 2069 at 03:40 in ♐ Sagittarius.
After 10 days on 6 May 2069 at 09:11 in ♏ Scorpio, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.07614 |
Two groups have recently used the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC 2) to acquire new high-resolution images of the planet Neptune. Members of the WFPC-2 Science Team, lead by John Trauger, acquired the first series of images on 27 through 29 June 1994. These were the highest resolution images of Neptune taken since the Voyager-2 flyby in August of 1989. A more comprehensive program is currently being conducted by Heidi Hammel and Wes Lockwood. These two sets of observations are providing a wealth of new information about the structure, composition, and meteorology of this distant planet's atmosphere.
Neptune is currently the most distant planet from the sun, with an orbital radius of 4.5 billion kilometers (2.8 billion miles, or 30 Astronomical Units). Even though its diameter is about four times that of the Earth (49,420 vs. 12,742 km), ground-based telescopes reveal a tiny blue disk that subtends less than 1/1200 of a degree (2.3 arc-seconds). Neptune has therefore been a particularly challenging object to study from the ground because its disk is badly blurred by the Earth's atmosphere. In spite of this, ground-based astronomers had learned a great deal about this planet since its position was first predicted by John C. Adams and Urbain Leverrier in 1845. For example, they had determined that Neptune was composed primarily of hydrogen and helium gas, and that its blue color caused by the presence of trace amounts of the gas methane, which absorbs red light. They had also detected bright cloud features whose brightness changed with time, and tracked these clouds to infer a rotation period between 17 and 22 hours.
When the Voyager-2 spacecraft flew past the Neptune in 1989, its instruments revealed a surprising array of meteorological phenomena, including strong winds, bright, high-altitude clouds, and two large dark spots attributed to long-lived giant storm systems. These bright clouds and dark spots were tracked as they moved across the planet's disk, revealing wind speeds as large as 325 meters per second (730 miles per hour). The largest of the giant, dark storm systems, called the "Great Dark Spot", received special attention because it resembled Jupiter's Great Red Spot, a storm that has persisted for more than three centuries. The lifetime of Neptune's Great Dark Spot could not be determined from the Voyager data alone, however, because the encounter was too brief. Its evolution was impossible to monitor with ground-based telescopes, because it could not be resolved on Neptune's tiny disk, and its contribution to the disk-integrated brightness of Neptune confused by the presence of a rapidly-varying bright cloud feature, called the "Bright Companion" that usually accompanied the Great Dark spot.
The repaired Hubble Space Telescope provides new opportunities to monitor these and other phenomena in the atmosphere of the most distant planet. Images taken with WFPC-2's Planetary Camera (PC) can resolve Neptune's disk as well as most ground-based telescopes can resolve the disk of Jupiter. The spatial resolution of the HST WFPC-2 images is not as high as that obtained by the Voyager-2 Narrow-Angle Camera during that spacecraft's closest approach to Neptune, but they have a number of other assets that enhance their scientific value, including improved ultra-violet and infrared sensitivity, better signal-to-noise, and, and greater photometric accuracy.
The images of Neptune acquired by the WFPC-2 Science team in late June clearly demonstrate these capabilities. The side of the planet facing the Earth at the start of the program (11:36 Universal Time on July 27) was imaged in color filters spanning the ultraviolet (255 and 300-nm), visible (467, 588, 620, and 673- nm), and near-infrared (890-nm) parts of the spectrum. The planet then rotated 180 degrees in longitude, and the opposite hemisphere was imaged in a subset of these colors (300, 467, 588, 620, and 673-nm). The HST/WFPC-2 program more recently conducted by Hammel and Lockwood provides better longitude coverage, and a wider range of observing times, but uses a more restricted set of colors.
The ultraviolet pictures show an almost featureless disk that is slightly darker near the edge. The observed contrast increases in the blue, green, red, and near-infrared images, which reveal many of the features seen by Voyager 2, including the dark band near 60 S latitude and several distinct bright cloud features. The bright cloud features are most obvious in the red and infrared parts of the spectrum where methane gas absorbs most strongly (619 and 890 nm). These bright clouds thought to be high above the main cloud deck, and above much of the absorbing methane gas. The edge of the planet's disk also appears somewhat bright in these colors, indicating the presence of a ubiquitous, high-altitude haze layer.
The northern hemisphere is occupied by a single prominent cloud band centered near 30 N latitude. This planet-encircling feature may be the same bright cloud discovered last fall by ground-based observers. Northern hemisphere clouds were much less obvious at the time of the Voyager-2 encounter. The tropics are about 20 % darker than the disk average in the 890-nm images, and one of these images reveals a discrete bright cloud on the equator, near the edge of the disk. The southern hemisphere includes two broken bright bands. The largest and brightest is centered at 30 S latitude, and extends for least 40 degrees of longitude, like the Bright Companion to the Great Dark Spot. There is also a thin cloud band at 45 S latitude, which almost encircles the planet.
One feature that is conspicuous by its absence is the storm system known as the Great Dark Spot. The second smaller dark spot, DS2, that was seen during the Voyager-2 encounter was also missing. The absence of these dark spots was one of the biggest surprises of this program. The WFPC-2 Science team initially assumed that the two storm systems might be near the edge of the planet's disk, where they would not be particularly obvious. An analysis of their longitude coverage revealed that less than 20 degrees of longitude had been missed in the colors where these spots had their greatest contrast (467 and 588 nm). The Great Dark Spot covered almost 40 degrees of longitude at the time of the Voyager-2 fly-by. Even if it were on the edge of the disk, it would appear as a "bite" out of the limb. Because no such feature was detected, we concluded that these features had vanished. This conclusion was reinforced by the more recent observations by Hammel and Lockwood, which also show no evidence of discrete dark spots.
These dramatic changes in the large-scale storm systems and planet-encircling clouds bands on Neptune are not yet completely understood, but they emphasize the dynamic nature of this planet's atmosphere, and the need for further monitoring. Additional HST WFPC-2 observations are planned for next summer. These two teams are continuing their analysis of these data sets to place improved constraints on these and other phenomena in Neptune's atmosphere.
These almost true-color pictures of Neptune were constructed from HST/WFPC2 images taken in blue (467-nm), green (588- nm), and red (673-nm) spectral filters. There is a bright cloud feature at the south pole, near the bottom right of the image. Bright cloud bands can be seen at 30S and 60S latitude. The northern hemisphere also includes a bright cloud band centered near 30N latitude. The second picture was compiled from images taken after the planet had rotated about 180 degrees of longitude (about 9 hours later) to show the opposite hemisphere.
The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.
This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/. | 0.87123 | 3.959596 |
One of the most distinguishable human features is our upright mode of locomotion, which is unique among mammals. Scientists have proposed many ideas that might explain the circumstances that enabled our species to evolve as bipeds. Perhaps the most ‘out there’ theory proposed thus far comes from astronomers at the University of Kansas who claim that human bipedalism might have been triggered by giant cosmic explosions. But before you laugh, read on because, wild as it may sound, this theory has some interesting evidence backing it up.
Some time ago, scientists reported that ancient seabeds contain a layer of iron-60 isotopes. These rare isotopes cannot be made on Earth, which means their origin must be extraterrestrial, most likely the result of a supernova — a transient astronomical event that occurs during the last stellar evolutionary stages of massive star’s life. Because iron-60 has a known half-life, it is relatively easy to accurately date when the supernovae’s cosmic rays reached our planet.
Scientists traced the isotopic signatures to two major events: one 6.5 to 8.7 million years ago (300 light-years away from Earth) and the second 1.7 to 3.2 million years ago (163 light-years). That’s around the time of Homo habilis, the upright human ancestor nicknamed “handyman” because of their ability to master stone tool technology.
Based on this information, Adrian Melott and colleagues at the University of Kansas hypothesized what kind of changes these cosmic rays might have caused on Earth. One of the first things that should have happened was a dramatic increase in the rate of ionization of the lower atmosphere.
Ionization is the process by which an atom or molecule acquires a negative or positive charge by gaining or losing electrons. In this case, the cosmic rays knocked off electrons from molecules in the atmosphere. According to Melott, the supernova events would have increased ionization in the atmosphere by 50-fold. With so many free electrons in the atmosphere, cloud-to-ground lightning would have been much easier to occur, increasing the odds of forest fires.
“The bottom mile or so of atmosphere gets affected in ways it normally never does,” Melott said. “When high-energy cosmic rays hit atoms and molecules in the atmosphere, they knock electrons out of them — so these electrons are running around loose instead of bound to atoms. Ordinarily, in the lightning process, there’s a buildup of voltage between clouds or the clouds and the ground — but current can’t flow because not enough electrons are around to carry it. So, it has to build up high voltage before electrons start moving. Once they’re moving, electrons knock more electrons out of more atoms, and it builds to a lightning bolt. But with this ionization, that process can get started a lot more easily, so there would be a lot more lightning bolts.”
In time, savannas replaced torched forests in northeast Africa. Now, walking was far more advantageous for our ancestors than climbing trees. The upsurge in global wildfires is supported by the discovery of carbon deposits found in soils that correspond with the timing of the cosmic-ray bombardment.
“It is thought there was already some tendency for hominins to walk on two legs, even before this event,” said Melott, professorof physics & astronomy at the University of Kansas. “But they were mainly adapted for climbing around in trees. After this conversion to savanna, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright. They could see over the tops of grass and watch for predators. It’s thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors.”
That’s quite a great deal of speculation but the evidence suggests that such a scenario might have been possible — however improbable as it may sound. What about something like happening in the future? Slim chance, say the researchers who point to the fact that the nearest supernova candidate is now 652 light-years away from Earth. Instead, Melott says we should be cautious about a more immediate threat — solar flares.
“Betelgeuse is too far away to have effects anywhere near this strong,” Melott said. “So, don’t worry about this. Worry about solar proton events. That’s the danger for us with our technology — a solar flare that knocks out electrical power. Just imagine months without electricity.”
The findings appeared in the Journal of Geology. | 0.867071 | 3.83939 |
NASA's Sun Mission: NASA counts down to launch of first spacecraft to 'touch Sun'
NASA counted down Friday to the launch of a $1.5 billion spacecraft that aims to plunge into the Sun's sizzling atmosphere and become humanity's first mission to explore a star.
NASA counted down Friday to the launch of a $1.5 billion spacecraft that aims to plunge into the Sun's sizzling atmosphere and become humanity's first mission to explore a star. The car-sized Parker Solar Probe is scheduled to blast off on a Delta IV Heavy rocket from Cape Canaveral, Florida early Saturday.
The 65-minute launch window opens at 3:33 am (0733 GMT), and the weather forecast is 70 percent favorable for takeoff, NASA said.
The probe's main goal is to unveil the secrets of the corona, the unusual atmosphere around Sun. Not only is the corona about 300 times hotter than the Sun's surface, it also hurls powerful plasma and energetic particles that can unleash geomagnetic space storms and disrupt Earth's power grid.
"The Parker Solar Probe will help us do a much better job of predicting when a disturbance in the solar wind could hit Earth," said Justin Kasper, one of the project scientists and a professor at the University of Michigan.
'Full of mysteries'
The probe is protected by an ultra-powerful heat shield that is just 4.5 inches thick (11.43 centimeters). The shield should enable the spacecraft to survive its close shave with the center of our solar system, coming within 3.83 million miles (6.16 million kilometers) of the Sun's surface.
The heat shield is built to withstand radiation equivalent up to about 500 times the Sun's radiation here on Earth. Even in a region where temperatures can reach more than a million degrees Fahrenheit, the sunlight is expected to heat the shield to just around 2,500 degrees Fahrenheit (1,371 degrees Celsius).
Scorching, yes? But if all works as planned, the inside of the spacecraft should stay a cooler 85 F (29 C). The goal for the Parker Solar Probe is to make 24 passes through the corona during its seven-year mission.
"The sun is full of mysteries," said Nicky Fox, project scientist at the Johns Hopkins University Applied Physics Lab.
"We are ready. We have the perfect payload. We know the questions we want to answer."
The tools on board will measure the expanding corona and continually flowing atmosphere known as the solar wind, which solar physicist Eugene Parker first described back in 1958. Parker, now 91, recalled that at first, some people did not believe in his theory.
But then, the launch of NASA's Mariner 2 spacecraft in 1962 -- becoming the first robotic spacecraft to make a successful planetary encounter -- proved them wrong.
"It was just a matter of sitting out the deniers for four years until the Venus Mariner 2 spacecraft showed that, by golly, there was a solar wind," Parker said earlier this week.
He added that he is "impressed" by the Parker Solar Probe, calling it "a very complex machine."
Scientists have wanted to build a spacecraft like this for more than 60 years, but only in recent years did the heat shield technology advance enough to be capable of protecting sensitive instruments, according to Fox. Tools on board will measure high energy particles associated with flares and coronal mass ejections, as well as the changing magnetic field around the Sun.
"We will also be listening for plasma waves that we know flow around when particles move," Fox added.
"And last but not least, we have a white light imager that is taking images of the atmosphere right in front of the Sun."
When it nears the Sun, the probe will travel rapidly enough to go from New York to Tokyo in one minute -- some 430,000 miles (700,000 kilometers) per hour, making it the fastest human-made object. | 0.840951 | 3.107409 |
Since the mass of the moon is negligible, the gas shell around it must be very rarefied, i.e. practically absent. The main components of the gas shell were hydrogen, helium, neon, and argon. The highest density is observed at night and corresponds to about 2 · 105 cm – 3. in the daytime, the gas concentration drops to 104 cm – 3 in terms of density at the surface. Therefore, we can speak with good reason about the presence of some kind of gas shell around the moon.
The moon has practically no global magnetic field of a dipole nature. This circumstance explains the peculiarities of the interaction of the Moon with the stream of charged particles of the solar wind, which consists mainly of protons and electrons with the addition of ionized helium and other heavier elements with different degrees of ionization. The moon is a non-magnetic, relatively non-conductive and cold dielectric sphere. Continue reading
Like all bodies in nature, stars do not remain unchanged, they are born, evolve, and finally “die.” To trace the life path of stars and understand how they age, you need to know how they arise. In the past, this seemed like a big mystery; modern astronomers can already with great confidence describe in detail the paths leading to the appearance of bright stars in our night sky.
Not so long ago, astronomers believed that it takes millions of years to form a star from interstellar gas and dust. But in recent years, striking photographs have been taken of the area of the sky that is part of the Great Orion Nebula, where a small cluster of stars has appeared over the course of several years. In the pictures of 1947. in this place a group of three star-like objects was visible. By 1954 some of them became oblong, and by Continue reading
Scientists strongly believe that black holes really exist. Albert Einstein’s general theory of relativity predicted the existence of such objects back in 1917, and over the past decades, astronomers have found plenty of evidence of their presence in many areas of outer space.
More than 5 objects are known, which probably include black holes. However, there is only indirect evidence, but there is no conclusive evidence. The most likely candidate for black holes is the X-ray source Cygnus X-1, discovered in the early 1970s in X-binary systems. The mass of the source in this system, which can be estimated from the observed speed of the optical star in its orbit and Kepler’s laws, exceeds the limiting mass for a neutron star. The Chandra X-ray Observatory found in several galaxies with a high rate Continue reading | 0.919346 | 3.946358 |
We know that sun-grazing comets commonly sweep near our sun. Now astronomers have caught a comet on video at the moment it plunges into the sun and apparently disintegrates in the sun’s 100,000 degree (Kelvin) heat.
Astronomers made the announcement at the May 2010 meeting of the American Astronomical Society, happening now in Miami, Florida. You can see a large-format video here (might take a minute or two to load). Or look below for a small version of the video.
(NASA. UC Berkeley)
This video was captured by four post-doctoral fellows – solar physicists at UC Berkeley’s Space Sciences Laboratory – using instruments aboard NASA’s twin STEREO spacecraft, They tracked the comet as it approached the sun and estimated an approximate time and place of impact.
STEREO (Solar TErrestrial RElations Observatory), launched in 2006, consists of identical spacecraft orbiting the sun, one ahead of Earth and one behind the Earth, providing a stereo view of the sun.
The image at the top of this article, meanwhile, is a hydrogen-alpha observation of the sun’s edge from the Coronado instrument of the Mauna Loa Solar Observatory showing what the authors believe to be the comet approaching the solar limb.
The sun’s brightness generally prevents these so-called sun-grazing comets – which are icy, dusty rocky balls traveling in our solar system – from being seen close to the sun. This comet apparently survived the heat of the sun’s corona and disappeared in its chromosphere.
Claire Raftery, Juan Carlos Martinez-Oliveros, Samuel Krucker and Pascal Saint-Hilaire tracked the comet, concluding it was probably one of the Kreutz family of comets, a swarm of Trojan or Greek comets ejected from their orbit in 2004 by Jupiter, and making its first and only loop near the sun.
The team presented its data and images on Monday, May 24, at the Miami, Fla., meeting of the American Astronomical Society. Read the full press release.
And imagine the forces involved – the flight through space of this comet, from Jupiter’s vicinity to the inner solar system – the heat and blast from our parent star as the comet disintegrates on its final plunge toward the sun!
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says. | 0.893948 | 3.352001 |
One of the most mysterious and interesting known locations in our neighborhood of space is the center of our home galaxy, the Milky Way. It’s thought to contain a supermassive black hole, with a mass of some 4 million suns. Astronomers call this region and its possible black hole Sagittarius A* (aka Sgr A*, pronounced Sagittarius A-star). In 2016, Farhad Yusef-Zadeh of Northwestern University reported his discovery of an unusual filament in this region. The filament is about 2.3 light-years long and appears to curve around the site of the black hole. Now, another team of astronomers has employed a new technique to obtain a high-quality image of the curved filament. These astronomers said their new image supports the idea that the filament is pointing toward the black hole. The new image has led to some fascinating speculations as to the nature of this mystery filament.
With our improved image, we can now follow this filament much closer to the galaxy’s central black hole, and it is now close enough to indicate to us that it must originate there. However, we still have more work to do to find out what the true nature of this filament is.
Researchers have considered three possible explanations for the filament:
The first is that it is caused by high-speed particles kicked away from the supermassive black hole. A spinning black hole coupled with gas spiraling inwards can produce a rotating, vertical tower of magnetic field that approaches or even threads the event horizon, the point of no return for infalling matter. Within this tower, particles would be sped up and produce radio emission as they spiral around magnetic field lines and stream away from the black hole.
The second, more fantastic, possibility is that the filament is a cosmic string, theoretical, as-yet undetected objects that are long, extremely thin objects that carry mass and electric currents. Previously, theorists had predicted that cosmic strings, if they exist, would migrate to the centers of galaxies. If the string moves close enough to the central black hole it might be captured once a portion of the string crosses the event horizon.
The final option is that the position and the direction of the filament aligning with the black hole are merely coincidental superpositions, and there is no real association between the two. This would imply it is like dozens of other known filaments found farther away from the center of the galaxy. However, such a coincidence is quite unlikely to happen by chance.
Each of the scenarios being investigated would provide intriguing insight if proven true. The scientists’ statement continued:
For example, if the filament is caused by particles being ejected by Sgr A*, this would reveal important information about the magnetic field in this special environment, showing that it is smooth and orderly rather than chaotic.
The second option, the cosmic string, would provide the first evidence for a highly speculative idea with profound implications for understanding gravity, space-time and the Universe itself.
Evidence for the idea that particles are being magnetically kicked away from the black hole would come from observing that particles further away from Sgr A* are less energetic than those close in. A test for the cosmic string idea will capitalize on the prediction by theorists that the string should move at a high fraction of the speed of light. Follow-up observations with the VLA should be able to detect the corresponding shift in position of the filament.
Even if the filament is not physically tied to Sgr A*, the bend in the shape of this filament is still unusual. The bend coincides with, and could be caused by, a shock wave, akin to a sonic boom, where the blast wave from an exploded star is colliding with the powerful winds blowing away from massive stars surrounding the central black hole.
Co-author Miller Goss, from the National Radio Astronomy Observatory in Socorro, New Mexico, said:
We will keep hunting until we have a solid explanation for this object. And we are aiming to next produce even better, more revealing images.
Bottom line: Astronomers have obtained a new image of the 2.3-light-year-long filament that curves around Sagittarius A*, the region of our galaxy thought to contain a supermassive black hole.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says. | 0.880414 | 3.987108 |
It’s been a little more than 17 months since NASA’s Juno spacecraft arrived at Jupiter. What has the spacecraft been up to? Oh, not much…just unlocking the mysteries of the gas giant’s gravity, magnetic field, turbulent atmosphere, and brilliant auroras.
But that’s not all. The spacecraft also houses JunoCam, its color camera. JunoCam is unique because the public, rather than the mission scientists, determine what spots on Jupiter the camera will image. Before each flyby of the spacecraft, members of the open online JunoCam community propose, discuss, and vote on points of interest that JunoCam should examine up close.
Here’s the fun part: After each flyby is completed, the raw JunoCam images are posted online for anyone to download and process into polished pictures. Yes, some public-created images highlight the mission’s scientific goals.
But others take scientific gravitas and throw it out the window, looking to hit a more whimsical note. This is, after all, the digital age. Below are just some of these images, created by amateur astronomers, citizen scientists, and artists who looked at Jupiter and saw something a little bit different.
Jupiter as a Work of Impressionist Art
Although many astronomers have long considered the swirling storms on Jupiter to be beautiful works of art, this avant-garde interpretation of Jupiter’s Great Red Spot pays tribute to French impressionist painter Claude Monet and his famous Water Lilies series.
Jupiter’s south pole is no slouch when it comes to atmospheric turbulence, spots, and storms. This enhanced-color image from JunoCam’s early science results, taken from 52,000 kilometers above the atmosphere, combines snapshots taken over three separate orbits of the spacecraft. The patterns created by Jupiter’s complex magnetic field invoke the skies of Vincent van Gogh’s Wheatfield with Crows or Imperial Fritillaries in a Copper Vase. Some of the oval cyclone features are 1,000 kilometers wide.
And, of course, no astronomy-themed art gallery would be complete without a tribute to van Gogh’s The Starry Night. In this interpretation, a false-color image of Jupiter’s south pole is the backdrop for the iconic sleepy French village. Turbulent storms and atmospheric swirls are convincing substitutes for van Gogh’s postimpressionist-style sky.
A Mathematical Take on Jupiter
Some people just can’t stop themselves from spicing up their planetary science with a little galactic astronomy. This false-color view looking directly down at Jupiter’s south pole interprets the coils surrounding the bright pole as the spiral galaxy NGC 6814. The smaller spiral storms might even be background galaxies or bright foreground stars.
Is this the Great Red Spot or a psychedelic throwback to the 1960s? Trick question: It’s both! Artist Mik Petter created this mesmerizing take on Jupiter’s most prominent hurricane by converting JunoCam data into a colorful set of fractal-based swirls, highlighting the turbulence surrounding the centuries-old storm.
Fantasy, Sci-Fi, and Memes, Oh My!
Forget the man on the Moon. The face of Jupiter, also known as “Jovey McJupiterface,” is looking back at you. Here’s the whole image, which was snipped earlier: By flipping a JunoCam image upside down, one citizen scientist turned two of Jupiter’s pearly white storms into eyes suspended above a red, oval-shaped mouth.
Have you ever imagined what it would be like to live on a hunk of space rock where you could see planet rise every morning? Wonder no longer! With a little creative image manipulation, plus a foreground rockscape from Red Rock Canyon in Las Vegas, Nev., and a starry background, this JunoCam image of Jupiter, Europa, and Io is transformed into a science fiction setting.
With piercing eyes, a scaly forehead, nostrils, teeth, and even curling wisps of smoke escaping its mouth, this Jovian dragon could be the stalwart guardian of our lonely solar system. This dragon was born from a JunoCam image containing one pearly white oval storm and a few stripes that was rotated, color enhanced, and mirrored down the center to create a mythical dragon out of Earth’s largest sibling.
Throughout the span of its approximately 2-year mission, Juno will make 32 polar orbits around the planet, skimming within 5,000 kilometers of the cloud tops. What new artistic pursuits will its journey inspire? We can’t wait to find out!
—Kimberly M. S. Cartier (@AstroKimCartier), News Writing and Production Intern
Editor’s Note: We are delighted to bring the GeoFIZZ column back to Eos! | 0.900227 | 3.335495 |
Planets orbiting sun-like stars inside a crowded cluster of stars have been spotted for the first time, by researchers from NASA. This is the best evidence found yet that planets can form in dense star-filled areas. The skies of the newfound planets would have exponentially more stars, and be considerably brighter than what we see from Earth.
“The starry-skied planets are two so-called hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different sun-like star in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center,” a news release from NASA stated.
An open cluster, the Beehive is a group of stars that were all born around the same time and all formed from the same massive cloud of material. Therefore, the stars and any potential planets share a very similar chemical make-up. And in contrast to most stars, which rapidly spread out and cover a lot of territory soon after birth, these stars continue to be loosely integrated by a common gravitational attraction.
“We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters,” said Mario R. Perez, the NASA astrophysics program scientist in the Origins of Solar Systems Program. “Our galaxy contains more than 1,000 of these open clusters, which potentially can present the physical conditions for harboring many more of these giant planets.”
The news release adds: “The two new Beehive planets are called Pr0201b and Pr0211b. The star’s name followed by a “b” is the standard naming convention for planets.”
“These are the first ‘b’s’ in the Beehive,” said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper.
“Quinn and his team, in collaboration with David Latham at the Harvard-Smithsonian Center for Astrophysics, discovered the planets by using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory near Amado, Arizona to measure the slight gravitational wobble the orbiting planets induce upon their host stars. Previous searches of clusters had turned up two planets around massive stars but none had been found around stars like our sun until now.”
“This has been a big puzzle for planet hunters,” Quinn said. “We know that most stars form in clustered environments like the Orion nebula, so unless this dense environment inhibits planet formation, at least some sun-like stars in open clusters should have planets. Now, we finally know they are indeed there.”
“The results also are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theories contend these blistering worlds start out much cooler and farther from their stars before migrating inward.”
“The relatively young age of the Beehive cluster makes these planets among the youngest known,” said Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded this study. “And that’s important because it sets a constraint on how quickly giant planets migrate inward — and knowing how quickly they migrate is the first step to figuring out how they migrate.”
It is presumed by the research team that the Beehive cluster included the planets because of its abundance of metals. “Stars in the Beehive have more heavy elements such as iron than the sun has.”
White said: “Searches for planets around nearby stars suggest that these metals act like a ‘planet fertilizer,’ leading to an abundant crop of gas giant planets. Our results suggest this may be true in clusters as well.”
The research was just published in the Astrophysical Journal Letters.
Source: NASA/Jet Propulsion Laboratory
Image Credits: NASA/JPZl-Caltech | 0.913222 | 3.811442 |
The photosphere is the visible "surface" of the Sun (left). Sunspots are often visible "on" the photosphere. A close-up view (right) shows the granulation pattern on the photosphere.
Click on image for full size
Images courtesy of SOHO/NASA/ESA and The Royal Swedish Academy of Sciences and Oddbjorn Engvold, Jun Elin Wiik, and Luc Rouppe van der Voort - University of Oslo.
The Photosphere - the "Surface" of the Sun
Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest
regions of the Sun (6000 K), so only a small fraction (0.1%) of the gas is
ionized (in the plasma state). The photosphere is the densest
part of the solar atmosphere, but is still tenuous compared to
Earth's atmosphere (0.01% of the mass density of air at sea level).
The photosphere looks somewhat boring
at first glance: a disk with some dark spots. However, these
are the site of strong magnetic fields. The solar magnetic field is believed to drive the complex
activity seen on the Sun.
Magnetographs measure the solar magnetic field at the photosphere.
Because of the tremendous heat coming from the solar core, the solar interior below
the photosphere (the convection zone) bubbles like a pot of boiling water.
The bubbles of hot material welling up from below are seen at the photosphere
as slightly brighter regions. Darker regions occur where cooler plasma
is sinking to the interior. This constantly churning pattern of convection
is called the solar granulation pattern.
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On March 30, 1998, the TRACE spacecraft will be launched. TRACE stands for Transition Region and Coronal Explorer (try saying that fast three times!). This spacecraft has four telescopes on it. The telescopes...more | 0.802926 | 3.914599 |
This replica model of ESA’s ‘Miniaturised Asteroid Remote Geophysical Observer’, or M-Argo, was on display at the Agency’s recent Antennas workshop. It is the one of numerous small missions planned as part of in ESA’s Technology Strategy, being presented at this month’s Space19+ Council at Ministerial Level.
This is a suitcase-sized nanospacecraft based on the CubeSat design employing standardised 10 cm cubic units within which electronic boards can be stacked and subsystems attached. M-Argo is a 12-unit CubeSat – with a 22 x 22 x 34 cm body – that would hitch a ride on the launch of a larger space mission whose trajectory takes it beyond Earth orbit, such as astronomy missions to a Sun–Earth Lagrange point.
The CubeSat would then use its own miniaturised electric thruster to take it into deep space and rendezvous with an asteroid, which it would survey using a multispectral camera and a laser altimeter to look for resources such as hydrated minerals that could be extracted in future. Other miniaturised payloads are also being considered.
“Such a small spacecraft has never independently travelled through deep space to rendezvous with an asteroid before,” comments Roger Walker, overseeing ESA’s Technology Cubesats. “It will enable the cost of asteroid exploration to be reduced by an order of magnitude or more.”
Numerous miniaturised technologies are currently being developed to enable the M-Argo mission, including the electric propulsion system, a high frequency ‘X-band’ communications system with a flat panel antenna – as seen in the image – to communicate with Earth at distances of up to 150 million km and a mechanism to steer the solar panels constantly at the Sun to generate enough power for the electric propulsion and communications systems.
“The team has identified a total of 148 near-Earth asteroids potentially reachable for a rendezvous using design,” adds Roger. “From these, five different asteroids have been carefully selected for further analysis in terms of optimising their rendezvous trajectories and close-up navigation – some of the closest to Earth in terms of the amount of fuel needed to get there: a key consideration for future mining of in-situ resources.
“M-Argo design has recently reached a milestone with the Mission Definition Review, which confirms that the CubeSat can rendezvous with any one of these five different asteroids, if launched during the 2023-2025 timeframe. The M-Argo team will now focus on completing the design concept of the CubeSat up until April next year. ”
“This is the first time ESA is designing a low-cost spacecraft for asteroid mining purposes in line with the Luxembourg space strategy. M-Argo and numerous other innovative technology-testing CubeSat missions, are being supported through the Fly element of the Agency’s General Support Technology Programme, part of ESA’s Technology Strategy being presented at Space19+.” says Kenza Benamar, Coordinator of the Fly element.
Also being presented at the Ministerial is the Hera asteroid mission, a larger-scale spacecraft that would deploy two CubeSats when it reaches its target binary asteroid system. | 0.828526 | 3.017156 |
THE DETAILS: Over the course of the decades since the Apollo crewed landings, the Moon has been visited and mapped in progressively greater detail by uncrewed probes sent by China, India, Japan and the United States. Some of these spacecraft are currently in operation in orbit around the Moon, sending fresh images and science data.
Many of these spacecraft carried telescopes and cameras, but these instruments were not powerful enough to show directly the vehicles left behind by the Apollo astronauts. However, they were able to acquire evidence of their presence. Three probes of three separate countries have photographed the differently-colored patch of lunar soil produced by the landing of Apollo 15. The Lunar Reconnaissance Orbiter was the first probe equipped with instruments that were capable of directly imaging in detail the Apollo vehicles.
Clementine (United States, 1994)
The 1994 Clementine probe, launched by NASA, spent 71 days orbiting the Moon to map its surface at various wavelengths, from ultraviolet to near infrared, and with a laser altimeter. The images acquired by this probe included the one shown in Figure 7.7-1, which features a dark patch of differently reflective soil exactly where NASA said that Apollo 15’s LM had landed. This patch is compatible with the soil color changes expected as a consequence of the displacement of surface dust and the exposure of differently-colored underlying rock that would be caused by a spacecraft rocket motor.
Figure 7.7-1. The dark patch marked by the letter A is located exactly where Apollo 15 landed. B and C are broader patches, probably caused by meteor impacts. This image was acquired using non-visible wavelengths and therefore the shades of gray do not necessarily match visible-light colors.
The Apollo 15 dust displacement was discovered in 2001 by Misha Kreslavsky of the department of geological sciences at Brown University (Rhode Island, United States) and by Yuri Shkuratov of the Kharkov Astronomical Observatory in Ukraine while they were studying lunar surface color changes produced by recent meteor impacts, which displace the soil.*
* Apollo 15 Landing Site Spotted in Images, di Leonard David, Space.com, 27 aprile 2001.
Kàguya/SELENE (Japan, 2007-2009)
As it explored the Moon from orbit at an altitude of approximately 100 kilometers (62 miles), the Japanese probe Kaguya detected a differently-colored patch of lunar soil exactly where NASA said that Apollo 15 had landed (Figure 7.7-2). This finding, like Clementine’s, is compatible with the color changes expected due to dust displacement by a landing rocket motor.
Figure 7.7-2. This visible-light image, published on 20 May 2008, shows a brighter patch right where Apollo 15 landed. Credit: JAXA/Selene.
The Kaguya probe also acquired very accurate terrain contour maps of the landing sites, which exactly match the terrain shown in the Apollo photos, as described in Chapter 3.
Chandrayaan-1 (India, 2008-2009)
The Indian probe Chandrayaan-1 orbited around the Moon about 3400 times at an altitude of 100 kilometers (62 miles) to perform a chemical, mineralogical and geological survey. It carried scientific instruments from India, the United States, the United Kingdom, Germany, Sweden and Bulgaria.
Like Clementine and Kaguya, Chandrayaan-1 acquired images showing a brighter patch at the Apollo 15 landing site, but it did better than its predecessors: it deteced a faint dot at the location of the descent stage o the Lunar Module (Figure 7.7-3).
Figure 7.7-3. Images of the Apollo 15 landing site acquired by the three cameras of the Indian Chandrayaan-1 probe on 9 January 2009 (a = rear camera; b = nadir camera; c = front camera. Source: Chandrayaan-1 captures Halo around Apollo-15 landing site using stereoscopic views from Terrain Mapping Camera by Prakash Chauhan, Ajai and A.S.; Kirankumar, in Current Science vol. 97, no. 5, 10 September 2009, p. 630-31.
Lunar Reconnaissance Orbiter (USA, 2009-)
The United States’ Lunar Reconnaissance Orbiter (LRO) probe was the first spacecraft equipped with instruments capable of directly imaging the Apollo vehicles left on the Moon. It achieved this result as part of its ongoing lunar mapping mission.
Its first images of the Apollo landing sites were published on 17 July 2009 and some of them are shown in Chapter 3.
Figure 7.7-4. Images of the six Apollo landing sites acquired by the Lunar Reconnaissance Orbiter (2009-).
Chang’e-2 (China, 2010-2011)
China has sent several probes to the Moon. In 2010, its Chang’e-2 spacecraft mapped the Moon from an altitude which varied between 15 and 100 kilometers (9.3 and 62 miles), with a maximum resolution of 7 meters (23 feet). According to a statement made in 2012 by Yan Jun, chief application scientist of the Chinese lunar exploration program, Chang’e-2 “spotted traces of the previous Apollo mission in the images”. However, the imagery has not been released.
Images of Apollo hardware crash sites on the Moon
In addition to the actual landing sites, there are other traces of these missions on the Moon. The ascent stages of the Lunar Modules of Apollo 12, 14, 15, 16 and 17, and the third stages of Apollo 13, 14, 15, 16 and 17 were deliberately crashed on the Moon. Many of these crash sites have been imaged from orbit by the Lunar Reconnaissance Orbiter, showing patterns of debris that support NASA’s claims.*
* Spacecraft Impacts on the Moon: Chang’e 1, Apollo LM Ascent Stages in Lunar and Planetary Science XLVIII (2017); Impact Sites of Apollo LM Ascent and SIVB Stages, NASA; The Crash Site of Apollo 16's Rocket Booster Has Been Spotted on The Moon, Sciencealert.com (2015).
Figure 7.7-5. Images of the Apollo 16 third stage crash site on the Moon. Credit: NASA/Goddard/Arizona State University. Source: Space.com. | 0.80371 | 3.717988 |
Taipan is an ambitious survey planned for southern hemisphere galaxies, with the goal of mapping and measuring as many as one million galaxies in our Milky Way’s neighborhood. This will provide a deeper understanding of cosmology and galaxy evolution in the relatively nearby region of our universe.
There are more than a hundred billion galaxies in our visible universe. In order to refine our understanding of galaxies, their distribution and evolution, and of the overall cosmological properties of the universe, we want to sample a very large number of galaxies.
It is naturally easier to detect galaxies that are relatively nearby, and those that are more luminous.
Since the universe is expanding in an isotropic and homogeneous manner, galaxies are in general receding away from one another – in accordance with the Hubble relation below. The Taipan survey will explore our local neighborhood, with redshifts up to about 0.3.
For nearby galaxies,
V = cz = H*d
where V is the recession velocity, c is the speed of light, z is the redshift, H is the Hubble constant, and d is the galaxy’s distance. If we evaluate for z = 0.3 and the best estimate of the Hubble constant of 68 kilometers/second/Megaparsec, this implies a survey depth of 1300 Megaparsecs, or over 4 billion light-years.
The Taipan galaxy survey will begin next year and run for four years, using the UK Schmidt telescope, which is actually in Australia at the Siding Springs Observatory. Up to 150 galaxies in the field of view will be observed simultaneously with a fibre optic array. Of course the positions of galaxies is different in each field to be observed, so the fibers are robotically placed in the the proper positions. Many thousands of galaxies can thus be observed each night.
Short video of a Starbug fiber robot
One expected result will be refinement of the value of the Hubble constant, now uncertain to a few percent, reducing its uncertainty to only 1%.
The Taipan galaxy survey will also provide a better constraint on the growth rate of structure in the universe, decreasing the uncertainty down to about 5% for the low-redshift data points. This is a factor of 3 improvement and will provide a stricter test on general relativity.
The Taipan survey will also look at galaxies’ peculiar velocities, which are the deviations away from the general Hubble flow described in the equation above. These peculiar velocities reflect the details of the gravitational field – that is dominated by the distribution of dark matter primarily, and ordinary matter secondarily. On average galaxies are moving according to the Hubble equation, but in regions where the density of matter (dark and ordinary both) is higher than average they are pulled away from the Hubble flow toward any concentrations of matter. Bound galaxy groups and clusters form in such regions.
The mapping of peculiar velocities and the details of local variations in the gravitation field will enable fundamental tests of gravity on large scales.
Another of the important areas that Taipan will explore is how galaxies evolve from young active star-forming blue galaxies to older reddish, less active galaxies. Ordinary matter cycles through stars and the interstellar medium of a given galaxy. As stars die they shed matter which ends up in molecular clouds that are the sites of new star formation. Taipan will help to increase our understanding of this cycle, and of galaxy aging in general. Star formation slows down as more and more gas is tied up in lower mass, longer-lived stars, and the recycling rate drops. It also can be quenched by active galactic nuclei events (AGN are powered by supermassive black holes found at galactic centers).
Taipan will be the definitive survey of galaxies in the southern hemisphere, and is expected to significantly add to our understanding of galaxy evolution and cosmology. We look forward to their early results beginning in 2016. | 0.88975 | 4.00986 |
"Mars-3" inter-planetary station in the assembly shop, Moscow, 1971. Source: B. Borisov / TASS
A group of scientists and space enthusiasts from Russia is trying to figure out where the remnants of Soviet spacecraft Mars-6 are. They’ve already managed, thanks to the help of NASA satellites, to unearth where Mars-3 is.
This probe was the first spacecraft to successfully accomplish a landing on the Red Planet. The group is also going to search for the first Soviet mission on Mars, the Mars-2 probe, which was launched in May 1971. The spacecraft crashed during landing, but it became the first artificial object to land on Mars. According to scientists, studying these spacecrafts will help humankind in its conquest of the planet.
A few years ago space enthusiast Vitaly Egorov was surprised to learn that the location of the Soviet probes Mars-6 and Mars-2 still remains a mystery. Nobody had ever seen the Mars-3 spacecraft either. The latter had been the protagonist of a phenomenal achievement, the first successful landing of a spacecraft on Mars in December 1971.
The spacecraft ceased to transmit data just 14.5 seconds after landing. Although it only managed to transmit a panorama of the surrounding surface, it demonstrated that a successful landing on Mars was possible. “Over 40 years ago Mars-3 accomplished a landing almost in the same sequence as the American spacecraft Curiosity in 2012,” says Egorov.
Egorov began his search for the lost Soviet spacecrafts with the aid of pictures taken by the NASA Mars Reconnaissance Orbiter (MRO) scientific satellite. The latter is equipped with a high resolution HiRise camera.
“We accept image suggestions from anyone in the world at our website,” Alfred S. McEwen, director of the Planetary Image Research Laboratory of the University of Arizona and manager of the MRO HiRise scientific team, told RIR.
Egorov assembled group of bloggers, space enthusiasts and scientists that discovered an object similar to a Soviet space probe in the shots taken by the MRO. He contacted Alexander Bazilevsky, a professor at the Vernadsky Institute of Geochemistry and Analytical Chemistry.
Thanks to his support, in March 2013 NASA organized another photo session with the MRO. In the pictures they could clearly identify an overturned axis with soft landing engines, the cone brake, the parachute and the landing module, which measured 1.5 meters. There were no doubts that it was the Mars-3 space probe.
'The atmosphere on Mars is variable'
Now the group set up by Egorov is trying to find out where Mars-6 is. The spacecraft entered the atmosphere of Mars in 1974. Immediately after landing it ceased all transmissions. According to one version, the breakdown was caused by a Martian storm that caught the probe while its soft landing engines were being started.
“According to the telemetry data, the spacecraft opened its parachute,” Egorov says. “We have been trying to find it, but so far to no avail. In the pictures that we have, we have noticed some dots that might have been produced by a descending module, but so far we have not gathered enough supporting evidence. We are waiting for new pictures of the area where the spacecraft presumably landed.”
According to McEwen, the study of the photographs taken by Mars-3 and Mars-6 helps scientists to understand the reasons for the troubles experienced by Soviet hardware.
“Any new high-resolution image may tell us something new and important about Mars,” says McEwen.
“An image of the old Soviet landing hardware can also provide information to the engineers about what did and did not work correctly.”
“From the pictures we can even determine the extent to which these Soviet spacecrafts have been covered by sand or dust,” Bazilevsky told RIR. “This is one of the ways we have to study the atmosphere of the Red Planet, which is important for the construction of a future station on Mars. That planet’s atmosphere is so variable with periodic storms and strong winds, unlike the Moon where the traces of lunar spacecraft can remain intact for thousands of years.”
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The vastness of the universe and beauty of deep space is truly break-taking and awe-inspiring, take a look at 10 images taken by Hubble Space Telescope and be astounded.
1) Westerlund 2
This NASA/ESA Hubble Space Telescope image of the cluster Westerlund 2 and its surroundings has been released to celebrate Hubble’s 25th year in orbit and a quarter of a century of new discoveries, stunning images and outstanding science. The image’s central region, containing the star cluster, blends visible-light data taken by the Advanced Camera for Surveys and near-infrared exposures taken by the Wide Field Camera 3. The surrounding region is composed of visible-light observations taken by the Advanced Camera for Surveys.
2) Sombrero Galaxy
NASA/ESA Hubble Space Telescope has trained its razor-sharp eye on one of the universe’s most stately and photogenic galaxies, the Sombrero galaxy, Messier 104 (M104). The galaxy’s hallmark is a brilliant white, bulbous core encircled by the thick dust lanes comprising the spiral structure of the galaxy. As seen from Earth, the galaxy is tilted nearly edge-on. We view it from just six degrees north of its equatorial plane. This brilliant galaxy was named the Sombrero because of its resemblance to the broad rim and high-topped Mexican hat. At a relatively bright magnitude of +8, M104 is just beyond the limit of naked-eye visibility and is easily seen through small telescopes. The Sombrero lies at the southern edge of the rich Virgo cluster of galaxies and is one of the most massive objects in that group, equivalent to 800 billion suns. The galaxy is 50,000 light-years across and is located 30 million light-years from Earth.
3) Ring Nebula
This new image shows the dramatic shape and colour of the Ring Nebula, otherwise known as Messier 57. From Earth’s perspective, the nebula looks like a simple elliptical shape with a shaggy boundary. However, new observations combining existing ground-based data with new NASA/ESA Hubble Space Telescope data show that the nebula is shaped like a distorted doughnut. This doughnut has a rugby-ball-shaped region of lower-density material slotted into in its central “gap”, stretching towards and away from us.
4) Pillars of Creation
The NASA/ESA Hubble Space Telescope has revisited one of its most iconic and popular images: the Eagle Nebula’s Pillars of Creation. This image shows the pillars as seen in visible light, capturing the multi-coloured glow of gas clouds, wispy tendrils of dark cosmic dust, and the rust-coloured elephants’ trunks of the nebula’s famous pillars. The dust and gas in the pillars is seared by the intense radiation from young stars and eroded by strong winds from massive nearby stars. With these new images comes better contrast and a clearer view for astronomers to study how the structure of the pillars is changing over time.
5) Flocculent Spiral of NGC 2841
Star formation is one of the most important processes in shaping the Universe; it plays a pivotal role in the evolution of galaxies and it is also in the earliest stages of star formation that planetary systems first appear. Yet there is still much that astronomers don’t understand, such as how do the properties of stellar nurseries vary according to the composition and density of gas present, and what triggers star formation in the first place? The driving force behind star formation is particularly unclear for a type of galaxy called a flocculent spiral, such as NGC 2841 shown here, which features short spiral arms rather than prominent and well-defined galactic limbs.
6) Monkey Head Nebula (NGC 2174)
To celebrate its 24th year in orbit, the NASA/ESA Hubble Space Telescope has released this beautiful new image of part of NGC 2174, also known as the Monkey Head Nebula. NGC 2174 lies about 6400 light-years away in the constellation of Orion (The Hunter). Hubble previously viewed this part of the sky back in 2011 — the colourful region is filled with young stars embedded within bright wisps of cosmic gas and dust. This portion of the Monkey Head Nebula was imaged in the infrared using Hubble’s Wide Field Camera 3.
7) Messier 100 Spiral Galaxy
This stunning spiral galaxy is Messier 100 in the constellation Coma Berenices, captured here by the NASA/ESA Hubble Space Telescope — not for the first time. Among Hubble’s most striking images of Messier 100 are a pair taken just over a month apart, before and after Servicing Mission 1, which took place 25 years ago in December 1993. After Hubble was launched, the astronomers and engineers operating the telescope found that the images it returned were fuzzy, as if it were out of focus. In fact, that was exactly what was happening. Hubble’s primary mirror functions like a satellite dish; its curved surface reflects all the light falling on it to a single focal point. However, the mirror suffered from a defect known as a spherical aberration, meaning that the light striking the edges of the mirror was not travelling to the same point as the light from the centre. The result was blurry, unfocused images. To correct this fault, a team of seven astronauts undertook the first Servicing Mission in December 1993. They installed a device named COSTAR (Corrective Optics Space Telescope Axial Replacement) on Hubble, which took account of this flaw of the mirror and allowed the scientific instruments to correct the images they received. The difference between the photos taken of Messier 100 before and after shows the remarkable effect this had, and the dramatic increase in image quality. COSTAR was in place on Hubble until Servicing Mission 4, by which time all the original instruments had been replaced. All subsequent instrumentation had corrective optics built in. This new image of Messier 100 taken with Hubble’s Wide Field Camera 3 (WFC3), demonstrates how much better the latest generation of instruments is compared to the ones installed in Hubble after its launch and after Servicing Mission 1. Links Messier 100 shows improvements of Hubble Messier 100 seen 1993 with WFPC1 Messier 100 seen 1994 with WFPC2
8) Storms of Jupiter
This image of Jupiter was taken when the planet was at a distance of 670 million kilometres from Earth. The NASA/ESA Hubble Space Telescope reveals the intricate, detailed beauty of Jupiter’s clouds as arranged into bands of different latitudes. These bands are produced by air flowing in different directions at various latitudes. Lighter coloured areas, called zones, are high-pressure where the atmosphere rises. Darker low-pressure regions where air falls are called belts. Constantly stormy weather occurs where these opposing east-to-west and west-to-east flows interact. The planet’s trademark, the Great Red Spot, is a long-lived storm roughly the diameter of Earth. Much smaller storms appear as white or brown-coloured ovals. Such storms can last as little as a few hours or stretch on for centuries.
This Hubble image gives the most detailed view of the entire Crab Nebula ever. The Crab is among the most interesting and well studied objects in astronomy. This image is the largest image ever taken with Hubble’s WFPC2 camera. It was assembled from 24 individual exposures taken with the NASA/ESA Hubble Space Telescope and is the highest resolution image of the entire Crab Nebula ever made.
Centaurus A, also known as NGC 5128, is well known for its dramatic dusty lanes of dark material. Hubble’s new observations, using its most advanced instrument, the Wide Field Camera 3, are the most detailed ever made of this galaxy. They have been combined here in a multi-wavelength image which reveals never-before-seen detail in the dusty portion of the galaxy. As well as features in the visible spectrum, this composite shows ultraviolet light, which comes from young stars, and near-infrared light, which lets us glimpse some of the detail otherwise obscured by the dust. | 0.88882 | 3.500998 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2009 November 22
Explanation: What caused this outburst of V838 Mon? For reasons unknown, star V838 Mon's outer surface suddenly greatly expanded with the result that it became the brightest star in the entire Milky Way Galaxy in January 2002. Then, just as suddenly, it faded. A stellar flash like this has never been seen before -- supernovas and novas expel matter out into space. Although the V838 Mon flash appears to expel material into space, what is seen in the above image from the Hubble Space Telescope is actually an outwardly moving light echo of the bright flash. In a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star. V838 Mon lies about 20,000 light years away toward the constellation of the unicorn (Monoceros), while the light echo above spans about six light years in diameter.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | 0.914699 | 3.096501 |
Some missions requires to change velocities of the satellite after its detaching from the launcher. The satellites propulsion systems give to spacecrafts possibility to make maneuvers for different purpose e.g transfer to target obit, station keeping, collision avoidance, decommissioning.
Propulsion based on Newton third principle
For every action, there is an equal and opposite reaction – classical propulsion systems utilze this Newtons principle. The engines expel mass in one direction to produce thrust in opposite direction.
Thrust force and impulse
Two properties characterize classical propulsion system: thrust force in Newton or pounds and impulse. Impulse is a measure which tells us how fast propellant is consumed to produce thrust. In mathematical terms:
Solid fuel propulsion systems
Solid rocket fuel is filled with mixture of relatively hard, rubbery, combustible mixture of fuel, oxidizer and binder. Engine is ignited by pyrotechnic device – igniter. Engine usually contains two igniters to have redundancy.
The combustible mixture when ignited burns very rapidly, producing a intense thrust, which can reach . The engine produce impulse about 300s. Solid fuel motor is suitable for major orbital manoeuvres such as apogee or perigee kick operations. The motor can be attached to the bottom of the spacecraft and detached after use, or integrated inside the spacecraft body.
The example is a motor of Voyager spacecraft, which weighed 1,123 kg including 1,039 kg of propellant, developed an average 6,805,440 N thrust during its 43-second burn duration. It was used for reach final Jupiter trajectory velocity. The motor was jettisoned after burnout its propellant.
Liquid fuel propulsion systems
Liquid propellant motors can by classified as monopropellant and bipropellant
Monopropellant solution uses a single combustible propellant like hydrazine, which on contact with catalyst decomposes into its constituents what produce energy and thrust. It gives thrust in range 0.05N to 0,25N and specific impulse 200s. These kind of engines are used for smaller orbital maneuvers such as station keeping.
Bipropellant engine uses separated tanks for fuel and oxidizer. In the combustion chumber fuel and oxidizer are mixed. This kind of engine produce a greater thrust for the same weight of fuel. The examples of fuel-oxidizer combinatos are kerosene-liquid oxygen, liquid hydrogen-oxygene, hydrazine-nitrogen tetraoxide. The engines produce thrust up to \(\)10^6N\(\) and have impulse 300-400s. Bipropellant engines are used to major orbital changes requairing large amount of thrust.
Good example of use liquid fuel by spacecraft is a Cassini – Saturns’ orbiter. For major orbital changes it used bipropellant engine ( exactly it had two main engines, includes spare), and for positioning maneuvers monopropelant thrusters.
Cold gas propultion systems
Relatively simply is a engine which uses gas at high pressure which fed to a number of small thrusters. Kinetic energy of the nozzle exhaust is solely determined by the driving pressure in the reservoir. Typically gases are nitrogen, argon, freon, propane. Propellant are selected for the simplicity of their storage and its indifference to spacecrafts’ materials which can be hit by exhaust plume. The thrust levels are low (~10mN), and the impulse is comparatively small: ~50s. This kind of propulsion system is used to attitude control and station keeping of small satellites like nano-satellites, cubesats.
Electric propulsion systems
There is a set of propulsion system which use electricity to accelerate expellant. Electric power may be used to heat up propellant, to interacts with propellant ions or to use electromagnetic field to induce a Lorenz force on plasma.
The simplest powered by electricity propulsion systems accelerate expellant by heats up the propellant. The typically propellants are hydrogen, nitrogen, ammonia and hydrazine. We can distinguish two kinds of electrothermal engines:
- Resistojet: closely allied to chemical propulsion, ohmic heating caused by an electric current through a heater raises the temperature of the propellant stream, then the hot exhaust gas is accelerated aerodynamically in a nozzle. The performance of this type of limited by the properties of the propellant, temperature that can be attained in the thruster. The example is an power-augmented hydrazine thruster (PAEHT).
- Arcjet: propellant is heated by electric arc, which it passes through on its way to exhaust nozzle. The engnines use electric power in the range of 1KW to 20KW, and is capable to produce specific impulse in the range of 500s to 800s with thrust an order of magnitude smaller than monopropellant hydrazine liquid thruster.
Thrust is produced by accelerating positivly charged particles in a intense electrical field. The stream of positivly charged particles must be neutralized to avoid a charge, opposite to that carried away from the spacecraft in the beam. The engine carries very little fuel and relies on acceleration of charged particles to a heigh velocity.
- Ion thruster with elementary gas as a propellant can producing impulse of the order 3000s at an electical power 1KW. Gas is ionized by electrons emited from an axially mounted thermiodic cathode towards a concentric cylindrical anode.
- Ion thruster with acceleration of charged fluid droplets can generates thrust bigger than engines with ionized gas, but have lower impulse. Inside the engine fluid cone is formed and breaks up into a fine spray of pisitively charged droplets.
Some engines use magnetic field together with electricity to accelerate propellant.
The one of the example is an engine which utilize Hall effect. This kind of engine was developed in former Soviet Union. In ‘Hall effect engines’ high voltage accelerates ions of a propellant (gas xenon, krypton,argon, bismuth, iodine, magnesium or zinc). Additionally radial magnetic field interacts with electrons, holds them for a while inside engine and creates from them Hall current. A large number of high energetic electrons which stay inside engine effectively ionize the gas, so almost all of its mass is accelerated by the electric field (even 90%-99% of the gas become ionized). The engine have big impulse (2500s) and thrust about 500mN. SpaceX Starlink satellites use ‘Hall efect engines’.
In The magnetplasmadynamic arc jet both Joule heating and electrodynamic forces accelerate neutral plasma. The self-induced magnetic field provides the dominant acceleration mechanism.
Solar sail propultion
The Sun emits radiation, which can be reflected by mirror sails, and thus the sail will produce a thrust. Additionaly energy of the solar wind can by utilized. The possibility of of using Suns’ emmision pressure has been seriosly discussed since 1924, when Friedrich Zander publicate technical paper.
The problem is the size of the sail, which must be very big, for example to get thrust about 5N near The Earth, the sail will need to have size 800x800m.
The realistic and usefuly application have appeared with starting age of small satellites. Small satellites with low masses can use solar sail for different manevrous, especialy to speed up deorbitation. The examples of projects are PWSAT and Light Sail. Japanese mission IKAROS successfully demonstrated solar sail technology in interplanetary space.
- 2014) Satellite Technology: Principles and Applications, third Edition. Wiley, United Kingdom. (
- 2018) Low Earth Orbit Satellite Design. Springer, Switzerland. (
- 1978) Solar Sailing-The Concept Made Realistic. (
- 1980) ‘Voyager Backgrounder’ [online]. Available at: <https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810001583.pdf>. Accessed: 15.09.2019 (
- 2011) Spacecraft Systems Engineering 4th Edition. Wiley, . (
- Electric propulsion for Small Spacecraft’ [online]. Available at: <https://digitalcommons.usu.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=2586&context=smallsat>. Accessed: 25.09.2019 () ‘ | 0.847747 | 3.029233 |
New Horizons spurs new calls to make Pluto a planet once again
After nearly a decade in the wilderness of celestial classification, Pluto is on the rise again. In 2006, the International Astronomical Union (IAU) voted to adopt a new definition of what makes a body a planet, and to specifically demote Pluto to the status of dwarf planet. Now, with new data and images streaming in from New Horizons showing that Pluto is not only a little larger than previously thought, but also home to some remarkable geological features (including what may be some of the solar system's youngest mountain peaks, reaching to 11,000 ft/3,353 m high), many are saying it's time to restore the ninth planet to its previous station.
Perhaps not surprisingly, some of the most prominent advocates for Pluto are scientists working on the New Horizons mission, which reached the closest point of its long-awaited Pluto fly-by on July 14.
"We are free to call it a planet right now," Philip Metzger, a planetary scientist on the New Horizons mission, told DW.com. "Science is not decided by votes ... the planetary science community has never stopped calling bodies like Pluto 'planets'."
Indeed, science – like journalism – is not a democratic process, which tends to make it a little messy at times. But for the sake of standardization and communication, we all cut corners now and then by agreeing to imperfect definitions of concepts. This lets us avoid constantly having to refer to things like Pluto in terms such as "an object possessing many traditional qualities ascribed to planets but also sporting more anomalous characteristics, like its sharing of an orbital centerpoint with its moon Charon and lying in a region of deep space occupied by trans-Neptunian objects likely originating from the nearby Kuiper Belt."
The real trouble for Pluto arguably started with the 2005 discovery of Eris. Eris is one of those aforementioned trans-Neptunian objects (things that orbit the sun from a point beyond Neptune, on average) that was thought to be significantly larger than Pluto. If Pluto is a planet, then surely larger Eris must be a planet, and if things smaller than Eris like Pluto are planets, then there could literally be hundreds of trans-Neptunian objects deserving of being added to the family of planets.
For whatever reason, be it the chaos of rewriting countless astronomy textbooks or a hidden lobby favoring preservation of an elevated status for gas giant planets within the IAU, the body voted instead to basically demote all potential planets orbiting in the more crowded stretches of the solar system – notably the asteroid belt between Mars and Jupiter, and the Kuiper Belt beyond Neptune – to dwarf planet status or something lesser.
It should be noted, however, that this 2006 vote was relatively close. In the end, 237 astronomers voted to officially demote Pluto, 157 voted against the measure and 17 abstained. The vote to define a planet as a body orbiting the sun that has a nearly round shape and has "cleared the neighborhood around its orbit" was not nearly as close, though. And even with the remarkable new data coming back from New Horizons' cruise by Pluto, which seems to show that it is actually bigger than Eris after all, it still does not meet the third criterion for once again being named a planet under the IAU's current definition.
In fact, it was Eris' discoverer Mike Brown who became one of the villains in the eyes of Pluto proponents following the 2006 vote, but today he still says the demotion was the right thing to do.
Still, some Pluto enthusiasts see it as fortuitous that New Horizons' much-hyped encounter has taken place just weeks before the next general assembly of the IAU, which only happens once every three years and is set to take place this August in Hawaii. At the moment, Pluto is not on the IAU agenda next month, but that hasn't stopped Hollywood director Paul Feig – director of Spy, Bridesmaids and the upcoming Ghostbusters reboot - from starting a petition on Change.org to pressure the IAU to reconsider returning the planet count to nine.
"In the coming weeks, New Horizons will collect unprecedented amounts of data about the Pluto system, calling in to question the definition set forth by the IAU," the petition reads.
Others aren't waiting for the IAU to change its mind. If Pluto has a hometown, it might as well be Alamogordo, New Mexico, home to the Museum of Space History and just down the road from New Mexico State University, where Pluto's discoverer, Clyde Tombaugh, was a longtime professor. The town held a "Pluto-palooza" party to celebrate the New Horizons fly-by earlier this month, where the mayor was on hand to declare Pluto a planet once again.
New Horizons mission leader Alan Stern is also on record saying the planet definition "stinks" and his colleague Metzger certainly supports the view of Alamogordo over the IAU when it comes to Pluto. "Start calling Pluto a planet right now. Add to the consensus, because that's how science makes progress, by one person at a time being convinced of the truth and adopting it," Metzger says. "You are not required to submit to nonsense." | 0.919978 | 3.293754 |
In what is being hailed as a "groundbreaking discovery", astronomers have for the first time observed two supermassive black holes orbiting around each other in a distant galaxy, according to new research.
In an article published in the Astrophysical Journal, researchers have detailed how they used radio telescopes to detect what appeared to be two black holes moving in relation to each other in radio galaxy 0402+379 .
"For a long time, we've been looking into space to try and find a pair of these supermassive black holes orbiting as a result of two galaxies merging," University of New Mexico's professor of physics and astronomy Greg Taylor said.
The research team has been studying the two objects, which lie at the centre of the bulging galaxy, since 2003.
The galaxy itself was discovered in 1995 and is approximately 750 million light years away from Earth.
The lead author of the paper, Karishma Bansal, said the black holes are at a "separation of about seven parsecs," or 217 trillion kilometres.
"[This] is the closest together that two supermassive black holes have ever been seen before," she said.
The black holes are among the largest ever found, with a combined mass 15 billion times that of the sun, the study says.
If confirmed, it will be the smallest ever recorded movement of an object across the sky — at a rate of just over one micro-arc second per year, an angle about 1 billion times smaller than the smallest thing visible with the naked eye.
That means one black hole is believed to be orbiting around the other over a period of 30,000 years, the researchers said.
"If you imagine a snail on the recently discovered Earth-like planet orbiting Proxima Centauri — a bit over four light years away — moving at one centimetre a second, that's the angular motion we're resolving here," Stanford's professor of physics and co-author of the paper, Roger W Romani, said.
The researchers are hoping the finding will offer insight into "how black holes merge, how these mergers affect the evolution of the galaxies around them and ways to find other binary black-hole systems".
Large galaxies often have supermassive black holes at their centre and astronomers argue, if large galaxies combine, their black holes eventually follow suit.
As a result, the researchers have suggested that it is possible the apparent orbit of the black hole in 0402+379 is an "intermediary stage in this process".
But, given how slowly the pair is orbiting, the team thinks the black holes are too far apart to come together within the estimated remaining age of the universe, unless there is an added source of friction, they argue. | 0.800644 | 3.995368 |
A new study suggests that plate tectonics--a scientific theory that divides the earth into large chunks of crust that move slowly over hot viscous mantle rock--could have been active from the planet's very beginning. The new findings defy previous beliefs that tectonic plates were developed over the course of billions of years.
The paper, published in Earth and Planetary Science Letters, has important implications in the fields of geochemistry and geophysics. For example, a better understanding of plate tectonics could help predict whether planets beyond our solar system could be hospitable to life.
"Plate tectonics set up the conditions for life," said Nick Dygert, assistant professor of petrology and geochemistry in UT's Department of Earth and Planetary Sciences and coauthor of the study. "The more we know about ancient plate tectonics, the better we can understand how Earth got to be the way it is now."
For the research, Dygert and his team looked into the distribution of two very specific noble gas isotopes: Helium-3 and Neon-22. Noble gases are those that don't react to any other chemical element.
Previous models have explained the Earth's current Helium-3/Neon-22 ratio by arguing that a series of large-scale impacts (like the one that produced our moon) resulted in massive magma oceans, which degassed and incrementally increased the ratio of the Earth each time.
However, Dygert believes the scenario is unlikely.
"While there is no conclusive evidence that this didn't happen," he said, "it could have only raised the Earth's Helium-3/Neon-22 ratio under very specific conditions."
Instead, Dygert and his team believe the Helium-3/Neon-22 ratio raised in a different way.
As the Earth's crust is continuously formed, the ratio of helium to neon in the mantle beneath the crust increases. By calculating this ratio in the mantle beneath the crust, and considering how this process would affect the bulk Earth over long periods of time, a rough timeline of Earth's tectonic plate cycling can be established.
"Helium-3 and Neon-22 were produced during the formation of the solar system and not by other means," Dygert said. "As such, they provide valuable insight into Earth's earliest conditions and subsequent geologic activity." | 0.830061 | 3.353531 |
On March 22, Comet P/2016 BA14 (Pan-STARRS) flew just 2.2 million miles (3.5 million kilometers) from Earth, making it the third closest comet ever recorded. The last time a comet appeared on our doorstep was in 1770, when Lexell’s Comet breezed by at about half that distance. Through a telescope, comet BA14 looked (and still looks) like a faint star, though time exposures reveal a short, weak tail. With an excellent map and large amateur telescope you might still find it making a bead across the Big Dipper and constellation Bootes tonight through the weekend.
Flyby Comet Imaged by Radar
While normal telescopes show few details, NASA’s Goldstone Solar System Radar in California’s Mojave Desert pinged P/2016 BA14 with radar over three nights during closest approach and created a series of crisp, detailed images from the returning echoes. They show a bigger comet than expected — about 3,000 feet (one kilometer) across — and resolve features as small as 26 feet (8 meters) across.
“The radar images show that the comet has an irregular shape: looks like a brick on one side and a pear on the other,” said Shantanu Naidu, a researcher at NASA’s Jet Propulsion Laboratory. “We can see quite a few signatures related to topographic features such as large flat regions, small concavities and ridges on the surface of the nucleus.”
I honestly thought we’d see a more irregular shape assuming that astronomers were correct in thinking that BA14 broke off from its parent 252P/LINEAR though it’s possible it happened so long ago that the “damage” has been repaired by vaporizing ice softening its contours.
Radar also shows that the comet is rotating on its axis once every 35 to 40 hours. While radar eyes focused on BA14, Vishnu Reddy, of the Planetary Science Institute, Tucson, Arizona, used the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii to examine the comet in infrared light. He discovered its dark surface reflects less than 3% of the sunlight that falls on it. The infrared data is expected to yield clues of the comet’s composition as well.
Comets are exceptionally dark objects often compared to the appearance of a fresh asphalt road or parking lot. They appear bright in photos because seen against the blackness of space, they’re still reflective enough to stand out. Comet 67P/Churyumov-Gerasimenko, still the apple of the orbiter Rosetta’s eye, is similarly dark, reflecting about 4% of sunlight.
What makes comets so dark even though they composed primarily of ice? Astronomers believe a comet grows a dark ‘skin’ both from accumulated dust and irradiation of its pristine ices by cosmic rays. Cosmic rays loosen oxygen atoms from water ice, freeing them to combine with simple carbon molecules present on comets to form larger, more complex and darker compounds resembling tars and crude oil. Dust settles on a comet’s surface after it’s set free from ice that vaporizes in sunlight.
I live in Minnesota, where our annual State Fair features every kind of deep-fried food you can imagine: deep-fried Twinkies, deep-fried fruit, deep-fried bacon and even deep-fried Smores. Just now, I can’t shake the thought that comets are just another deep-fried confection made of pristine, 4.5-billion-year-old ice toasted by eons of sunlight and cosmic bombardment. | 0.866289 | 3.865459 |
In the summer of 2019, a team of astronomers from NASA, the ESA, and the International Scientific Optical Network (ISON) announced the detection of the comet 2I/Borisov. This comet was the only second interstellar visitor observed passed through our Solar System, coming on the heels of the mysterious ‘Oumuamua. For this reason, astronomers from all over the world watched this comet intently as it made its closest pass to the Sun.
One such group, led by Martin Cordiner and Stefanie Milam of NASA’s Goddard Space Flight Center, observed 2I/Borisov using the ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) in the Chilean Andes. This allowed them to observe the gases 2I/Borisov released as it moved closer to our Sun, thus providing the first-ever chemical composition readings of an interstellar object.
Continue reading “Interstellar Comet 2I/Borisov Formed in a Very Cold Environment”
Comet breakups are a timely topic right now. The interstellar comet 2I/Borisov just broke into at least two pieces. And though that comet is speeding out of the Solar System, never to be seen again, most of them don’t leave the Solar System. Most of them orbit the Sun, and return to the inner Solar System again and again.
A new paper examines the potential hazard to Earth from comets that break into pieces. The author makes the case that comet breakups could have had a hand in shaping the ebb and flow of life on Earth. It could happen again.
Continue reading “When Comets Break Up, the Fragments Can Be Devastating If They Hit the Earth”
In 2019, amateur astronomer Gennadiy Borisov discovered a comet, which now bears his name. There’s a long history of amateur astronomers discovering comets, as they approach our inner Solar System on their elongated orbits. But this one was different: it was moving much too fast to be gravitationally bound to the Sun.
It was an interstellar comet. And now, it looks like it has split into two chunks.
Continue reading “Interstellar Comet 2I/Borisov Appears to Have Broken in Half”
Why is there so little nitrogen in Comet 67P/Churyumov-Gerasimenko (67P)? That’s a question scientists asked themselves when they looked at the data from the ESA’s Rosetta spacecraft. In fact, it’s a question they ask themselves every time they measure the gases in a comet’s coma. When Rosetta visited the comet in 2014, it measured the gases and found that there was very little nitrogen.
In two new papers published in Nature Astronomy, researchers suggest that the nitrogen isn’t really missing at all, it’s just hidden in the building blocks of life.
Continue reading “Rosetta Saw the Building Blocks of Life on Comet 67P”
TESS, the Transiting Exoplanet Survey Satellite, has imaged an outburst from the comet 46P/Wirtanen. It caught the outburst in what NASA is calling the clearest images yet of a comet outburst from start to finish. A comet outburst is a significant but temporary increase in the comet’s activity, outside of the normal sunlight-driven vaporization of ices that creates a comet’s coma and tail.
Astronomers aren’t certain what causes them, but a new study based on this observation is shedding some light on them.
Continue reading “NASA’s TESS Watched an Outburst from Comet 46P/Wirtanen”
On August 30th, 2019, astronomers with NASA, the ESA, and the International Scientific Optical Network (ISON) announced the detection of the interstellar comet C/2019 Q4 (2I/Borisov). News of the object was met with a great deal of excitement since it was only the second interstellar object to be detected by astronomers – the first being the mysterious object known as ‘Oumuamua (which astronomers are still unsure about)!
After a lot of waiting and several follow-up observations, 2I/Borisov is about to make its closest approach to Earth. To mark the occasion, a team of astronomers and physicists from Yale University captured a close-up image of the comet that is the clearest yet! This image shows the comet forming a tail as it gets closer to the Sun and even allowed astronomers to measure how long it has grown.
Continue reading “Interstellar Comet Borisov is About to Make its Closest Approach to Earth”
For over a century, proponents of Panspermia have argued that life is distributed throughout our galaxy by comets, asteroids, space dust, and planetoids. But in recent years, scientists have argued that this type of distribution may go beyond star systems and be intergalactic in scale. Some have even proposed intriguing new mechanisms for how this distribution could take place.
For instance, it is generally argued that meteorite and asteroid impacts are responsible for kicking up the material that would transport microbes to other planets. However, in a recent study, two Harvard astronomers examine the challenges that this would present and suggest another means – Earth-grazing objects that collect microbes from our atmosphere and then get flung into deep-space.
Continue reading “Comets and Interstellar Objects Could be Exporting Earth Life Out into the Milky Way”
Leave it up to the good ole Hubble Space Telescope. The workhorse telescope has given us a photo of the new interstellar comet 2I/Borisov. Take that, fancy new telescopes.
Continue reading “Here’s the Picture We’ve Been Waiting for. Hubble’s Photo of Interstellar Comet 2I/Borisov”
When the mysterious object known as ‘Oumuamua passed Earth in October of 2017, astronomers rejoiced. In addition to being the first interstellar object detected in our Solar System, but its arrival opened our eyes to how often such events take place. Since asteroids and comets are believed to be material left over from the formation of a planetary system, it also presented an opportunity to study extrasolar systems.
Unfortunately, ‘Oumuamua left our Solar System before any such studies could be conducted. Luckily, the detection of comet C/2019 Q4 (Borisov) this summer provided renewed opportunities to study material left by outgassing. Using data gathered by the William Herschel Telescope (WHT), an international team of astronomers found that 2I/Borisov contains cyanide. But as Douglas Adams would famously say, “Don’t Panic!”
Continue reading “Astronomers Find Cyanide Gas in Interstellar Object 2I/Borisov, but Don’t Panic Like it’s 1910”
It seems that comet 67P/Churyumov–Gerasimenko is not the stoic, unchanging Solar System traveller that it might seem to be. Scientists working through the vast warehouse of images from the Rosetta spacecraft have discovered there’s lots going on on 67P. Among the activity are collapsing cliffs and bouncing boulders.
Continue reading “Rosetta Saw Collapsing Cliffs and Other Changes on 67P During its Mission” | 0.8862 | 3.822802 |
Gas giants and icy moons
Despite their frigidity, the four planets past Mars (Jupiter, Saturn, Neptune,and Uranus) manage to produce some interesting weather. One of their moons even has an atmosphere surprisingly similar to Earth's. All four planets have been dubbed gas giants, because the bulk of their interiors are made up of gases rather than solids (though Neptune and Saturn also hold large amounts of ice). The makeup of these planets' atmospheres resembles the Sun more than earthly air: hydrogen predominates, followed by helium. Small amounts of methane, ammonia, sulphides and other ingredients help produce their wide variety of clouds and colours as seen from Earth.
Jupiter, the solar system's largest planet by far, features an ever-evolving array of clouds, as well as vivid lightning (observed by NASA) and spectacular aurorae. The clouds, which consist of ammonia and other compounds as well as water, change within an overall pattern long noted by astronomers: alternating bright and dark bands at varying latitudes. The bands reflect a more intricate version of a closer-to-home pattern. On Earth, air tends to rise and form clouds along the Equator and at roughly 60°N and S, while sinking air and dry conditions are common around 30°N and S and at the poles. These bands are a product of incoming sunlight and Earth's rotation. Jupiter spins far more rapidly – almost two and a half times faster than Earth – and it's encircled by more than a dozen alternating light and dark bands. NASA's Cassini spacecraft has spotted tiny, bright storms – too small to be visible from Earth – speckling the darker bands.
Since there's no solid surface to help brake Jupiter's circulation, its winds can scream at more than 600kph/380mph, often spinning around longlasting cyclones and anticyclones. The most famous is the Great Red Spot, which is bigger than Earth itself. It's the Methuselah of weather systems: first observed in the mid-1600s, the spot is still going strong. Though it's often referred to as a storm, the Great Red Spot is actually an anticyclone, which usually brings fair weather on Earth. The spot gets a continual supply of spin from its location, nestled between two of Jupiter's circulation bands and their alternating winds. Spacecraft have tracked other, smaller circulations across Jupiter, but none with the persistence and size of the Great Red Spot.
Saturn may have spectacular rings, but its visible weather features are more muted than Jupiter's. Its latitudinal bands are less vivid, and except near the poles, its winds typically blow from a constant direction (west), albeit at astounding speeds – sometimes topping 1600kph/1000mph. Like Jupiter, Saturn experiences water-based thunderstorms and lightning. Saturn's large-scale storm systems are generally shorter-lived than Jupiter's. A recurring feature called the Great White Spot sets in about every 30 years, roughly the amount of time Saturn takes to complete an orbit – but it only lasts for a few weeks at a time. The next appearance of the Great White Spot is expected in 2020.
Of the four outer planets, Uranus has the most humdrum weather. The atmospheric pots on both Jupiter and Saturn get stirred by the immense heat generated by their respective cores (both emit far more heat than they receive from the Sun). Uranus is much less dense, though, and with relatively little heat coming into its atmosphere from either its core or the Sun, there's isn't much action to observe. Perhaps the most distinctive thing about weather on Uranus is the incredibly slow transitions between light and dark, thanks to the planet's odd rotation. Unlike the other planets, which feature only slight season-producing tilts, Uranus lies nearly on its side, spinning around an axis just eight degrees off its orbital plane. Much like our own North and South Pole, this means that each year has just one sunrise and one sunset, in the case of Uranus, each separated by nearly 42 Earth years (since a Uranian year lasts about 84 of ours).
Neptune, in contrast, is a surprisingly lively place weatherwise. It boasts the strongest winds observed anywhere in the solar system, ripping along at speeds estimated to be as high as 2500kph/1600mph. The winds feed into massive, but surprisingly transient storms. In 1989 NASA's Voyager 2 discovered a cyclone the size of the Indian Ocean, quickly dubbed the Great Dark Spot. Five years later, the Hubble Space Telescope found that the Great Dark Spot was gone, with a similar storm now evident in the opposite hemisphere. Pluto hasn't got much of an atmosphere at all – its air is almost a million times less dense than Earth's. The biggest changes in Plutonian air are driven by the planet's markedly elliptical orbit. During its 248-year-long trip around the Sun, Pluto gets within 4.5 billion km/2.8 million miles of the Sun at its closest – closer even than Neptune – but it's more than 7.3 billion km/4.5 billion miles at its farthest. Some of the planet's icy coating evaporates as it nears the Sun and then freezes again during the more distant periods.
More than 100 moons have been found spinning around the four gas giants. Nearly all of these lack an atmosphere and thus are featureless weatherwise, though many are either composed largely of ice or coated with it (such as Europa, which orbits Jupiter and which may harbour liquid water below its ice-covered surface). Neptune's most famous moon, Triton, manages an ultra-thin atmosphere, fed by volcanoes that emit nitrogen and methane. A few other moons harbour a smattering of trace gases. But the only moon with a bona fide atmosphere is Saturn's Titan, which is actually larger than Mercury. Titan boasts a surface air pressure even higher than Earth's, and like our own atmosphere, that air consists mainly of nitrogen. Smaller amounts of methane and other hydrocarbons react in sunlight to produce an orange, smog-like haze that shrouds the surface in perpetual dusk. Occasionally methane and ethane drop from the Titanian sky in the form of rainstorms. Right now Titan is a dependably cold place – temperatures average around –180°C/–292°F – but some astronomers have speculated that it could serve as a potential platform for life in a few billion years, as the Sun expands and warms its atmosphere. | 0.872554 | 3.964541 |
The SETI Institute is following up on the possibility that the stellar system KIC 8462852 might be home to an advanced civilization.This star, slightly brighter than the Sun and more than 1400 light-years away, has been the subject of scrutiny by NASA’s Kepler space telescope. It has shown some surprising behavior that’s odd even by the generous standards of cosmic phenomena. KIC 8462852 occasionally dims by as much as 20 percent, suggesting that there is some material in orbit around this star that blocks its light.
For various reasons, it’s obvious that this material is not simply a planet. A favored suggestion is that it is debris from comets that have been drawn into relatively close orbit to the star.
But another, and obviously intriguing, possibility is that this star is home to a technologically sophisticated society that has constructed a phalanx of orbiting solar panels (a so-called Dyson swarm) that block light from the star.
To investigate this idea, we have been using the Allen Telescope Array to search for non-natural radio signals from the direction of KIC 8462852. This effort is looking for both narrow-band signals (similar to traditional SETI experiments) as well as somewhat broader transmissions that might be produced, for example, by powerful spacecraft.
But what if ET isn’t signaling at radio frequencies? Our ATA observations are being augmented by a search for brief but powerful laser pulses. These observations are being conducted by the Boquete Optical SETI Observatory in Panama, part of a nascent global network of optical SETI observatories.
Both the observations and the data analysis are now underway. Once the latter is concluded, we will, of course, make them known here and in the professional journals.
On the basis of historical precedent, it’s most likely that the the dimming of KIC 8462852 is due to natural causes. But in the search for extraterrestrial intelligence, any suggestive clues should, of course, be further investigated – and that is what the SETI Institute is now doing.
Dr. Seth Shostak, Senior Astronomer
53 Συνολο, 2 Σήμερα | 0.916178 | 3.774368 |
Slide21965 Mars 1979 Jupiter 1980 Satum Early Solar System 1986 Uranus 1990 Neptune
Slide3Pluton Once the ninth planet from the sun, Pluto is unlike other planets in many respects. It is smaller than Earth's moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune's path and once again became the solar system's most distant planet until it was demoted to dwarf planet status. Pluto’s orbit is tilted to the main plane of the solar system where the other planets orbit by 17.1 degrees. NASA's New Horizons mission performed history's first flyby of the Pluto system on July 14, 2015.
Slide4Neptune The eighth planet from the sun, Neptune is known for strong winds sometimes faster than the speed of sound. Neptune is far out and cold. The planet is more than 30 times as far from the sun as Earth. It has a rocky core. Neptune was the first planet to be predicted to exist by using math before it was detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth.
Slide5Uranus The seventh planet from the sun, Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt. The tilt causes extreme seasons that last 20- plus years, and the sun beats down on one pole or the other for 84 Earth-years. Uranus is about the same size as Neptune. Methane in the atmosphere gives Uranus its blue-green tint.
Slide6Saturn The sixth planet from the sun is known most for its rings. When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing a symbol with one large circle and two smaller ones in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings. The rings are made of ice and rock. The gaseous planet is mostly hydrogen and helium. It has numerous moons.
Slide7Jupiter The fifth planet from the sun, Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.
Slide8Mars The fourth planet from the sun is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And Mars harbors water ice. Scientists think it was once wet and warm, though today it’s cold and desert-like. Mars' atmosphere is too thin for liquid water to exist on the surface for any length of time. Scientists think ancient Mars would have had the conditions to support life.
Slide9Earth The third planet from the sun, Earth is a water world, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface rotates about its axis at 1,532 feet per second (467 meters per second) slightly more than 1,000 mph (1,600 kph) at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second).
Slide10Venus The second planet from the sun, Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth, Venus' thick, toxic atmosphere traps heat in a runaway "greenhouse effect." Oddly, Venus spins slowly in the opposite direction of most planets.
Slide11Mercury The closest planet to the sun, Mercury is only a bit larger than Earth's moon. Its day side is scorched by the sun and can reach 840 degrees Fahrenheit (450 Celsius), but on the night side, temperatures drop to hundreds of degrees below freezing. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon.
Slide12SUN Earth and the other three inner planets of our solar system (Mercury, Venus, and Mars) are made of rock, containing common minerals like feldspars and metals like magnesium and aluminum.
Slide17THANK YOU SOURCE : https://www.nationalgeographic.com/science/space/our-solar-system/, https://www.space.com/16080-solar- system-planets.html | 0.862696 | 3.488428 |
Hundreds of sunrise and sunset times reveal that there’s something amiss with our calculations.
Every 24 hours, most of us plunge into darkness. We ride the whizzbang merry-go-round of our planet as it turns, racing 1,675 kilometers per hour (1,041 mph) over the horizon and headlong into night. Lest we lose ourselves in the star-speckled blackness — or, as is increasingly true for so many, in the sickly blaze of artificial lights — this ride carries us around and into the dawn again with dependable regularity.
After millennia attuned to this cosmic clock, you would think we’d know precisely when the Sun rises and sets. But Michigan Tech dissertation work by Teresa Wilson (now at the U.S. Naval Observatory) suggests that our estimates are often off by 1 to 5 minutes.
Conventionally speaking, sunrise and sunset are defined as the moment when the top of the Sun’s disk is on the horizon. If we lived on an airless body, we could calculate when this moment happens with simple geometry and call it a day. But light doesn’t travel from our star to our eye in a straight line. Sunlight’s path bends slightly when it hits Earth’s atmosphere, an effect which strengthens as the light burrows deeper into the increasingly dense atmosphere. This bending effect is called refraction, and it’s strongest at the horizon.
All publicly available calculators that Wilson could find assume an angle of refraction at the horizon of 34 arcminutes (denoted ʹ), or a little more than the size of the full Moon. This value may have come from Isaac Newton in the 1600s; Wilson found it cited as a standard as early as 1865. But using a single refraction angle doesn’t account for different meteorological conditions from location to location — in essence, we’re saying things are the same in July in Hawai‘i as they are in January in Alaska, she said January 8th during her presentation at the winter American Astronomical Society meeting in Seattle. Nor does this approach take into account how the observer’s altitude might change things.
Wilson decided to find out just how good our sunrise and sunset estimates are. She scoured published and unpublished data for every record she could find, ultimately amassing 251 sunrises and 514 sunsets from 30 different geographic coordinates, over both water and land horizons. About 600 of these came with weather data, which she fed into three different refraction models of varying complexity; for the others, she had to settle for the 34ʹ.
She found that, overall, predicted times varied in accuracy by location and season, with sunrise times over land generally being early in the summer months and late in the winter. Summer showed the largest discrepancies, probably due to the pronounced refractive effect that the large temperature difference in the atmosphere has during those months. Mirage effects due to cold air topped by warm over water horizons also exacerbated lags in sunset times throughout the year, sometimes by up to 5 minutes. Accounting for the observer’s altitude above the horizon did notably improve predictions for water horizons, however.
Furthermore, the more complex refraction models that incorporated meteorological conditions didn’t do a better job: Their inherent, limited assumptions about the behavior of the weather layer in Earth’s atmosphere, called the troposphere, led to them congregating around the 34ʹ value. Regardless of model, she concluded, sunrise and sunset times can’t be reliably predicted to better than 2 minutes.
Two minutes might sound inconsequential, but Wilson noted that, if GPS fails, sailors will use celestial navigation. “Most sailors will tell you that they can get their position with celestial navigation to within 1 nautical mile,” she said. But if part of that calculation involves sunset, “1 minute of time turns into 15 nautical miles of error.” Knowing precise sunrise and sunset times could also benefit observers, both amateur and professional. A better understanding of how the atmosphere bends light on the horizon would affect moonrise predictions, too.
Wilson, Teresa. “Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting Sunrise and Sunset Times.” Abstract 225.02D. 233rd American Astronomical Society meeting. Presented January 8, 2019.
Wilson, Teresa, “Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting Sunrise and Sunset Times.” Open Access Dissertation, Michigan Technological University. 2018.
Want to see the Sun go dark? Watch our webinar to learn how to plan for a solar eclipse expedition. | 0.855563 | 3.855119 |
A pair of new studies claim to have discovered two of the most distant objects ever seen in the outer reaches of the Solar System, including a “Super Earth” located six times further away than Pluto. It’s an extraordinary claim — and it’s also highly unlikely.
Before we dive in, it’s important to point out that neither study has gone through peer review, though both papers have been submitted to Astronomy & Astrophysics. The studies have already received considerable attention, however, owing to their remarkable claims.
Research groups from Sweden and Mexico analysed data collected by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. They were looking at a distant star called W Aquilae (or W Aql), and the nearby star Alpha Centauri. Remarkably enough, the researchers were looking for objects outside our Solar System, but they ended up (potentially) discovering objects much closer to home.
Of Centaurs and Brown Dwarfs
In the W Aql study, the astronomers pinpointed a potential object in March 2014 and then again in April. They say it’s probably a single object — one located in the outer reaches of the Solar System.
“Until the nature of the source becomes clear, we have named it Gna,” write the authors in the study. “Unless there are yet unknown, but significant, issues with ALMA observations, we have detected a previously unknown objects [sic] in our solar system.”
The two ALMA detections on March 20 and April 14, 2014. (Credit: V. H. T. Vlemmings et al., 2015)
Estimates place the apparent object between 12 to 25 AU (where 1 AU = average distance of Earth to the Sun), with a size of about 220 to 880km. Such a conclusion would hardly be surprising as there are literally millions of icy objects at that distance. As Paul Gilster notes at Centauri Dreams, Gna is probably a Centaur in retrograde orbit — a Centaur being a minor planet at the edge of the Solar System, not unlike Pluto and its companion, Eris.
But these estimates only apply if it’s gravitationally bound. In the event that it’s “unbound”, the astronomers say it could be a “much larger, planet-sized object” located within 4000 AU (whoa!), or even beyond to about 0.3 parsecs, which is about 61,900 AU (even more whoa!). For comparison, Pluto is located 34 AU from Earth. So if this supposed object exists, it’s way the hell out there in the outer reaches of the Solar System.
“[The] most exciting possibility is that we have observed a planetary body or brown dwarf in the outer reaches of the Oort cloud,” write the authors. The presence of a brown dwarf — an object too big to be a true planet, but too small to be a star — would truly be a remarkable thing.
More observations will be required to confirm this one way or another; the astronomers are working with precious little data.
Observations of the “Alpha Cen” object, designated “U”. (Credit: R. Liseau et al., 2015)
Which now brings us to the second study, which is a equally as interesting, though a bit more controversial.
A different set of observations made by the same research team indicates the presence of an object that appears to share the same motion as Alpha Centauri A and B. But this probably isn’t another star in the Alpha Cen system because it’s far too bright. Rather, the authors conjecture that it’s one of three possible things: (1) a small, icy Trans Neptunian Object (TNO) at a distance of 100 AU, (2) a Super Earth located 300 AU away, or (3) a super-cool brown dwarf located at a distance of about 20,000 AU. Again, wow.
Neat, But Not Likely
Bad Astronomer Phil Plait says that an icy body at the distance of Neptune isn’t a big stretch, but as for the other possibilities, they’re “far less likely”. He says the discovery of such an object is grossly improbable, and asks us to think of it this way:
If they did find a planet looking at such a small piece of sky, it would imply that it’s likely the sky is full of such objects! That removes the coincidence; there are so many you were bound to find one.
But if true, that would mean there are hundreds of thousands of such objects in the solar system. More! That makes a planet-sized object pretty unlikely, to say the least. I might believe that it could be one of many smaller (several hundred km in diameter) chunks of ice way past Neptune because those are common. But even then it’s still unlikely given these circumstances.
Fun fact: if it is true that ALMA accidentally discovered a massive outer solar system object in its tiny tiny tiny field of view that would suggest that there are something like 200,000 Earth sized planets in the outer solar system. Which, um, no. Even better: I just realised that this many Earth-sized planets existing would destabilize the entire solar system and we would all die.
Jonathan McDowell, an astronomer with the Harvard-Smithsonian Center for Astrophysics, says it’s much too early to get excited.
“It’s a considerable stretch to make the claim of an outer solar system object at this stage,” he told Gizmodo. “Maybe there is a large faint population of variable obscured quasars that’s combining in some weird way with ALMA instrumental issues, or — who knows.”
McDowell suspects it may be a classic case of ‘we should have waited for the referees’ report before going on arXiv’.
Indeed, you can find both studies at the pre-print arXiv: “The serendipitous discovery of a possible new solar system object with ALMA” and “A new submm source within a few arcseconds of α Centauri: ALMA discovers the most distant object of the solar system.” Both papers have been submitted to Astronomy & Astrophysics for peer review. | 0.802094 | 3.921214 |
Small planetary systems with multiple planets are not fans of heavy metal — think iron, not Iron Maiden — according to a new Yale University study.
Researchers at Yale and the Flatiron Institute have discovered that compact, multiple-planet systems are more likely to form around stars that have lower amounts of heavy elements than our own Sun. This runs counter to a good deal of current research, which has focused on stars with higher metallicity.
The research team looked at 700 stars and their surrounding planets for the study, which appears in The Astrophysical Journal Letters. The researchers considered any element heavier than helium — including iron, silicon, magnesium, and carbon — as a heavy metal.
“We used iron as a proxy,” said lead author John Michael Brewer, a postdoctoral researcher at Yale who works with astronomy professor Debra Fischer. “These are all elements that make up the rocks in small, rocky planets.”
Brewer said an abundance of compact, multi-planet systems around low-metallicity stars suggests several things.
Credit: Illustration by Michael S. Helfenbein
First, he said, it may indicate that there are many more of these systems than previously assumed. Until recently, research instruments have not had the necessary precision to detect smaller planets and instead focused on detecting larger planets. Now, with the advent of technology such as the Extreme Precision Spectrometer (EXPRES) developed by Fischer’s team at Yale, researchers will be able to find smaller planets.
In addition, Brewer said, the new study suggests that small planetary systems may be the earliest type of planetary system, making them an ideal place to search for life on other planets. “Low-metallicity stars have been around a lot longer,” Brewer said. “That’s where we’ll find the first planets that formed.”
Fischer, who is a co-author of the study, demonstrated in 2005 that higher metallicity in stars increased the probability of forming large, Jupiter-like planets. This provided strong support to the core-accretion model for gas giant planet formation and established this as the leading mechanism for planet formation.
Understanding the formation of smaller planets has been more elusive.
“Our surprising result, that compact systems of multiple, small planets are more likely around lower metallicity stars suggests a new, important clue in understanding the most common type of planetary system in our galaxy,” said co-author Songhu Wang, a 51 Pegasi b Fellow at Yale.
Another tantalizing possibility to explore, according to the researchers, is the connection between iron and silicon in the birth of planets. The new study shows a high silicon-to-iron ratio in stars with lower metallicity.
“Silicon could be the secret ingredient,” Fischer said. “The ratio of silicon to iron is acting as a thermostat for planet formation. As the ratio increases, nature is dialing up the formation of small, rocky planets.”
The National Science Foundation helped support the research. Wang’s fellowship is supported by the Heising-Simons Foundation.
Contacts and sources:
Citation: Compact Multi-planet Systems are more Common around Metal-poor Hosts.
John M. Brewer, Songhu Wang, Debra A. Fischer, Daniel Foreman-Mackey. The Astrophysical Journal, 2018; 867 (1): L3 DOI: 10.3847/2041-8213/aae710 . | 0.853751 | 3.889292 |
From a great distance, our Milky Way would look like a thin disc of stars that rotates once every few hundred million years around its central region. Hundreds of billions of stars provide the gravitational glue to hold it all together.
But the pull of gravity is much weaker in the galaxy’s far outer disc. Out there, the hydrogen clouds that make up most of the Milky Way’s gas disc are no longer confined to a thin plane. Instead, they give the disc an S-like, warped appearance.
Although the Milky Way’s warped hydrogen gas layer had been known for decades, in research published today in Nature Astronomy, we discovered that a disc of young, massive stars there is warped too, and in a progressively twisted spiral pattern.
We were able to determine this twisted appearance after having developed the first accurate three-dimensional picture of the Milky Way’s stellar disc out to its far outer regions.
Mapping the Milky Way
Trying to determine the real shape of our galaxy is like standing in a Sydney garden and attempting to determine the shape of Australia. The Milky Way is all around us, so to determine its shape, we would need to map the distributions of stars in all directions.
While that is not particularly difficult in directions above and below the stellar disc plane, it becomes much harder along the Milky Way’s plane.
Other than stars and hydrogen gas clouds in the Milky Way’s plane, our view is obscured by huge quantities of dust. The material astronomers call dust is made up of carbon particles. It is not too different from the soot that builds up in your home if, for example, you have an open fire.
Large quantities of dust obscure our view of what lies beyond, but dust also makes light look redder. This is because the size of those carbon particles is close to the wavelength of blue light. Therefore, blue light can be absorbed quite easily by the dust while red light passes through without too much trouble.
But it’s not just the presence of dust that makes mapping our Milky Way galaxy troublesome. It is notoriously difficult to determine distances from the Sun to parts of the Milky Way’s outer disc without having a clear idea of what that disc actually looks like.
One of the researchers in my international team – Xiaodian Chen of the National Astronomical Observatories (Chinese Academy of Sciences) in Beijing – compiled a new catalogue of well-behaved variable stars known as classical Cepheids. These stars vary in brightness over a period of time.
These stars are among the best mileposts in astronomy: they can be used to determine very accurate distances with uncertainties of only 3-5%. This is pretty much as good as it gets in astronomy, allowing us to obtain the most accurate map of the outer Milky Way available to date.
Our new catalogue was based on observations made with NASA’s Wide-field Infrared Survey Explorer (WISE), a space telescope fitted with long-wavelength (infrared) glasses, ideal to look through any dust in the Milky Way’s disc.
The Cepheids mapped range from the Milky Way’s centre to its outer regions with most on the near side of the centre of our galaxy because of observational limitations.
Classical Cepheids are young stars that are some 4 to 20 times as massive as our Sun, and up to 100,000 times as bright. Such high stellar masses imply that these stars live fast and die young, burning through the hydrogen fuel in their stellar interiors very quickly, sometimes in only a few million years.
Cepheids show day- to month-long pulsations, which can be observed quite easily as changes in their brightness. Combined with a Cepheid’s observed average brightness, the period of its pulsation cycle can be used to obtain an accurate distance.
We all warp together
Somewhat to our surprise, we found that our collection of 1,339 Cepheid stars and the Milky Way’s gas disc follow each other closely. Until our recent study, it had not been possible to tie the distribution of young stars in the Milky Way’s outer disc so well to the flaring and warped disc made up of hydrogen gas clouds.
But perhaps more importantly, we discovered that the stellar disc is warped in a progressively twisted spiral pattern.
Many spiral galaxies are warped to varying extents, such as the galaxy ESO 510-G13 (pictured top) in the southern constellation Hydra, roughly 150 million light-years from Earth. However, only a dozen other galaxies were known to also show similarly twisted patterns in their outer discs.
Combining our results with these earlier observations, we concluded that the Milky Way’s warped and twisted spiral pattern is likely caused by forced torques from the galaxy’s massive inner disc. The rotating inner disc is, in essence, dragging the outer disc along, but since the outer disc’s rotation is lagging the resulting structure is a spiral pattern.
This new map provides a crucial update for studies of our galaxy’s stellar motions and the origins of the Milky Way’s disc. This is particularly interesting given the wealth of information we anticipate to receive from the European Space Agency’s Gaia satellite mission.
Gaia aims to eventually map our Milky Way in unprecedented detail, based on the most accurate distance determinations to the galaxy’s brightest stars ever obtained. | 0.837721 | 3.982575 |
Please use this identifier to cite or link to this item:
Imaging the water snow-line during a protostellar outburst
|Title:||Imaging the water snow-line during a protostellar outburst|
|Authors:||Cieza, Lucas A.|
Williams, Jonathan P.
show 11 morePerez, Sebastian
Dunham, Michael M.
Prieto, Jose L.
Principe, David A.
Schreiber, Matthias R.
|Date Issued:||14 Jul 2016|
|Abstract:||A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains^1, 2, 3, 4, 5, 6. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra^7, 8, 9 and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars^11). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation5, and the formation of comets, ice giants and the cores of gas giants^12. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate^13. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions^14: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation^15, 16, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.|
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Items in ScholarSpace are protected by copyright, with all rights reserved, unless otherwise indicated. | 0.835684 | 3.773143 |
The NASA Astrobiology Institute (NAI) and the Solar System Exploration Research Virtual Institute (SSERVI) will co-host a workshop next week at NASA’s Ames Research Center in California to discuss the potential for finding life in the watery plumes spraying up from Jupiter’s moon Europa. The plumes were discovered more than a year ago, and since then these potential windows to the moon’s subsurface have become a principal focus in the search for life beyond Earth.
Europa is thought to be covered by an ice crust several miles thick. In some spots, like the areas of so-called “chaotic terrain,” the crust is so cracked that water seems to be spouting out due to tidal stresses. Speculation began decades ago, when the Galileo spacecraft toured the Jovian system, that the subsurface ocean might be habitable. In fact, Europa may be the only body in the Solar System that has a chance of hosting life more complex than just microbes.
Scientists at the workshop, which is scheduled for February 18, will hone in on that possibility and the idea of analyzing water samples from the plume, searching for chemical clues as to whether the subsurface ocean is habitable or even contains microbial cells today. The first question is what measurements would be needed to detect and characterize life in an acquired water sample, and what instruments could take these measurements. Do the instruments exist already, or would they have to be developed? Other issues up for discussion are how the water samples could best be collected and whether they’d have to be specially prepared for analysis.
One possibility for sampling the plumes is to use cubesat(s) deployed from a larger Europa-bound spacecraft. The greatest challenge for any Europa mission, however, will be to withstand Jupiter’s extreme radiation field. Radiation would rapidly change the chemical (and biological, if any) content of a water sample, so collecting water from a Europan plume will be a tricky proposition.
The one-day meeting will be webcast live at https://ac.arc.nasa.gov/europa. | 0.820871 | 3.407586 |
If planets were products their price would be tumbling. Little more than a generation ago, we knew of only eight planets in all the universe—the ones within our own solar system. Only two of them, Earth and Mars, were plausibly capable of supporting life and only one of those definitely does. Planetary demand far exceeded supply.
Now, however, the market has been flooded. Thanks to advances in ground-and space-based observatories, especially the Kepler Space Telescope, which was launched in 2009 and operated for nine years, the population of known exoplanets — or planets orbiting other stars — has exploded to more than 4,000, with about another 4,000 detected but yet to be confirmed. Virtually every star in the universe is thought to be home to at least one planet, with some hosting an entire litter.
But a big sample group does not mean that science has yet discovered the true jackpot world: an Earth-like planet with a solid surface, an atmosphere and liquid water. If you’re looking for life, that’s where you’re likeliest to find it. Now, that jackpot—minus the life (so far)—appears to have been hit. According to a study by a team of researchers from the Center for Planetary Sciences at the University College London (UCL) and published today in Nature Astronomy, a potential garden planet, going by the prosaic name K2-18b, has been found just 110 light years from Earth.
“From today onwards, we know K2-18b has atmosphere and water, making it the best known candidate for habitability,” says Angelos Tsiaris, a UCL research associate in the Department of Physics and Astronomy and the lead author of the Nature paper.
Discovered in 2015, K2-18b was one more of the thousands of planets discovered by Kepler. The telescope did its work not by imaging its target planets directly, but rather by detecting the slight dip in light whenever the planet orbited in front of the Earth-facing side of its star. The frequency of the dip tells you how long each orbit takes and the amount of the dimming tells you the planet’s diameter—the bigger the world the more light is briefly lost.
Using those techniques, Kepler scientists determined that K2-18b is about twice the diameter of Earth and zips through its orbit once every 33 days. Two years later, European astronomers used a ground-based telescope to measure the amount of wobble K2-18b causes in its planet star as it orbits, which reveals the planet’s mass; the greater the wobble the more massive the world. Using those findings they concluded that K2-18b weighs in at about 8 times Earth’s mass.
That combination of diameter and mass put the planet in the category known as super-Earths — bigger than our comparatively small world; smaller than gas giants like Jupiter and Neptune; and likely to have a solid, rocky surface. In terms of life, that’s a good start. But K2-18b’s zippy orbit could also present problems. In order to complete a revolution so fast, the planet had to be situated very close to its sun—just 13 million miles away, the Kepler scientists calculated. Earth, by comparison, is 93 million miles from our sun. Mercury is just 36 million — giving it a surface temperature of 800º F (427º C).
Proximity is not a problem for K2-18b, however. Its sun is not a hot yellow star like ours, but a smaller, cooler red dwarf. That means its so-called habitable zone — the distance at which surface temperatures on the planet are within the narrow range to allow liquid water to exist — would be much closer. Correcting for the cooler fires of a red dwarf, astronomers conclude that even at so close a remove, K2-18b has surface temperatures that range from a low of -100º F (-73º C) to a high of 116º F (47º C).
Still, the question remained: Does the liquid water that could exist there actually exist there? To get the answer, the UCL team turned to one of the great workhorses of modern astronomy, the Hubble Space Telescope. Launched in 1990, Hubble predates the discovery of the very first exoplanet by two years, but its age is no bar to its ongoing productivity. The UCL researchers made use of the telescope’s Wide Field Camera 3, an instrument that can see in visible wavelengths, as well as in ultraviolet and near-infrared. What they were looking for were chemical signatures of K2-18b’s atmosphere—both whether the planet has an atmosphere at all, and whether that atmosphere contains water. They knew the work would be challenging.
“The measurements involved were extremely difficult,” says Tsiaris. “Like trying to identify one person in a crowd of ten thousand.”
But the precision of the Hubble and the tenacity of the researchers were up to the task, and over the course of multiple observations, they concluded that not only does the planet have water, it seems to have lots of it—making up as much as 50 percent of the atmosphere. It took a long time, however, before they were confident enough in their findings to announce them to the world.
“I had the results a year ago,” Tsiaris says. “At first we weren’t sure exactly what it meant, but we knew we had something exciting. It took us a year of repeating data analyses to make sure that what we say we found was correct. To get you to these two facts—there is atmosphere and there is water—took a lot of effort.”
K2-18b will surely be receiving more attention from astronomers around the world, not only with existing telescopes but with next-generation ones, including NASA’s James Webb Space Telescope, tentatively set for launch in 2021; and the European Space Agency’s ARIEL space telescope, specifically designed to study the atmosphere of exoplanets, and targeted for a 2028 launch. Already though, the K2-18b findings are encouraging more investigations of potentially similar worlds.
“If planets like Earth are very common,” says Tsiaris, “we can say life is very common.” That, of course, is an assumption that has yet to be proven, but with today’s announcement, the proof is closer than it’s ever been. —With reporting by Maddy Roache/London | 0.894387 | 3.867439 |
Look back far enough in time (and hence far enough in distance) and you see things that don’t correspond to nearby cosmic objects. The so-called ‘Lyman-alpha blobs’ that astronomers have found associated with young, distant galaxies are a case in point. Huge collections of hydrogen gas (some of them the largest single objects yet found in the universe), they’re bright at optical wavelengths, raising the question of what powers the glow and how they factored into the galaxy formation process.
New research may be offering an answer. The key is something called ‘feedback,’ a stage in galaxy formation that shows the interplay between galaxies and the intergalactic medium. Here, the cooling of gas within the dark matter halos enshrouding a young galaxy is countered by heating from active galactic nuclei (think supermassive black holes), which helps to enrich intergalactic space and also slow down star formation.
Image: An artist’s representation showing what one of the galaxies inside a blob might look like if viewed at a relatively close distance. The spiral arms of the galaxy are seen in yellow and white. A two-sided outflow powered by the supermassive black hole buried inside the middle of the galaxy is shown in bright yellow, above and below the galaxy. This outflow illuminates and heats gas surrounding the galaxy, enabling this blob to be seen across billions of light years. Credit: CXC/M. Weiss.
The instrument at work here is the Chandra X-ray Observatory, which has pinpointed the effects of supermassive black holes that, even as they grow, are obscured by the dense layers of gas and dust around them. Also implicated as a power source is the contribution of intense star formation found in these regions. The Lyman-alpha blobs found in an area of sky known as SSA22 are produced by galaxies that are ending their era of rapid growth, and now offer us an insight into how galaxies form.
Bret Lehmer (Durham University, UK), a co-author of the paper on this work, explains the process:
“We’re seeing signs that the galaxies and black holes inside these blobs are coming of age and are now pushing back on the infalling gas to prevent further growth. Massive galaxies must go through a stage like this or they would form too many stars and so end up ridiculously large by the present day.”
Thus the radiation and outflows from black holes and bursts of star formation are powerful enough to illuminate the hydrogen gas of the blobs in which they reside. That’s no small feat, considering that these blobs of gas are several hundred thousand light years across. We’re looking at them at a time when the universe was roughly two billion years old. Rather than galaxies in their infancy, we are evidently seeing galaxy formation as it begins to move away from the period of early rapid growth.
Galaxies in their adolescence? SSA22 offers powerful evidence for that belief. That points to a future where, rather than forming stars, the gaseous blobs will contribute to the gas found between the galaxies. This striking stage of galaxy formation, so unlike the mature galaxies we see in later eras, offers clues to the still earlier era when the flow of gas is inwards and the infant galaxy cools as it emits radiation.
The paper is Geach et al., “The Chandra Deep Protocluster Survey: Ly-alpha Blobs are powered by heating, not cooling,” accepted by the Astrophysical Journal and available online. A Chandra X-ray Observatory news release is also available. | 0.801476 | 4.138929 |
Given that our Solar System sits inside the Milky Way Galaxy, getting a clear picture of what it looks like as a whole can be quite tricky. In fact, it was not until 1852 that astronomer Stephen Alexander first postulated that the galaxy was spiral in shape. And since that time, numerous discoveries have come along that have altered how we picture it.
For decades astronomers have thought the Milky Way consists of four arms — made up of stars and clouds of star-forming gas — that extend outwards in a spiral fashion. Then in 2008, data from the Spitzer Space Telescope seemed to indicate that our Milky Way has just two arms, but a larger central bar. But now, according to a team of astronomers from China, one of our galaxy’s arms may stretch farther than previously thought, reaching all the way around the galaxy.
This arm is known as Scutum–Centaurus, which emanates from one end of the Milky Way bar, passes between us and Galactic Center, and extends to the other side of the galaxy. For many decades, it was believed that was where this arm terminated.
However, back in 2011, astronomers Thomas Dame and Patrick Thaddeus from the Harvard–Smithsonian Center for Astrophysics spotted what appeared to be an extension of this arm on the other side of the galaxy.
But according to astronomer Yan Sun and colleagues from the Purple Mountain Observatory in Nanjing, China, the Scutum–Centaurus Arm may extend even farther than that. Using a novel approach to study gas clouds located between 46,000 to 67,000 light-years beyond the center of our galaxy, they detected 48 new clouds of interstellar gas, as well as 24 previously-observed ones.
For the sake of their study, Sun and his colleagues relied on radio telescope data provided by the Milky Way Imaging Scroll Painting project, which scans interstellar dust clouds for radio waves emitted by carbon monoxide gas. Next to hydrogen, this gas is the most abundant element to be found in interstellar space – but is easier for radio telescopes to detect.
Combining this information with data obtained by the Canadian Galactic Plane Survey (which looks for hydrogen gas), they concluded that these 72 clouds line up along a spiral-arm segment that is 30,000 light-years in length. What’s more, they claim in their report that: “The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus (2011) as well as the Scutum-Centaurus Arm into the outer second quadrant.”
This would mean the arm is not only the single largest in our galaxy, but is also the only one to effectively reach 360° around the Milky Way. Such a find would be unprecedented given the fact that nothing of the sort has been observed with other spiral galaxies in our local universe.
Thomas Dame, one of the astronomers who discovered the possible extension of the Scutum-Centaurus Arm in 2011, was quoted by Scientific American as saying: “It’s rare. I bet that you would have to look through dozens of face-on spiral galaxy images to find one where you could convince yourself you could track one arm 360 degrees around.”
Naturally, the prospect presents some problems. For one, there is an apparent gap between the segment that Dame and Thaddeus discovered in 2011 and the start of the one discovered by the Chinese team – a 40,000 light-year gap to be exact. This could mean that the clouds that Sun and his colleagues discovered may not be part of the Scutum-Centaurus Arm after all, but an entirely new spiral-arm segment.
If this is true, than it would mean that our Galaxy has several “outer” arm segments. On the other hand, additional research may close that gap (so to speak) and prove that the Milky Way is as beautiful when seen afar as any of the spirals we often observe from the comfort of our own Solar System. | 0.857414 | 4.007702 |
Astronomers have found two objects that, added to a strange object discovered in 2018, constitute a new class of cosmic explosions. They share some characteristics with supernova explosions and gamma-ray bursts.
Scientists using the Hubble Space Telescope have detected quasars sending outbursts of energy roaring through their galaxies, according to new research.
This star is going to go nova (not supernova) by 2083. V Sagittae is in the constellation Sagitta and is s about 1100 light years from Earth. When the brightening happen, it will be historic. V Sge will appear startlingly bright in the night sky.
A titanic, expanding beam of energy sprang from close to the supermassive black hole in the center of the Milky Way just 3.5 million years ago, sending a cone-shaped burst of radiation through both poles of the galaxy and out into deep space.
With globe-spanning collaboration that enables to alert various telescopes to train their sights on the event, we are getting closer and closer to understanding how massive stars end their life and what leads up to the final explosion.
A mysterious flash of X-rays has been discovered by NASA’s Chandra X-ray Observatory in the deepest X-ray image ever obtained. This source likely comes from some sort of destructive event, but may be of a variety that scientists have never seen before.
In 2009 astronomers detected an unusual object, named CX330, as a source of X-rays as it was surveying the center of the Milky Way galaxy but they had not idea what it was. Today, astronomers have a better idea to what this strange object is.
Astronomers have discovered a new cosmic explosion: a gamma-ray burst and its associated supernova. Gamma-ray bursts (GRBs) are the most powerful blasts in the Universe, and are thought to be created in the deaths of the most massive stars. | 0.915408 | 3.595518 |
This incredible image was captured ten years ago today, on January 14, 2005. It shows the murky surface of Saturn’s moon Titan as seen by the European Space Agency’s Huygens probe after it made its historic descent through the moon’s thick haze and clouds and landed in a frozen plain of crusty methane mud and icy pebbles. During the descent and after landing Huygens returned data for several hours before communication was lost. The groundbreaking images and information it sent back has proved invaluable to scientists studying this unique and mysterious moon, which is at the same time extremely alien and surprisingly Earth-like.
“It was eerie…we saw bright hills above a dark plain, a weird combination of light and dark. It was like seeing a landscape out of Dante.”
– Jonathan Lunine, Cassini-Huygens mission scientist
Learn more about the Huygens landing here and check out an incredible video below zooming in a billion times from Saturn orbit to Titan’s surface:
At first, the Huygens camera just saw fog over the distant surface. The fog started to clear only at about 60 kilometers (37 miles) altitude, making it possible to resolve surface features as large as 100 meters (328 feet). Only after landing could the probe’s camera resolve the little grains of sand. (NASA/JPL)
“Was I really living through all this? I distinctly recall the dreamy feeling of being in one universe one moment and in another universe the next. But it was no dream. We had, without doubt, journeyed to Titan, ten times farther from the Sun than the Earth, and touched it. The solar system suddenly seemed a very much smaller place.”
– Carolyn Porco, Cassini Imaging Team Leader and CICLOPS director
Learn more about some of the top ten discoveries of the Huygens probe here, and here’s an infographic of the numbers associated with Titan:
See more images and videos about Huygens’ historic landing at the CICLOPS site here. | 0.855165 | 3.081282 |
Following up on our recent discussion of interstellar distances and how they are determined comes word of a reassessment of the distance to the Orion Nebula. The star forming region is famous not only for its beauty but for the opportunity it gives us to assess young stars as they emerge from the interstellar gases around them. Their distance tells us something about their intrinsic brightness and thus their ages.
The change in distance revealed in the new studies is considerable. Whereas the previous best estimate to the Nebula was 1565 light years, the new one, drawn with an uncertainty of six percent, is 1270 light years, a twenty percent adjustment. The Very Long Baseline Array was behind this work, using familiar parallax methods to observe a star called GMR A from opposite sides of Earth’s orbit.
“This measurement is four times more precise than previous distance estimates,” says Geoff Bower (UC-Berkeley). “Because our measurement reduces the distance to this region, it tells us that the stars there are less bright than thought before, and changes the estimates of their ages.”
And what a change. These stars are twice as old as once thought.
What we’re still doing — and we’re early in the process — is getting an approximation of the three-dimensional structure of nearby interstellar space. VLBA is ideal for this work because its ten 25-meter radiotelescope dishes stretch from the Pacific (Hawaii) to the Caribbean (Virgin Islands), allowing it to produce images of remarkably high resolution. Huge amounts of work remain to be done as we adjust distances to various targets. It’s amazing to consider that if we somehow found a way to reach the stars tomorrow, we’d still be faced with the same conundrum experienced by sailors in the 16th Century, the absence of reliable maps.
VLBA has also made observations of star-forming regions in Taurus and Ophiuchus as well as examinations of the Milky Way’s spiral arms and pulsars. With operations managed from Socorro, New Mexico, it’s the world’s largest dedicated, full-time astronomical instrument. The new findings appear as Sandstrom et al., “A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations,” accepted by The Astrophysical Journal (abstract). | 0.810986 | 3.873573 |
A fleet of solar-sailing sentries stationed far from the sun could someday allow scientists to get up-close looks at interstellar visitors like the mysterious 'Oumuamua.
The NASA Innovative Advanced Concepts (NIAC) Program has funded a team of researchers to study the feasibility of building and deploying "statites" (short for "static satellites") at various points along the outer reaches of our solar system.
These lightsail-equipped spacecraft would use solar radiation pressure — the push from photons streaming from the sun — to "hover" in the same spot over time, keeping an eye out for interstellar objects (ISOs) zooming through their particular patch of space.
"Once an ISO is detected, the system can deliver a cubesat on either a flyby trajectory or on a rendezvous trajectory (with propulsion)," the research team, led by Richard Linares, an assistant professor in the Department of Aeronautics and Astronautics at the Massachusetts Institute of Technology (MIT), wrote in a description of the project. (A cubesat on the propulsion-free flyby option would rely solely on the sun's gravitational pull to direct it toward the ISO.)
This novel strategy might be the best way to get up-close looks at ISOs, team members said.
"There are a lot of fundamental challenges with observing ISOs from Earth — they are usually so small that light from the sun needs to illuminate it in a certain way for our telescopes to even detect it," Linares said in a statement.
"And they are traveling so fast that it’s hard to pull together and launch a mission from Earth in the small window of opportunity we have before it’s gone," he added. "We'd have to get there fast, and current propulsion technologies are a limiting factor."
Astronomers have spotted two confirmed ISOs to date. The first was 'Oumuamua, which zoomed through the inner solar system in the fall of 2017 and remains a bit of a puzzle to this day. The object's strange combination of characteristics — its weirdly elongated shape and curious nongravitational acceleration, for example — inspired some speculation that it might be an alien spacecraft of some sort.
The second, Comet Borisov, was first observed in August 2019. Borisov is less mysterious than 'Oumuamua, more obviously resembling the comets of our own solar system.
And scientists are sure to find more interlopers in the future, especially after the Vera C. Rubin Observatory gets up and running in Chile in the next year or so. Vera C. Rubin will survey large patches of sky repeatedly and in great detail, catching many "transients" such as ISOs, researchers have said.
These visitors are scientific gold mines waiting to be tapped, said statite project team member Benjamin Weiss.
"Studying an interstellar body close-up would revolutionize our understanding of planet formation and evolution," Weiss, a professor of planetary sciences at MIT, said in the same statement.
"For the first time, we could obtain sensitive measurements of the bulk composition of other solar systems," Weiss added. "We could also learn how quickly and how commonly objects transit between solar systems, which will tell us the feasibility of the interstellar transfer of life."
A statite launch is not imminent, however; Linares and his team received a NIAC Phase 1 award, which funds nine months of initial feasibility studies and idea development. The researchers could potentially advance their concept further via Phase 2 and Phase 3 NIAC funding, should they apply for and receive it.
- Why was 'Oumuamua so weird? New research tries to track its origins.
- 'Oumuamua and Borisov are just the beginning of an interstellar object bonanza
- Interstellar comet: Here's why it's got scientists so pumped up
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. | 0.88867 | 3.821503 |
When it comes to the future of space exploration, one of the greatest challenges is coming up with engines that can maximize performance while also ensuring fuel efficiency. This will not only reduce the cost of individual missions, it will ensure that robotic spacecraft (and even crewed spacecraft) can operate for extended periods of time in space without having to refuel.
In recent years, this challenge has led to some truly innovative concepts, one of which was recently build and tested for the very first time by an ESA team. This engine concept consists of an electric thruster that is capable of “scooping” scarce air molecules from the tops of atmospheres and using them as propellant. This development will open the way for all kinds of satellites that can operate in very low orbits around planets for years at a time.
The concept of an air-breathing thruster (aka. Ram-Electric Propulsion) is relatively simple. In short, the engine works on the same principles as a ramscoop (where interstellar hydrogen is collected to provide fuel) and an ion engine – where collected particles are charged and ejected. Such an engine would do away with onboard propellant by taking in atmospheric molecules as it passed through the top of a planet’s atmosphere.
The concept was the subject of a study titled “RAM Electric Propulsion for Low Earth Orbit Operation: An ESA Study“, which was presented at the 30th International Electric Propulsion Conference in 2007. The study emphasized how “Low Earth orbit satellites are subject to atmospheric drag and thus their lifetimes are limited with current propulsion technologies by the amount of propellant they can carry to compensate for it.”
The study’s authors also indicated how satellites using high specific impulse electric propulsion would be capable of compensating for drag during low altitude operation for an extended period of time. But as they conclude, such a mission would also be limited to the amount of fuel it could carry. This was certainly the case for the ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) gravity-mapper satellite,
While GOCE remained in orbit of Earth for more than four years and operated at altitudes as low as 250 km (155 mi), its mission ended the moment it exhausted its 40 kg (88 lbs) supply of xenon as propellant. As such, the concept of an electric propulsion system that an utilize atmospheric molecules as propellant has also been investigated. As Dr. Louis Walpot of the ESA explained in an ESA press release:
“This project began with a novel design to scoop up air molecules as propellant from the top of Earth’s atmosphere at around 200 km altitude with a typical speed of 7.8 km/s.”
To develop this concept, the Italian aerospace company Sitael and the Polish aerospace company QuinteScience teamed up to create a novel intake and thruster design. Whereas QuinteScience built an intake that would collect and compress incoming atmospheric particles, Sitael developed a dual-stage thruster that would charge and accelerate these particles to generate thrust.
The team then ran computer simulations to see how particles would behave across a range of intake options. But in the end, they chose to conduct a practice test to see if the combined intake and thruster would work together or not. To do this, the team tested it in a vacuum chamber at one of Sitael’s test facilities. The chamber simulated an environment at 200 km altitude while a “particle flow generator” provided the oncoming high-speed molecules.
To provide a more complete test and make sure the thruster would function in a low-pressure environment, the team began by igniting it with xenon-propellant. As Dr. Walpot explained:
“Instead of simply measuring the resulting density at the collector to check the intake design, we decided to attach an electric thruster. In this way, we proved that we could indeed collect and compress the air molecules to a level where thruster ignition could take place, and measure the actual thrust. At first we checked our thruster could be ignited repeatedly with xenon gathered from the particle beam generator.”
As a next step, the team partially replace xenon with a nitrogen-oxygen air mixture to simulate Earth’s upper atmosphere. As hoped, the engine kept firing, and the only thing that changed was the color of the thrust.
“When the xenon-based blue color of the engine plume changed to purple, we knew we’d succeeded,” said Dr. Walpot. “The system was finally ignited repeatedly solely with atmospheric propellant to prove the concept’s feasibility. This result means air-breathing electric propulsion is no longer simply a theory but a tangible, working concept, ready to be developed, to serve one day as the basis of a new class of missions.”
The development of air-breathing electric thrusters could allow for an entirely new class of satellite that could operate with the fringes of Mars’, Titan’s and other bodies atmospheres for years at a time. With this kind of operational lifespan, these satellites could gather volumes of data on these bodies’ meteorological conditions, seasonal changes, and the history of their climates.
Such satellites would also be very useful when it comes to observing Earth. Since they would be able to operate at lower altitudes than previous missions, and would not be limited by the amount of propellant they could carry, satellites equipped with air-breathing thrusters could operate for extended periods of time. As a result, they could offer more in-depth analyses on Climate Change, and monitor meteorological patterns, geological changes, and natural disasters more closely.
Further Reading: ESA | 0.804579 | 3.67901 |
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