Blue astronomy is focused on the wavelength range 450–475 nm. This may involve emission, absorption, transmission, and reflection. Stars are often referred to by their predominant color. For example, blue stragglers are found among the galactic halo globular clusters. Blue main sequence stars, that are metal poor, ([Fe/H] ≤ -1.0) are most likely not analogous to blue stragglers. "[G]round-based UV [and blue astronomy] is a powerful facility for [the] study of [the] chemical evolution of [the] early Galaxy." The UV and B astronomy are over the wavelength range 355.0–500.0 nm. Also, a topic of blue astronomy is the blueshift change in wavelength. When any effort to acquire a system of laws or knowledge focusing on an astr, aster, or astro, that is, any natural body in the sky especially at night, discovers an entity emitting, absorbing, transmitting, reflecting, or fluorescing blue, succeeds even in its smallest measurement, blue astronomy is the name of the effort and the result. Once an entity, source, or object has been detected as emitting, absorbing, transmitting, reflecting, or fluorescing blue, it may be necessary to determine what the mechanism is. Usually this information provides understanding of the same entity, source, or object. Blue is a color that suggests the sense of sight. Most people associate astronomy with the sense of seeing, what can be termed visual astronomy. As telescope optics transmit blue well, blue astronomy is also a field within optical astronomy. Def. of the higher-frequency region of the part of the electromagnetic spectrum which is relevant in the specific observation is called blue. Def. the colour of the clear sky or the deep sea, between green and violet in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this is called blue. The Earth's shadow or Earth shadow (also sometimes known as the dark segment) are names for the shadow that the Earth itself casts on its atmosphere. This shadow is often visible from the surface of the Earth, as a dark band in the sky near the horizon. This atmospheric phenomenon can sometimes be seen twice a day, around the times of sunset and sunrise. The effect of the Earth's shadow on the atmosphere is quite often visible in the sky, and yet often goes unrecognized. This shadow is visible to observers as it falls on the atmosphere of the Earth during the twilight hours. When the weather conditions and the observer's viewing point permit a clear sight of the horizon, the shadow can be seen as a dark blue or greyish-blue band. Assuming the sky is clear, the Earth's shadow is visible in the opposite half of the sky to the sunset or sunrise, and is seen right above the horizon as a dark blue band. In the image at right, the Earth's shadow at sunrise is seen over a horizon where the sea meets the sky, looking west from Twin Peaks, San Francisco. The lowest blue-grey area is not the sky but the surface of the Pacific Ocean. At left is the Earth's shadow at sunset, looking east from the Marin Headlands just north of San Francisco. There is a thin greyish cloud layer partially obscuring the horizon in this image. The Earth's shadow (as it is cast onto the atmosphere) can be observed during the twilight hours, assuming the sky is clear and the horizon is relatively unobstructed. At sunset the Earth's shadow is visible opposite the sunset in the eastern sky, just above the horizon. The shadow shows as a dark blue band that stretches over 180° of the horizon. It is most noticeable at the antisolar point, exactly opposite the sunset. "At sunrise, the Earth's shadow is seen in a similar way, but in the western sky. The Earth's shadow is best observed when there is a low horizon (such as over the sea), and when the sky conditions are very clear. In addition, the higher up an observer is standing to view the horizon, the sharper the shadow appears. At sunrise, the Earth's shadow can be seen to set as the sun itself rises, and at sunset, the Earth's shadow rises as the sun sets. "A solar tracker is a device that orients a payload toward the sun. Sunlight has two components, the "direct beam" that carries about 90% of the solar energy, and the "diffuse sunlight" that carries the remainder - the diffuse portion is the blue sky on a clear day and increases proportionately on cloudy days. As the majority of the energy is in the direct beam, maximizing collection requires the sun to be visible to the panels as long as possible. "Diffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. It is also called skylight, diffuse skylight, or sky radiation and is the reason for changes in the colour of the sky. Of the total light removed from the direct solar beam by scattering in the atmosphere (approximately 25% of the incident radiation when the sun is high in the sky, depending on the amount of dust and haze in the atmosphere), about two-thirds ultimately reaches the earth as diffuse sky radiation. "[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon". Blue is the colour of the clear sky and the deep sea. "De la couleur du ciel sans nuages, de l'azur" Often a mineral appears blue due to the presence of copper or sulfur. Glaucophane is a blue silicate that owes its color to its characteristic formation. Sodalite is a rich royal blue mineral massive sodalite samples are opaque, crystals are usually transparent to translucent. Occurring typically in massive form, sodalite is found as vein fillings in plutonic igneous rocks such as nepheline syenites. Covellite has been found in veins at depths of 1,150 meters, as the primary mineral. Covellite formed as clusters in these veins reaching one meter across. Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]. The colour is due to the presence of S3- anions. Lazurite is a product of contact metamorphism of limestone. A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram at right). Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in geological history of the area. The boundaries between facies (and corresponding areas on the temperature v. pressure graph), are wide, because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure, is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis. Blueschist is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius. The blue color of the rock comes from the presence of the mineral glaucophane. Blueschists are typically found within orogenic belts as terranes of lithology in faulted contact with greenschist or rarely eclogite facies rocks. ... Blueschist, as a rock type, is defined by the presence of the minerals glaucophane + ( lawsonite or epidote ) +/- jadeite +/- albite or chlorite +/- garnet +/- muscovite in a rock of roughly basaltic composition. Blueschist often has a lepidoblastic, nematoblastic or schistose rock microstructure defined primarily by chlorite, phengitic white mica, glaucophane, and other minerals with an elongate or platy shape. Grain size is rarely coarse, as mineral growth is retarded by the swiftness of the rock's metamorphic trajectory and perhaps more importantly, the low temperatures of metamorphism and in many cases the anhydrous state of the basalts. However, coarse varieties do occur. Blueschists may appear blue, black, gray, or blue-green in outcrop. Glaucophane is a mineral belonging to the amphibole group, chemical formula Na2Mg3Al2Si8O22(OH)2. The blue color is very diagnostic for this species. It, along with the closely related mineral riebeckite are the only common amphibole minerals that are typically blue. Glaucophane forms in metamorphic rocks that are either particularly rich in sodium or that have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone. This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. It is glaucophane's color that gives the blueschist facies its name. Glaucophane is also found in eclogites that have undergone retrograde metamorphism. Hauyne, haüyne or hauynite [occurs] in Vesuvian lavas in Monte Somma, Italy, ... It is a tectosilicate mineral with sulfate, with endmember formula Na3Ca(Si3Al3)O12(SO4). ... Haüyne occurs in phonolites and related leucite- or nepheline-rich, silica-poor, igneous rocks; less commonly in nepheline-free extrusives and metamorphic rocks (marble). Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of a glacier blue ice was observed in Tasman Glacier, New Zealand in January 2011. "Geologic evidence suggests that large amounts of water have likely flowed on Earth for the past 3.8 billion years—most of its existence. [It is] [b]elieved to have initially arrived on the surface through the emissions of ancient volcanoes". In Egypt, blue was associated with the sky and with divinity. The Egyptian god Amun could make his skin blue so that he could fly, invisible, across the sky. Blue could also protect against evil; many people around the Mediterranean still wear a blue amulet, representing the eye of God, to protect them from misfortune. Many of the gods in Hinduism are depicted as having blue-coloured skin, particularly those associated with Vishnu, who is said to be the Preserver of the world and thus intimately connected to water. Krishna and Ram, Vishnu's avatars, are usually blue. Shiva, the Destroyer, is also depicted in light blue tones and is called neela kantha, or blue-throated, for having swallowed poison in an attempt to turn the tide of a battle between the gods and demons in the gods' favour. Huitzilopochtli [at second right] was the patron god of the Mexica tribe. Originally he was of little importance to the Nahuas, but after the rise of the Aztecs, Tlacaelel reformed their religion and put Huitzilopochtli at the same level as Quetzalcoatl, Tlaloc, and Tezcatlipoca, making him a solar god. Over the South presides the Blue Tezcatlipoca, Huitzilopochtli, the god of war. Rama imaged at left is the Daśāvatāra seventh avatar of the god Vishnu in Hinduism, and a king of Ayodhya in Hindu scriptures. In a few Rama-centric sects, Rama is considered the Supreme Being, rather than an avatar. Rama was born in Suryavansha (Ikshvaku Vansham) later known as Raghuvansha after king Raghu. When depicted with his brother Lakshman and consort Sita, with Hanuman kneeling in a state of prayer, this form is called Ram Parivar, and is the typical fixture depicting Rama in Hindu mandirs, or temples. The Hindi word parivar translates as "family." The image above shows a blue glow in the surrounding air from emitted cyclotron particulate radiation. The image at right shows the blue light, towards the lower right, due to synchrotron radiation, of the jet emerging from the bright active galactic nucleus (AGN) core of Messier 87. At left is an image that shows the blue glow resulting from a beam of relativistic electrons as they slow down. This deceleration produces synchrotron light out of the beam line of the National Synchrotron Light Source. The Edinburgh-Cape Blue Object Survey is an astronomical catalog included in the list of astronomical catalogues. These catalogs are lists or tabulations of astronomical objects. They are grouped together because they share a common type, morphology, origin, means of detection, or method of discovery. "[T]he diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light." A synchrotron model for the continuum spectrum of the Crab Nebula fits the radiation given off. "The light blue background is the dayglow emission (less than 1 kR) caused by the interaction between the photoelectrons generated by solar UV radiation and atmospheric molecules and atoms." This background occurs when imaging an Earth aurora from space using ultraviolet astronomy at the VUV wavelengths (135.6 ± 1.5 nm and 149.3 ± 1.5 nm). "Isophotes of [blue (395.0-485.0 nm)] background starlight brightness (integrated starlight, diffuse galactic light, cosmic light) have been constructed near the celestial [NCP and SCP], ecliptic [NEP and SEP], and galactic [NGP and SGP] poles from observations accumulated by the Pioneer 10 [and 11] imaging photopolarimeter from beyond the asteroid belt." "Diffuse galactic [blue] light refers to starlight scattered by interstellar grains. Integrated light from extragalactic sources is referred to as cosmic light." "Earth-based observers are limited in their perception of background starlight, due to the presence of airglow line and continuum emission, zodiacal light, and the effects of atmospheric extinction and scattering." Some of the blue background data were collected on September 30, 1973 (day/year 279/73). "To determine the brightnesses, isophotes were generated from six days of merged data, chosen to optimize sky coverage. The days used and their heliocentric distances in AU are: 354/72 (3.27), 149/73 (4.23), 237/73 (4.64), 279/73 (4.81), 21/74 (5.08), 68/74 (5.15)." Conversion of units over the Pioneer blue (B) bandpass is 1 S 10 ( V ) B = 1.16 x 10 − 8 e r g c m − 2 s − 1 s r − 1 n m − 1 . {\displaystyle 1S_{10}(V)_{B}=1.16x10^{-8}ergcm^{-2}s^{-1}sr^{-1}nm^{-1}.} For example, NCP S 10 ( V ) B = 56 , {\displaystyle S_{10}(V)_{B}=56,} NEP S 10 ( V ) B = 66 , {\displaystyle S_{10}(V)_{B}=66,} and NGP S 10 ( V ) B = 31. {\displaystyle S_{10}(V)_{B}=31.} Whereas, SCP S 10 ( V ) B = 74 , {\displaystyle S_{10}(V)_{B}=74,} SEP S 10 ( V ) B = 128 , {\displaystyle S_{10}(V)_{B}=128,} and SGP S 10 ( V ) B = 26. {\displaystyle S_{10}(V)_{B}=26.} "Extreme flocculent galaxies (e.g., NGC 7793) have very little structure in their old stellar population disks. Most of the structure seen in blue [B passband, λeff ≈ 436.0 nm, using baked 103a-O emulsions behind GG 385 filters] phtographs of these galaxies is from star formation or from very weak stellar density ripples. ... Intermediate-type spiral galaxies (e.g. M33, M101) can have both prominent blue star-formation features ans strong stellar density arms at the same time. ... In the grand design and intermediate-type galaxies, the blueness of the arms is independent of the arm amplitude, indicating either that the rate of star formation saturates to a constant value in a stellar density wave or material arm, or that star formation is independent of these density variations." Of some 670 Perseids examined for colors from 1985, 1988, and 1989, 128 were blue meteors, 3 were multi-colored yellow-blue and one was blue-green [cyan]. The average pre-atmospheric velocity is 59.9 km/s. The Perseids are a prolific meteor shower associated with the comet Swift-Tuttle. The Perseids are so-called because the point from which they appear to come, called the radiant, lies in the constellation Perseus. Of 225 Geminids observed in 1990 some 38 were blue in color, with one yellow-blue and one blue-green [cyan]. The average pre-atmospheric velocity is 36.2 km/s. "The Broad LAteral Non-imaging Cherenkov Array (BLANCA) takes advantage of the CASA-MIA particle array installation by augmenting it with 144 angle-integrating Cherenkov detectors. Located in Dugway, Utah at an atmospheric depth of 870 g cm−2, BLANCA uses the CASA trigger to collect Cherenkov light and records the Cherenkov lateral distribution from cosmic ray events in the energy range of the knee. The CASA trigger threshold imposes an energy threshold of ∼ 100 TeV on the Cherenkov array. However, BLANCA analysis uses events with a 200 TeV minimum to avoid composition bias introduced from the CASA trigger." "Each BLANCA detector contains a large Winston cone [43] which concentrates the light striking an 880 cm2 entrance aperture onto a photomultiplier tube. The concentrator has a nominal half-angle of 12.5° and truncated length of 60 cm. The Winston cones were aligned vertically with ∼ 0.5° accuracy. A two-output preamplifier increases the dynamic range of the detector. The minimum detectable density of a typical BLANCA unit is approximately one blue photon per cm2." "[A] high-resolution, high-signal-to-noise UV-blue spectrum of the extremely metal-poor red giant HD 88609 [is used] to determine the abundances of heavy elements. Nineteen neutron-capture elements are detected in the spectrum." "[T]his object has large excesses of light neutron-capture elements, while heavy neutron-capture elements are deficient. The abundance pattern shows a continuously decreasing trend as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements." "[T]he abundance pattern found in the two stars could represent the pattern produced by the nucleosynthesis process that provided light neutron-capture elements in the very early Galaxy." "Although the mean metal abundance M/H varies from a factor 12 to 250 relative to the Sun, the abundance of lithium is very constant in all these [halo and old disk] stars, but the coolest ones where the convection zone is deep enough to induce 7Li destruction by proton fusion." "[T]he lithium has a fragile nucleus which is destroyed by proton fusion when the temperature reaches 2 106 K." "[F]or the limit between "halo stars" and "old disk stars", [there is] a discontinuity in the relation δ(U - B) versus [Fe/H] at about [Fe/H] = -1.0 dex ... "halo stars" ... are metal deficient by a factor ranging from 12 to 250 relative to the Sun. ... "old disk stars" ... are metal deficient by a factor ranging from 2 to 10." These well-known metal deficient stars have "high dispersion spectra in the blue wavelength range". "In all the stars analysed ... it is very unlikely that the lithium observed in the atmosphere was produced, even in part, inside the stars themselves, and then transported up into the atmospheres." "[T]he lithium rich stars are not statistically younger than the lithium poor stars." "[H]igh-quality spectrophotometric observations of 10 low-metallicity blue compact galaxies (BCGs) with oxygen abundance ranging from 12 + log(O/H) = 7.37 to 8.04 [are used] to determine the primordial helium abundance." "The main physical mechanism changing the He I line intensities from their recombination values is collisional excitation. To correct for it, we calculate the electron number density in the He+ zone by a self-consistent procedure which constrains the He I λ5876/λ4471, λ6678/λ4471 and λ7065/λ4471 line ratios to have their recombination values, after correction for collisional enhancement." In "the spectrum of a middle-aged [pulsar] PSR B0656+14 [may be] two wide, red and blue, flux depressions whose frequency ratio is about 2 and which could be the 1st and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic fields [of] ~108 G in [the] upper magnetosphere of the pulsar." "On February 23.316 UT, 1987, [blue] light and neutrinos from the brightest supernova in 383 years arrived at Earth ... it has been observed ... at all wavelengths from radio through gamma rays, SN 1987A is the only object besides the Sun to have been detected in neutrinos." At left is an image of supernova SN 1987A, one of the brightest stellar explosions since the invention of the telescope more than 400 years ago. Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak -69° 202, a blue supergiant. This was an unexpected identification, because at the time a blue supergiant was not considered a possibility for a supernova event in existing models of high mass stellar evolution. Many models of the progenitor have attributed the color to its chemical composition, particularly the low levels of heavy elements, among other factors. "For the highest possible rotation rates (about 400 km s-1), a novel sort of evolution is encountered in which single stars mix completely on the main sequence, never becoming red giants. Such stars, essentially massive "blue stragglers," produce helium-oxygen cores that rotate unusually rapidly. Such stars might comprise roughly 1% of all stars above 10 Mʘ and can, under certain circumstances, retain enough angular momentum to make [gamma-ray bursts] GRBs. Because this possibility is very sensitive to mass loss, GRBs are much more probable in regions of low metallicity." "The far-infrared to soft X-ray continuum of radio-quiet and steep-spectrum radio-loud [Palomar-Green (PG) Bright Quasar Survey] PG quasars can be described in a model consisting of two broad peaks: an 'infrared bump' at about 2 microns to 1 mm and the well-known 'big blue bump' at about 10 nm to 0.3 micron." "[T]he distant X-ray emitter Abell cluster A 370 (z = 0.373) [contains] a very particular [blue] ring-like structure of galaxies with a diffuse component lying near one of the very luminous galaxies of the cluster core." The frequency spectrum of Cherenkov radiation by a particle is given by the Frank–Tamm formula. Unlike fluorescence or emission spectra that have characteristic spectral peaks, Cherenkov radiation is continuous. Around the visible spectrum, the relative intensity per unit frequency is approximately proportional to the frequency. That is, higher frequencies (shorter wavelengths) are more intense in Cherenkov radiation. This is why visible Cherenkov radiation is observed to be brilliant blue. In fact, most Cherenkov radiation is in the ultraviolet spectrum—it is only with sufficiently accelerated charges that it even becomes visible; the sensitivity of the human eye peaks at green, and is very low in the violet portion of the spectrum. Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. In addition, whereas red sprites tend to be associated with significant lightning strikes, blue jets do not appear to be directly triggered by lightning (they do, however, appear to relate to strong hail activity in thunderstorms). They are also brighter than sprites and, as implied by their name, are blue in color. The color is believed to be due to a set of blue and near-ultraviolet emission lines from neutral and ionized molecular nitrogen. "Blue starters were discovered on video from a night time research flight around thunderstorms and appear to be "an upward moving luminous phenomenon closely related to blue jets." They appear to be shorter and brighter than blue jets, reaching altitudes of only up to 20 km. Blue starters appear to be blue jets that never quite make it". Plasma cleaning involves the removal of impurities and contaminants from surfaces through the use of an energetic plasma created from gaseous species. Gases such as argon and oxygen, as well as mixtures such as air and hydrogen/nitrogen are used. The plasma is created by using high frequency voltages (typically kHz to >MHz) to ionise the low pressure gas (typically around 1/1000 atmospheric pressure), although atmospheric pressure plasmas are now also common. At left is an image of the Northern Lights on Earth showing the very rare blue lights. The blue hour is the period of twilight each morning and evening where there is neither full daylight nor complete darkness. The time is considered special because of the quality of the light. At first right is a seascape after sunset at Praia da Ursa, Sintra, Portugal, during the blue hour. The first image at left shows the Colosseum in Rome during this blue hour. The second image at right shows the blue hour in Paris around the Eiffel Tower and Pont Alexandre III at night. The second image at left is the Brandenburg Gate in Berlin during the blue hour. The last image at left is the illuminated mining lamp memorial in Moers during the blue hour. The image at right is a detailed, photo-like view of Earth based largely on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. "Viewed from space, the most striking feature of our planet is the water. In both liquid and frozen form, it covers 75% of the Earth’s surface. It fills the sky with clouds. Water is practically everywhere on Earth, from inside the rocky crust to inside our cells." Sin-Kamen (Синь-Камень, in Russian literally – Blue Stone, or Blue Rock) is a type of pagan sacred stones, widespread in Russia, in areas historically inhabited by both Eastern Slavic (Russian), and Uralic tribes (Merya, Muroma). While in the majority of cases, the stones belonging to the Blue Stones type, have a black, or dark gray color, this particular stone [in the image] does indeed look dark blue, when wet. "Several types of rock surface materials can be recognized at the two sites [Viking Lander 1 and Viking Lander 2]; dark, relatively 'blue' rock surfaces are probably minimally weathered igneous rock, whereas bright rock surfaces, with a green/(blue + red) ratio higher than that of any other surface material, are interpreted as a weathering product formed in situ on the rock." At second right is an approximately natural color image of the asteroid 243 Ida. Helium II does have an emission line in the blue at 469 nm. "The Wide Field Camera 3 (WFC3), a new camera aboard NASA's Hubble Space Telescope, snapped this image of the planetary nebula, catalogued as NGC 6302, but more popularly called the Bug Nebula or the Butterfly Nebula. WFC3 was installed by NASA astronauts in May 2009, during the servicing mission to upgrade and repair the 19-year-old Hubble telescope." "What resemble dainty butterfly wings are actually roiling cauldrons of gas heated to more than 36,000 degrees Fahrenheit. The gas is tearing across space at more than 600,000 miles an hour—fast enough to travel from Earth to the Moon in 24 minutes!" "NGC 6302 lies within our Milky Way galaxy, roughly 3,800 light-years away in the constellation Scorpius. The glowing gas is the star's outer layers, expelled over about 2,200 years. The "butterfly" stretches for more than two light-years, which is about half the distance from the Sun to the nearest star, Alpha Centauri." "The central star itself cannot be seen, because it is hidden within a doughnut-shaped ring of dust, which appears as a dark band pinching the nebula in the center. The thick dust belt constricts the star's outflow, creating the classic "bipolar" or hourglass shape displayed by some planetary nebulae." "The star's surface temperature is estimated to be about 400,000 degrees Fahrenheit, making it one of the hottest known stars in our galaxy. Spectroscopic observations made with ground-based telescopes show that the gas is roughly 36,000 degrees Fahrenheit, which is unusually hot compared to a typical planetary nebula." "The WFC3 image reveals a complex history of ejections from the star. The star first evolved into a huge red-giant star, with a diameter of about 1,000 times that of our Sun. It then lost its extended outer layers. Some of this gas was cast off from its equator at a relatively slow speed, perhaps as low as 20,000 miles an hour, creating the doughnut-shaped ring. Other gas was ejected perpendicular to the ring at higher speeds, producing the elongated "wings" of the butterfly-shaped structure. Later, as the central star heated up, a much faster stellar wind, a stream of charged particles traveling at more than 2 million miles an hour, plowed through the existing wing-shaped structure, further modifying its shape." "The image also shows numerous finger-like projections pointing back to the star, which may mark denser blobs in the outflow that have resisted the pressure from the stellar wind." "The nebula's reddish outer edges are largely due to light emitted by nitrogen, which marks the coolest gas visible in the picture. WFC3 is equipped with a wide variety of filters that isolate light emitted by various chemical elements, allowing astronomers to infer properties of the nebular gas, such as its temperature, density, and composition." "The white-colored regions are areas where light is emitted by sulfur. These are regions where fast-moving gas overtakes and collides with slow-moving gas that left the star at an earlier time, producing shock waves in the gas (the bright white edges on the sides facing the central star). The white blob with the crisp edge at upper right is an example of one of those shock waves." "NGC 6302 was imaged on July 27, 2009, with Hubble's Wide Field Camera 3 in ultraviolet and visible light. Filters that isolate emissions from oxygen, helium, hydrogen, nitrogen, and sulfur from the planetary nebula were used to create this composite image." The filters used for this image are F373N ([O II], purple), F469N (He II, blue), F502N ([O III], cyan), F656N (Hα, brown), F658N ([N II], orange), and F673N ([S II], white). The emission and absorption spectra for beryllium contain lines in the blue. The emission and absorption spectra for boron contain lines on the border between violet and blue. Carbon has three emission lines that occur in an electron cyclotron resonance (ECR) heated plasmas: 464.742, 465.025, and 465.147 nm from C III. Nitrogen has two emission lines that occur in plasmas at 455.368 and 455.545 nm from N VII. There is an "(0,2) vibrational component of the B-x electronic transition of N2(+) at 470.9 nm." The spectrum above shows the lines in the visible due to emission from elemental oxygen. The emission and absorption spectra of fluorine contains at least eight lines or bands from the cyan to the ultraviolet. Like fluorine, neon has at least fourteen emission and absorption lines or bands from the cyan to the violet. Argon has an emission line that occurs in an electron cyclotron resonance (ECR) heated plasmas: 473.591 nm from Ar II. Titanium has two emission lines at 456.3757 and 457.1971 nm from Ti II. Chromium has two emission lines at 455.8650 and 458.8199 nm from Cr II. Iron has one emission line at 458.3837 nm from Fe II. Usually, Hibonite ((Ca,Ce)(Al,Ti,Mg)12O19) as shown at right is a brownish black mineral. It is rare, but is found in high-grade metamorphic rocks on Madagascar. Some presolar grains in primitive meteorites consist of hibonite. Hibonite also is a common mineral in the Ca-Al-rich inclusions (CAIs) found in some chondrite or chondritic meteorites. Hibonite is closely related to hibonite-Fe (IMA 2009-027, ((Fe,Mg)Al12O19)) an alteration mineral from the Allende meteorite. [Hibonite] is blue [perhaps like the image at left] in meteorite occurrence. "Grain size varies from 98 to 530 lm with an average of *150 lm. Minor [elements] oxidation [from an iron–nickel–chromium–cobalt–phosphorus alloy] is evidenced by the presence of a light brown and blue surface layer composed of very fine-grained (<1 lm) crystals on the surface." "[T]he oxidation of minor elements in metallic alloys in the early solar system" is indicated to possess at instances a blue surface layer. "If we know beforehand that a nebula is not of the emission type, observations of its polarization enable us to go a step farther. In general, if a particle scatters light in such a way that it does not hold the energy for any length of time but simply defects it without change of wave-length, then the polarization of the deflected light has the following characteristics: (a) its plane of polarization is usually perpendicular to or, more rarely, parallel to the plane formed by the incident and the scattered rays; and (b) the amount of polarization is inversely correlated with the size of the particles. When the scattering particles are of the order of size of a few hundred molecules or smaller we have what is usually known as Rayleigh scattering. Here the polarization reaches very large values, as is evidenced by our own blue atmosphere, which gives values up to 70 per cent." "The depth of the absorption bands and the continuum reflectance of [Kuiper Belt Object] 1996 TO66 suggest the presence of a black- to slightly blue-colored, spectrally featureless particulate material as a minority component mixed with the water ice." "This [image at right] is a false-color, red-green-blue composite view generated from images taken through the Pancam's 750-nanometer, 530-nanometer and 430-nanometer filters. The exaggeraged color is used for enhancing the visibility of differences among the types of rock and soil materials." "Analysis of Block Island's composition using the rover's alpha particle X-ray spectrometer confirmed that it is rich in iron and nickel. The rock is about 60 centimeters (2 feet) across." As an astronomical object sets or rises in relation to the horizon, the light it emits travels through Earth's atmosphere, which works as a prism separating the light into different colors. The color of the upper rim of an astronomical object could go from green to blue to violet depending on the decrease in concentration of pollutants, as they spread throughout an increasing volume of atmosphere. Very occasionally, the amount of blue light is sufficient to be visible as a "blue flash". "MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters. As the spacecraft receded from Mercury after making its closest approach on January 14, 2008, the WAC recorded a 3x3 mosaic covering part of the planet not previously seen by spacecraft. The color image shown here was generated by combining the mosaics taken through the WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet). These three images were placed in the red, green, and blue channels, respectively, to create the visualization presented here. The human eye is sensitive only across the wavelength range from about 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in black-and-white (single-color) images." "Color differences on Mercury are subtle, but they reveal important information about the nature of the planet's surface material. A number of bright spots with a bluish tinge are visible in this image. These are relatively recent impact craters. Some of the bright craters have bright streaks (called "rays" by planetary scientists) emanating from them. Bright features such as these are caused by the presence of freshly crushed rock material that was excavated and deposited during the highly energetic collision of a meteoroid with Mercury to form an impact crater. The large circular light-colored area in the upper right of the image is the interior of the Caloris basin. Mariner 10 viewed only the eastern (right) portion of this enormous impact basin, under lighting conditions that emphasized shadows and elevation differences rather than brightness and color differences. MESSENGER has revealed that Caloris is filled with smooth plains that are brighter than the surrounding terrain, hinting at a compositional contrast between these geologic units. The interior of Caloris also harbors several unusual dark-rimmed craters, which are visible in this image. The MESSENGER science team is working with the 11-color images in order to gain a better understanding of what minerals are present in these rocks of Mercury's crust." In the image at right the whiter cloud areas have a bluish tint. This is a real-color image of Venus processed through the clear and blue filters onboard Mariner 10. "Earth is a blue planet". Atmospheric gases scatter blue light more than other wavelengths, giving the Earth a blue halo when seen from space. This is shown in the image at right. When light passes through our atmosphere, photons interact with it through scattering. If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you cannot see your shadow there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering, shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal to reach your eye. Much of the blue light has been scattered out, leaving the red light in a sunset. The bluish color of water is a composite of several contributing agents. Prominent contributors include dissolved organic matter and chlorophyll. The third image at right is the famous Blue Marble image of Earth taken by Apollo 17. The image shows the eastern Southern Atlantic Ocean, the South African portion of the Southern Ocean, and the Western Indian Ocean. The land consists of most of Africa, Madagascar, Saudi Arabia, and portions of Iran, Irag, Turkey, and southern Greece. The gaseous portion consists of water vapor clouds over the southern portion of this hemisphere. Antarctica is completely covered in snow (a water ice rocky substance). If this third image is the one chosen to decide whether the Earth is a dwarf gaseous object, a dwarf liquid object, or a dwarf rocky object, the decision becomes difficult. Here, the Earth is primarily a liquid body. "Nine out of 10 well-characterized Apollo 17 breccia matrices fall into Group 2, and this includes both the blue-grey breccias which are the dominant rock type at this site". "A 1953 telescopic photograph of a flash on the Moon is the only unequivocal record of the rare crash of an asteroid-sized body onto the lunar surface. ... A search of images from the Clementine mission reveals an ∼1.5-km high-albedo, blue, fresh-appearing crater with an associated ejecta blanket at the location of the flash." In terms of reflectance from the lunar surface, "the very dark 'blue' maria [are] such as found in Mare Tranquillitatis." "[T]he slope of the reflectance spectrum in the blue and ultraviolet ... is directly related to the percent TiO2 in the [lunar] surface soil (Charette et al., 1974)." "The Mast Camera (Mastcam) on NASA's Mars rover Curiosity showed researchers interesting internal color in this rock called "Sutton_Inlier," which was broken by the rover driving over it. The Mastcam took this image during the 174th Martian day, or sol, of the rover's work on Mars (Jan. 31, 2013). The rock is about 5 inches (12 centimeters) wide at the end closest to the camera. This view is calibrated to estimated "natural" color, or approximately what the colors would look like if we were to view the scene ourselves on Mars. The inside of the rock, which is in the "Yellowknife Bay" area of Gale Crater, is much less red than typical Martian dust and rock surfaces, with a color verging on grayish to bluish." "[T]he Chemistry and Camera (ChemCam) instrument zapped [the rock known as "Jake Matijevic"] with its laser on Sept. 21, 2012, and Sept. 24, 2012, which were the 45th and 48th sol, or Martian day of operations. ... black and white images were taken by ChemCam to look for the pits produced by the laser. ... [Later] the Alpha Particle X-ray Spectrometer trained its view. ... This image was obtained by Curiosity's Mast Camera on Sept. 21, 2012 PDT (Sept. 22 UTC), or sol 46. [For natural color, processors] white-balanced the color in this view to increase the inherent differences visible within the rock." Other bluish rocks can just be seen. Curiosity removed the Martian dust from "Jake Matijevic" before photographing. "On Sol 20 of its journey, Mars Exploration Rover Opportunity woke up around 5:30 in the martian afternoon to watch the sunset. A series of five sets of three-color images from the rover's panoramic camera was acquired looking toward the southwest. Each set used an infrared, green and violet filter, rather than the human red-green-blue, so that the maximum panoramic camera wavelength range could be covered by the observations, enhancing the scientific value of the measurements." "A color image was made [at lower right] from the first post-sunset sequence of calibrated color images, with the color balance set to approximate what the sunset color would have looked like to the human eye. The color seen in this first post-sunset image was then used to colorize each image in the sequence. Approximately one-minute gaps between consecutive color images meant the Sun's position changed within each color set, so the images had to be manually shifted to compensate for this motion. In this fashion, the position and brightness of the Sun are taken from each individual image, but the color is taken from a single set of images. The images were then combined into a movie where one color set fades gracefully into the next. Analysis of the five color sets shows that there were only small color variations during the sunset, so most of the real variations are captured in the movie." "The rapid dimming of the Sun near the horizon is due to the dust in the sky. There is nearly twice as much dust as there was when the Mars Pathfinder spacecraft, which landed on Mars in 1997, imaged the sunset. This causes the Sun to be many times fainter. The sky above the Sun has the same blue tint observed by Pathfinder and also by Viking, which landed on Mars in 1976. This is because dust in the martian atmosphere scatters blue light forward toward the observer much more efficiently than it scatters red light forward. Therefore, a "halo" of blueish sky color is always observed close to the Sun. We're only seeing half of this halo in the movie, because the other half is below the horizon." At second left is an image in natural color by the HiRISE camera of Cerberus Fossae Graben showing exposed blue material. The third image at right shows "the eastern (west-facing) side of an impact crater in the mid-latitudes of the Northern hemisphere." "Like many mid-latitude craters, this one has gullies along its walls that are composed of alcoves, channels, and debris aprons. The origins of these gullies have been the subject of much debate; they could have formed by flowing water, liquid carbon dioxide, or dry granular flows. The orientation of these gullies is of interest because many craters only contain gullies on certain walls, such as those that are pole-facing. This could be due to changes in orbital conditions and differences in solar heating along specific walls." "Many of the other features observed in and around this crater however are indicative of an ice-rich terrain, which may lend credence to the water formation hypothesis, at least for the gullies visible here. The most notable of these features is the "scalloped" terrain in and around the crater. This type of terrain has been interpreted as a sign of surface caving, perhaps due to sublimation of underlying ice. (Sublimation is the process of a solid changing directly to a gas.)" "Another sign of ice is the presence of parallel lineations and pitted material on the floor of the crater, similar to what is referred to as concentric crater fill. Parallel linear cracks are also observed along the crater wall over the gullies, which could be due to thermal contraction of ice-rich material." "All of these features taken together are evidence for ice-rich material having been deposited in this region during different climatic conditions that has subsequently begun to melt and/or sublimate under current conditions. More recently, aeolian deposits have accumulated around the crater as evidenced by the parallel ridges dominating the landscape. Dust devil streaks are also visible crossing the aeolian ridges." The image at third left "shows part of the floor of Rabe Crater, a large (108 kilometre diameter) impact crater in the Southern highlands". "Dark dunes—accumulations of wind blown sand—cover part of crater's floor, and contrast with the surrounding bright-colored outcrops. The extreme close-up view reveals a thumbprint-like texture of smaller ridges and troughs covering the surfaces of the larger dunes. These smaller ripples are also formed and shaped by blowing wind in the thin atmosphere of Mars." "One puzzling question is why the dunes are dark compared with the relative bright layered material contained within the crater. The probable answer is that the source of the dark sand is not local to this crater; rather, this topographic depression has acted as a sand trap that has collected material being transported by winds blowing across the plains outside the crater." The fourth image at right shows "pristine gullies, some with bright deposits, and perhaps very recent." "In addition, there is exposed bedrock, which at HiRISE resolution, we can pick out fine details. Observations like this can also help gully modeling." The fourth image at left shows an example of "[d]unes of sand-sized materials have been trapped on the floors of many Martian craters. This is one ... from a crater in Noachis Terra, west of the giant Hellas impact basin. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter captured this view on Dec. 28, 2009." "The dunes here are linear, thought to be due to shifting wind directions. In places, each dune is remarkably similar to adjacent dunes, including a reddish (or dust colored) band on northeast-facing slopes. Large angular boulders litter the floor between dunes." The fifth image at right shows layered rocks on the floor of McLaughlin Crater. These "sedimentary rocks ... contain spectroscopic evidence for minerals formed through interaction with water. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded the image." "A combination of clues suggests this 1.4-mile-deep (2.2-kilometer-deep) crater once held a lake fed by groundwater. Part of the evidence is identification of clay and carbonate minerals within layers visible near the center of this image. The mineral identifications come from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), also on the Mars Reconnaissance Orbiter. The scene covers an area about one-third of a mile (about 550 meters) across, at 337.6 degrees east longitude, 21.9 degrees north latitude. North is up." The fifth left image is a partial image of a recent impact crater on Mars captured by HiRISE. Although the HiRISE image does not show the entire crater, note that below the top rock layers cut through by the meteor is a blue layer. Some portions of this layer have slide down the crater wall beneath the layer. This suggests that the blue material is a layer beneath an outer Martian crust. The fifth image on the right shows Martian blueberries discovered during the Opportunity mission to Mars. Martian spherules are the abundant spherical hematite inclusions discovered by the Mars Exploration Rover (Opportunity rover) at Meridiani Planum. The Mars Global Surveyor Thermal Emission Spectrometer (TES) first detected "crystalline hematite (α‐Fe 2O 3)” within Sinus Meridiani from orbit. The presence of hematite was confirmed after the Opportunity rover landed in Meridiani Planum. The moniker "blueberries" was coined by the original science team due to the hematite appearing blue relative to the surrounding media in the "natural color RGB images" analyzed. A number of straightforward geological processes can yield round shapes, including accretion under water, meteor impacts, or volcanic eruptions. They could alternately be concretions, or accumulated material, formed by minerals coming out of solution as water diffused through rock. The blueberries from Eagle Crater to Endurance (crater) were found that in a sample of 696 blueberries, disregarding any non-spherical blueberries from the sample, the blueberries average major axis to be about 2.87 mm (just over 1/10th inch), blueberries that are found within soils are typically smaller than blueberries found in the outcrops, the size of the blueberries tends to decrease with decreasing latitude. Many fragmented blueberries suggest the fracturing occurred after spherule formation, which may either be from meteoric impacts, or the "same process" that "fractured the outcrop"; however, this would not explain the presence of the smallest hematite spherules detected which are close to perfectly spherical and therefore cannot be explained by fracturing or erosion. Blueberries uncovered by the Rock Abrasion Tool aboard Opportunity were about 4 mm (0.16 inches) semi-major axis length at Eagle Crater and Endurance crater, about 2.2mm (0.087 inches) at Vostok, and about 3.0 mm (0.12 inches) at Naturaliste (crater), found in "the plains" were smaller (1-2mm or 0.04-0.08 inches) than those of Eagle and Endurance craters. "The Martian blueberries, first discovered by NASA’s Opportunity rover, are concretions likely formed in sediments from hydrothermal solutions resulting from bolide impact into groundwater or permafrost. Evidence for this conclusion comes from the shapes of particle size distributions measured from Opportunity photos by Royer et al. (2006, 2008). These distributions, which exhibit a unique negative skew and lognormal positive skews, fit theoretical and experimental shapes determined for minerals precipitated from solution at higher and lower levels of supersaturation, respectively." Pallas, minor-planet designation 2 Pallas, is the second asteroid to have been discovered (after Ceres), and one of the largest in the Solar System. It is estimated to comprise 7% of the mass of the asteroid
{'wiki_source': 'wikiversity', 'other_info': "{'content_model': 'wikitext', 'language': 'en', 'title': 'Radiation astronomy/Blues', 'type': 'text'}"}