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Radiation astronomy/Objects

< Radiation astronomy
This true-color image shows North and South America as they would appear from space 35,000 km (22,000 miles) above the Earth. Credit: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC.

The science of radiation astronomy often focuses on natural objects in the sky about which physical and logical laws may be obtained. These radiation astronomy objects or radiation objects are found very close to our home on Draft:Earth and include the Earth itself and the Draft:Moon.

Initially looking as close to home as possible should uncover local objects that are sources of radiation in various forms.

The SIMBAD reference database "contains identifications, 'basic data', bibliography, and selected observational measurements for several million astronomical objects."[1]

"The specificity of the SIMBAD database is to organize the information per astronomical object".[1] "Building a reference database for ... all astronomical objects outside the Solar System – has been the first goal of the CDS".[1] "The only astronomical objects specifically excluded from SIMBAD are the Sun and Solar System bodies."[1]

As indicated in the learning resource Draft:astronomy, there are many objects between the observer on the ground atop some portion of the Earth's crust, astronomical objects such as the Sun and Solar System bodies, and those beyond the limits of the solar system. Further, for those observers looking toward the Earth from another location such as near the Moon, it seems that the Earth is a natural object.

Astronomical objects that radiate, reflect, or fluoresce may range in size from individual atoms or subatomic particles to rocky objects, gaseous objects, or plasma objects, including those that are composites.

Astronomical objects are likely to have a discrete form that separates them from the electromagnetic background.

Contents

Theoretical radiation objectsEdit

Theoretical astronomy provides a definition (Def.) of an object in astronomy:

Def. a natural object in the sky especially at night is called an astronomical object.

ObjectsEdit

 
This is a photograph taken in 1910 during the passage of Halley's comet. Credit: The Yerkes Observatory.
 
A photo of the planet Mars is taken in Straßwalchen (Austria) on September 19, 2003, shortly after its closest approach. Credit: Rochus Hess, http://members.aon.at/astrofotografie.
 
The Earth and Moon is imaged by the Mars Global Surveyor on May 8, 2003, at 12:59:58 UTC.
 
The Chicxulub impact crater is outlined. Credit: NASA/JPL-Caltech, modified by David Fuchs.
 
The telescope photograph of the Great Andromeda Nebula is taken around 1899. Credit: Isaac Roberts.

A celestial object is any astronomical object except the Earth.

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.

Some objects seem to wander around in the night sky relative to many of the visual points of light. At least one occasionally is present in the early morning before sunrise as the Morning Star and after sunset as the Evening Star, the planet Draft:Venus. These wanderers and related objects are subjects for observational astronomy and some are meteors.

Others only make an appearance after decades, sometimes spectacularly.

"The 1910 approach, which came into naked-eye view around 10 April[2] and came to perihelion on 20 April,[2] was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained.[3] Furthermore, the comet made a relatively close approach of 0.15AU,[2] making it a spectacular sight. Indeed, on 19 May, the Earth actually passed through the tail of the comet.[4][5] One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen,[6] which led astronomer Camille Flammarion to claim that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet."[7] His pronouncement led to panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.[8] In reality, as other astronomers were quick to point out, the gas is so diffuse that the world suffered no ill effects from the passage through the tail.[7]"[9]

"It is quite possible that [faint streamers preceding the main tail and lying nearly in the prolonged radius vector] may have touched the Earth, probably between May 19.0 and May 19.5, [1910,] but the Earth must have passed considerably to the south of the main portion of the tail [of Halley's comet]."[10]

Of the other planets of the solar system, Draft:Mercury, Draft:Mars, Draft:Jupiter, Draft:Saturn, Draft:Uranus, and Draft:Neptune, none has apparently produced as much drama and excitement recently on Earth among some of the intelligent life forms as Halley's comet.

According to the Wikipedia article on the planet Mars: "Mars made its closest approach to Earth and maximum apparent brightness in nearly 60,000 years, 55,758,006 km (0.372719 [Astronomical unit] AU), magnitude −2.88, on 27 August 2003 at 9:51:13 UT."

But asteroid impacts, though rare, occur once in a while, over very large areas, at aperiodic intervals such as the Chicxulub crater. Most scientists agree that this impact is the cause of the Cretatious-Tertiary Extinction, 65 million years ago (Ma), that marked the sudden extinction of the dinosaurs and the majority of life then on Earth. This shaded relief image of Mexico's Yucatan Peninsula shows a subtle, but unmistakable, indication of the Chicxulub impact crater.

Still much further away from the Earth than the Sun or Neptune are the many stars and nebulae that make up the Milky Way. Beyond the confines of our galaxy is the Andromeda Galaxy.

Of the Local Group, “[i]ts two dominant galaxies, the Milky Way and Andromeda (M31), are separated by a distance of ~700 kpc and are moving toward each other with a radial velocity of about -117 km s-1 (Binney & Tremaine 1987, p. 605).”[11] "making [Andromeda] one of the few blueshifted galaxies. The Andromeda Galaxy and the Milky Way are thus expected to collide in about 4.5 billion years, although the details are uncertain since Andromeda's tangential velocity with respect to the Milky Way is only known to within about a factor of two.[12] A likely outcome of the collision is that the galaxies will merge to form a giant elliptical galaxy.[13] Such events are frequent among the galaxies in galaxy groups. The fate of the Earth and the Solar System in the event of a collision are currently unknown. If the galaxies do not merge, there is a small chance that the Solar System could be ejected from the Milky Way or join Andromeda.[14]

The various objects and entities that are observed and studied that do not appear to cause us harm also engender separate areas within astronomy, some of which are

  1. Extragalactic astronomy,
  2. Galactic astronomy,
  3. Physical cosmology,
  4. Planetary science,
  5. Solar astronomy, and
  6. Stellar astronomy.

Strong forcesEdit

 
This image shows an example of a bipolar planetary nebula known as PN Hb 12 in Cassiopeia. Credit: NASA, ESA, and A. Zijlstra (The University of Manchester).

"Hubble astronomers have found an unexpected surprise while surveying more than 100 planetary nebulae in the central bulge of our Milky Way galaxy. Those nebulae that are butterfly-shaped or hourglass-shaped tend to be mysteriously aligned such that their rotation axis is perpendicular to the plane of our galaxy."[15]

"Astronomers have used the NASA/ESA Hubble Space Telescope and ESO's New Technology Telescope to explore more than 100 planetary nebulae in the central bulge of our galaxy. They have found that butterfly-shaped members of this cosmic family tend to be mysteriously aligned — a surprising result given their different histories and varied properties."[16]

"Planetary nebulae are the expanding gaseous shrouds encircling dying stars. A subset of this population has bipolar outflows that align to the star's rotation axis. Such nebulae formed in different places and have different characteristics and so it is a puzzle why they should always point on the same sky direction, like bowling pins set up in an alley."[15]

"All these nebulae formed in different places and have different characteristics. Neither the individual nebulae, nor the stars that formed them, interact with other planetary nebulae. However, a new study by astronomers from the University of Manchester, UK, now shows surprising similarities between some of these nebulae: many of them line up in the sky in the same way. The "long axis" of a bipolar planetary nebula slices though the wings of the butterfly, whilst the "short axis" slices through the body."[16]

"The astronomers looked at 130 planetary nebulae in the Milky Way's central bulge. They identified three different types, and peered closely at their characteristics and appearance. The shapes of the planetary nebula images were classified into three types, following conventions: elliptical, either with or without an aligned internal structure, and bipolar."[16]

"This really is a surprising find and, if it holds true, a very important one, [...] Many of these ghostly butterflies appear to have their long axes aligned along the plane of our galaxy. By using images from both Hubble and the NTT we could get a really good view of these objects, so we could study them in great detail."[16]

"While two of these populations were completely randomly aligned in the sky, as expected, we found that the third — the bipolar nebulae — showed a surprising preference for a particular alignment, [...] While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected."[15]

"Planetary nebulae are thought to be sculpted by the rotation of the star system from which they form. This is dependent on the properties of this system — for example, whether it is a binary [A binary system consists of two stars rotating around their common centre of gravity.], or has a number of planets orbiting it, both of which may greatly influence the form of the blown bubble. The shapes of bipolar nebulae are some of the most extreme, and are thought to be caused by jets blowing mass outwards from the star system perpendicular to its orbit."[15]

"The alignment we're seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge, [...] For them to line up in the way we see, the star systems that formed these nebulae would have to be rotating perpendicular to the interstellar clouds from which they formed, which is very strange."[16]

"While the properties of their progenitor stars do shape these nebulae, this new finding hints at another more mysterious factor. Along with these complex stellar characteristics are those of our Milky Way; the whole central bulge rotates around the galactic centre. This bulge may have a greater influence than previously thought over our entire galaxy — via its magnetic fields. The astronomers suggest that the orderly behaviour of the planetary nebulae could have been caused by the presence of strong magnetic fields as the bulge formed."[16]

"Researchers suggest that there is something bizarre about star systems within the central hub of our galaxy. They would all have to be rotating perpendicular to the interstellar clouds from which they formed. At present, the best guess is that the alignment is caused by strong magnetic fields that were present when the galactic bulge formed billions of years ago."[15]

"As such nebulae closer to home do not line up in the same orderly way, these fields would have to have been many times stronger than they are in our present-day neighbourhood. Very little is known about the origin and characteristics of the magnetic fields that were present in our galaxy when it was young, so it is unclear how they have changed over time."[16]

"We can learn a lot from studying these objects, [...] If they really behave in this unexpected way, it has consequences for not just the past of individual stars, but for the past of our whole galaxy."[15]

NebulasEdit

 
This image of the Crab Nebula is the result of long exposures in the Red, Blue, Green. Credit: Chris Schur.

"This unusual image [at right of the Crab Nebula] is the result of long exposures in the Red, Blue, Green [including Hα], and a separate set of exposures on the inner continuum radiation with RGB and polarizers crossed 120 degrees for each color. The result is an inner region that is mapped in polarization according to color. The outer filaments are primarily HII and OIII regions and have no polarization. The Object: The Crab Nebula in Taurus is a super nova remnant that exploded in the year 1084 AD and has been rapidly expanding ever since. It is located a degree from the easternmost star in the Bulls horns, and glows dimly at a magnitude of 8.4. While small at 6 arc minutes, it is typical of the [telescope image] size of many galaxies".[17]

Cosmic raysEdit

"Comparison with the chemical composition of various astrophysical objects, such as the Sun, the Draft:interstellar medium, supernovae or neutron stars, can give clues about the site at which cosmic rays are injected into the acceleration process."[18]

NeutralsEdit

 
The Necklace Nebula glows brightly in this Nasa Hubble Space Telescope image. Credit: NASA.

"A giant cosmic necklace glows brightly in this Nasa Hubble Space Telescope image."[19]

"The object, aptly named the Necklace Nebula, is a recently discovered planetary nebula, the glowing remains of an ordinary, sun-like star."[19]

"The nebula consists of a bright ring, measuring 12trillion miles wide, dotted with dense, bright knots of gas that resemble diamonds in a necklace."[19]

"Newly discovered: The Necklace Nebula glows brightly in this composite image taken by the Hubble Space Telescope last month. The glow of hydrogen, oxygen, and nitrogen are shown by the colours blue, green and red respectively".[19]

"It is located 15,000 light-years away in the constellation Sagitta."[19]

"A pair of stars orbiting close together produced the nebula, also called PN G054.2-03.4."[19]

"About 10,000 years ago, one of the ageing stars ballooned to the point where it engulfed its companion star. The smaller star continued orbiting inside its larger companion, increasing the giant’s rotation rate. The bloated companion star spun so fast that a large part of its gaseous envelope expanded into space. Due to centrifugal force, most of the gas escaped along the star’s equator, producing a ring. The embedded bright knots are dense gas clumps in the ring. The pair is so close, only a few million miles apart, that they appear as one bright dot in the centre. The stars are furiously whirling around each other, completing an orbit in a little more than a day."[19]

NeutronsEdit

"[G]alactic (X-ray pulsars, binary systems - black hole candidates) and extragalactic (blasars) objects [emit] gamma-rays [in periodical processes] and high-energy neutral radiation (gamma-rays, neutrons) [is emitted from] solar flares."[20]

"[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."[21]

"[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."[21]

"[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."[21]

PositronsEdit

"It is possible that the X-ray continuum is primary while the radio and optical emission are secondary for all BL Lac objects when the effect of relativistic beaming is considered. Pair production is a possible mechanism for producing X-ray emissions, while the optical and radio emission would be a consequence of this model (Zdziarski & Lightman 1985; Svensson 1986; Fabian et al. 1986). Barr & Mushotzky (1986) showed a significant correlation between the X-ray luminosity and timescale of X-ray variability for Seyfert galaxies and quasars and interpreted this as evidence that the emitting plasma is near the limit of being dominated by electron-positron pairs."[22]

NeutrinosEdit

 
Supernova SN 1987A is one of the brightest stellar explosions since the invention of the telescope more than 400 years ago.[23] Credit: ESA/Hubble & NASA.

Since many neutrinos [are assumed to] come from stellar cores and supernovae, they are released at great temperature/energy. As neutrinos do not interact with matter electromagnetically, they are by definition dark matter.

"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."[24]

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.[25]

Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak -69° 202, a blue supergiant.[26] 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.[24]

Gamma raysEdit

 
This is an image of quasar 3C 279 in gamma rays. Credit: NASA EGRET Compton observatory team.

Over the entire celestial sphere, SIMBAD currently records 3253 gamma-ray objects. Some of these, like 4U 1705-44, are low-mass X-ray binaries (LMXBs). Some, like V779 Centauri, are high-mass X-ray binaries (HXMBs). Others are quasi-stellar objects (PKS 1326-697), supernova remnants (SNRs) like Messier 1 (M 1), and Seyfert galaxies like M 98. Some gamma-ray emitting objects have not been sufficiently resolved to determine what they are.

Def. very high frequency (and therefore very high energy) electromagnetic radiation emitted as a consequence of radioactivity is called a gamma ray.

Def. electromagnetic radiation consisting of gamma rays is called gamma radiation.

Gamma rays typically have frequencies above 10 exahertz (or >1019 Hz), and therefore have energies above 100 keV and wavelengths less than 10 picometers (less than the diameter of an atom). However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes. Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay. Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV. In astronomy, gamma rays are defined by their energy, and no production process need be specified. The energies of gamma rays from astronomical sources range over 10 TeV, at a level far too large to result from radioactive decay. A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay.

"The unusually wide span of the gamma-ray spectral window [covers] at least ten decades of photon energies (~105 - 1015 eV)".[27]

The Rosemary Hill Observatory (RHO) started observing 3C 279 in 1971,[28] and was further observed by the Compton Gamma Ray Observatory in 1991, when it was unexpectedly discovered to be one of the brightest gamma ray objects in the sky.[29] It is also one of the most bright and variable sources in the gamma ray sky monitored by the Fermi Space Telescope. Apparent superluminal motion was detected during observations first made in 1973 in a jet of material departing from the quasar, though it should be understood that this effect is an optical illusion caused by naive estimations of the speed, and no truly superluminal motion is occurring.[30]

Markarian (Mrk) 1501 is the first Seyfert I galaxy to have superluminal motion.[31] Mrk 1501 is an ultraviolet, X-ray, and gamma-ray source.

Hard gamma raysEdit

 
Emergence of IC 310 is captured in a series of images. Credit: A. Neronov et al. and NASA/DOE/LAT collaboration.

"Fermi's Large Area Telescope (LAT) scans the entire sky every three hours, continually deepening its portrait of the sky in gamma rays, the most energetic form of light. While the energy of visible light falls between about 2 and 3 electron volts, the LAT detects gamma rays with energies ranging from 20 million to more than 300 billion electron volts (GeV)."[32]

"At higher energies, gamma rays are rare. Above 10 GeV, even Fermi's LAT detects only one gamma ray every four months from some sources."[32]

"Any object producing gamma rays at these energies is undergoing extraordinary astrophysical processes. More than half of the 496 sources [the Fermi hard-source list] in the new census are active galaxies, where matter falling into a supermassive black hole powers jets that spray out particles at nearly the speed of light."[32]

"One example is the well-known radio galaxy NGC 1275 [above left], which is a bright, isolated source below 10 GeV. At higher energies it fades appreciably and another nearby source begins to appear. Above 100 GeV, NGC 1275 becomes undetectable by Fermi, while the new source, the radio galaxy IC 310, shines brightly."[32]

"The catalog serves as an important roadmap for ground-based facilities called Atmospheric Cherenkov Telescopes, which have amassed about 130 gamma-ray sources with energies above 100 GeV. They include the Major Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in the Canary Islands, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia."[32]

Soft gamma raysEdit

 
A view of 4C 71.07 from observations by the Burst and Transient Source Experiment. Credit: Mike McCollough, USRA.

On the right is a "view of 4C 71.07 from observations by the Burst and Transient Source Experiment. This helped convince scientists that they were studying data from the quasar and not some other source in the neighborhood."[33]

"Angela [Malizia] has now discovered this quasar in soft gamma rays."[34]

"It is also known as QSO 0836+710, a quasar or quasi-stellar object that emits baffling amounts of radio energy. (The numbers actually designate the same place in the sky: 71.07 is its declination, and 0836+710 is right ascension and declination.)"[33]

"It's basically the nucleus of a galaxy that is showing extraordinary activity."[34]

"What BATSE has discovered is that it can be a soft gamma-ray source."[34]

"This makes it the faintest and most distant object to be observed in soft gamma rays. 4C 71.07 has already been observed in gamma rays by the Energetic Gamma Ray Telescope (EGRET) also aboard the Compton Gamma Ray Observatory."[33]

"In the case of 4C 71.07, it's the brightest AGN seen above 20,000 electron volts (20 keV). Its average flux (the amount of radiation reaching our telescopes) is about 13 milliCrabs, or 13/1,000ths as much as the Crab Nebula, a standard candle in astrophysics."[33]

X-raysEdit

Many astronomical objects when studied with visual astronomy may not appear to also be X-ray objects.

The SIMBAD database "contains identifications, 'basic data', bibliography, and selected observational measurements for several million astronomical objects."[1] Among these are some 209,612 astronomical X-ray objects. This information is found by going to the SIMBAD cite listed under 'External links', clicking on "Criteria query" and entering into the box "otype='X'", without the quotes, for an 'object count', and clicking on 'submit query'.

"It is possible that the X-ray continuum is primary while the radio and optical emission are secondary for all BL Lac objects when the effect of relativistic beaming is considered. Pair production is a possible mechanism for producing X-ray emissions, while the optical and radio emission would be a consequence of this model (Zdziarski & Lightman 1985; Svensson 1986; Fabian et al. 1986). Barr & Mushotzky (1986) showed a significant correlation between the X-ray luminosity and timescale of X-ray variability for Seyfert galaxies and quasars and interpreted this as evidence that the emitting plasma is near the limit of being dominated by electron-positron pairs."[22]

UltravioletsEdit

A PG 1159 star, often also called a pre-degenerate,[35] is a star with a hydrogen-deficient atmosphere which is in transition between being the central star of a planetary nebula and being a hot white dwarf. These stars are hot, with surface temperatures between 75,000 K and 200,000 K,[36] and are characterized by atmospheres with little hydrogen and absorption lines for helium, carbon and oxygen. The PG 1159 stars are named after their prototype, PG 1159-035. This star, found in the Palomar-Green survey of ultraviolet-excess stellar objects,[37] was the first PG 1159 star discovered.

Near ultravioletsEdit

 
This composite image shows Z Camelopardalis, or Z Cam, a double-star system featuring a collapsed, dead star, called a white dwarf, and a companion star, as well as a ghostly shell around the system. Credit: NASA/JPL-Caltech/M. Seibert(OCIW)/T. Pyle(SSC)/R. Hurt(SSC).

"This composite image [on the right] shows Z Camelopardalis, or Z Cam, a double-star system featuring a collapsed, dead star, called a white dwarf, and a companion star, as well as a ghostly shell around the system. The massive shell provides evidence of lingering material ejected during and swept up by a powerful classical nova explosion that occurred probably a few thousand years ago."[38]

"The image combines data gathered from the far-ultraviolet and near-ultraviolet detectors on NASA's Galaxy Evolution Explorer on Jan. 25, 2004. The orbiting observatory first began imaging Z Cam in 2003."[38]

"Z Cam is the largest white object in the image, located near the center. Parts of the shell are seen as a lobe-like, wispy, yellowish feature below and to the right of Z Cam, and as two large, whitish, perpendicular lines on the left."[38]

"Z Cam was one of the first known recurrent dwarf nova, meaning it erupts in a series of small, "hiccup-like" blasts, unlike classical novae, which undergo a massive explosion."[38]

The "huge shell around Z Cam [...] it could only be explained as the remnant of a full-blown classical nova explosion. This finding provides the first evidence that some binary systems undergo both types of explosions. Previously, a link between the two types of novae had been predicted, but there was no evidence to support the theory."[38]

"The faint bluish streak in the bottom right corner of the image is ultraviolet light reflected by dust that may or may not be related to Z Cam."[38]

"The yellow objects are strong near-ultraviolet emitters; blue features have strong far-ultraviolet emission; and white objects have nearly equal amounts of near-ultraviolet and far-ultraviolet emission."[38]

OpticalsEdit

Sample calibration colors[39]
Class B–V U–B V–R R–I Teff (K)
O5V –0.33 –1.19 –0.15 –0.32 42,000
B0V –0.30 –1.08 –0.13 –0.29 30,000
A0V –0.02 –0.02 0.02 –0.02 9,790
F0V 0.30 0.03 0.30 0.17 7,300
G0V 0.58 0.06 0.50 0.31 5,940
K0V 0.81 0.45 0.64 0.42 5,150
M0V 1.40 1.22 1.28 0.91 3,840

The color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. To measure the index, one observes the magnitude of an object successively through two different filters, such as U and B, or B and V, where U is sensitive to ultraviolet rays, B is sensitive to blue light, and V is sensitive to visible (green-yellow) light (see also: UBV system). The set of passbands or filters is called a photometric system. The difference in magnitudes found with these filters is called the U-B or B–V color index, respectively. The smaller the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is. This is a consequence of the logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the yellowish Sun has a B–V index of 0.656 ± 0.005,[40] while the bluish Rigel has B–V –0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B–V = –0.03).[41] The passbands most optical astronomers use are the UBVRI filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes infrared light. ... These filters were specified as particular combinations of glass filters and photomultiplier tubes.

A Photometric system is a set of well-defined passbands (or filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided.

Filter Letter Effective Wavelength Midpoint λeff For Standard Filter[42] Full Width Half Maximum[42] Variant(s) Description
Ultraviolet
U 365nm 66nm u, u', u* "U" stands for ultraviolet.
Visible
B 445nm 94nm b "B" stands for blue.
V 551nm 88nm v, v' "V" stands for visual.
G g, g' "G" stands for green (visual).
R 658nm 138nm r, r', R', Rc, Re, Rj "R" stands for red.
Near-Infrared
I 806nm 149nm i, i', Ic, Ie, Ij "I" stands for infrared.

BluesEdit

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.

CyansEdit

 
Images of Hanny's Voorwerp in Leo Minor and IC 2497 are taken by the Wide Field Camera 3 of the Hubble Space Telescope. Credit: NASA, ESA, W. Keel (University of Alabama), and the Galaxy Zoo Team.

The image at right contains IC 2497, the galaxy near the image top, and "an unusual, ghostly green blob of gas [that] appears to float near a normal-looking spiral galaxy."[43]

"The bizarre object, dubbed Hanny's Voorwerp (Hanny's Object in Dutch), is the only visible part of a 300,000-light-year-long streamer of gas stretching around the galaxy, called IC 2497. The greenish Voorwerp is visible because a searchlight beam of light from the galaxy's core illuminated it. This beam came from a quasar, a bright, energetic object that is powered by a black hole. The quasar may have turned off about 200,000 years ago."[43]

"This Hubble view uncovers a pocket of star clusters, the yellowish-orange area at the tip of Hanny's Voorwerp. The star clusters are confined to an area that is a few thousand light-years wide. The youngest stars are a couple of million years old. The Voorwerp is the size of our Milky Way galaxy, and its bright green color is from glowing oxygen."[43]

"Hubble also shows that gas flowing from IC 2497 may have instigated the star birth by compressing the gas in Hanny's Voorwerp. The galaxy is located about 650 million light-years from Earth."[43]

"What appears to be a gaping hole in Hanny's Voorwerp actually may be a shadow cast by an object in the quasar's light path. The feature gives the illusion of a hole about 20,000 light-years wide. Hubble reveals sharp edges but no other changes in the gas around the apparent opening, suggesting that an object close to the quasar may have blocked some of the light and projected a shadow on the Voorwerp. This phenomenon is similar to a fly on a movie projector lens casting a shadow on a movie screen."[43]

"An interaction between IC 2497 and another galaxy about a billion years ago may have created Hanny's Voorwerp and fueled the quasar. The Hubble image shows that IC 2497 has been disturbed, with complex dust patches, warped spiral arms, and regions of star formation around its core. These features suggest the aftermath of a galaxy merger. The bright spots in the central part of the galaxy are star-forming regions. The small, pinkish object to the lower right of IC 2497 is an edge-on spiral galaxy in the background."[43]

"The image was made by combining data from the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3). The ACS exposures were taken April 12, 2010; the WFC3 data, April 4, 2010."[43]

GreensEdit

 
This is a visual astronomy image of IC 1396 in Cepheus using narrowband filters: sulfur is red, oxygen blue and hydrogen in green. Credit: Michal Zolnowski, Solaris in Cracow, Poland.
 
This is the most detailed picture of IC 1295 object ever taken. Credit: ESO.

At right is a visual astronomy image of IC 1396 using narrowband filters: sulfur is red, oxygen blue and hydrogen in green. The image was captured using a Ritchey Chretien 12.5" with a 2180 mm focal length.

"This intriguing picture from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 [at left] surrounding a dim and dying star. It is located about 3300 light-years away in the constellation of Scutum (The Shield). This is the most detailed picture of this object ever taken."[44] Three filters are used in this image: the blue (B), visual (V) in green, and red (R) optical filters.[44] IC 1295 is at RA 18 54 37.25, Dec 39.41", the image is 6.82 x 6.82 arcminutes.[44]

YellowsEdit

 
NGC 3132 in Vela is a striking example of a planetary nebula. Credit: The Hubble Heritage Team (STScI/AURA/NASA).
 
These are examples of the various colors of yellow. Credit: Badseed.
 
Complements of yellow have a dominant wavelength in the range 380 to 480 nm. The green lines show several possible pairs of complementary colors. Credit: .
 
The image is of a horse colored with yellow ochre. from Lascaux cave. Credit: Cro-Magnon peoples.
 
This shows a field of yellow rapeseed. Credit: Petr Kratochvil.
 
This photo of yellow and green auroras shows convincingly that yellow is a distinctive result of the auroral process. Credit: Belinda Witzenhausen.
 
This image captures an unusual aurora from Urengoi, Russia. Credit: Unknown.
 
This aurora image from Alaska shows distinctive yellow associated with the horizon. Credit: Unknown.
 
This is another aurora from Alaska containing yellow. Credit: Unknown.
 
This orange and yellow aurora occurred above Beaghmore Stone Circles. Credit: Martin McKenna.

"An abundance analysis of the yellow symbiotic system AG Draconis reveals it to be a metal-poor K-giant ([Fe/H]=-1.3) which is enriched in the heavy s-process elements. ... the other yellow symbiotic stars are probably low-metallicity objects as well."[45]

"NGC 3132 [imaged at right] is a striking example of a planetary nebula. This expanding cloud of gas, surrounding a dying star, is known to amateur astronomers in the southern hemisphere as the "Eight-Burst" or the "Southern Ring" Nebula."[46]

"The name "planetary nebula" refers only to the round shape that many of these objects show when examined through a small visual telescope. In reality, these nebulae have little or nothing to do with planets, but are instead huge shells of gas ejected by stars as they near the ends of their lifetimes. NGC 3132 is nearly half a light year in diameter, and at a distance of about 2000 light years is one of the nearer known planetary nebulae. The gases are expanding away from the central star at a speed of 9 miles per second."[46]

"This image, captured by NASA's Hubble Space Telescope, clearly shows two stars near the center of the nebula, a bright white one, and an adjacent, fainter companion to its upper right. (A third, unrelated star lies near the edge of the nebula.) The faint partner is actually the star that has ejected the nebula. This star is now smaller than our own Sun, but extremely hot. The flood of ultraviolet radiation from its surface makes the surrounding gases glow through fluorescence. The brighter star is in an earlier stage of stellar evolution, but in the future it will probably eject its own planetary nebula."[46]

"In the Heritage Team's rendition of the Hubble image, the colors were chosen to represent the temperature of the gases. Blue represents the hottest gas [the oxygen 500.9 nm line], which is confined to the inner region of the nebula. Red represents the coolest gas [hydrogen Hα line], at the outer edge. The Hubble image also reveals a host of filaments, including one long one that resembles a waistband, made out of dust particles which have condensed out of the expanding gases. The dust particles are rich in elements such as carbon. Eons from now, these particles may be incorporated into new stars and planets when they form from interstellar gas and dust. Our own Sun may eject a similar planetary nebula some 6 billion years from now."[46]

The yellow line, or band, used as an intermediate temperature is due to the overlap between the oxygen cyan line and the Hα line.

"To see day objects with most distinctness, I require a less concave lens by one degree than for seeing the stars best by night, the cause of which seems to be, that the bottom of the eye being illuminated by the day objects, and thereby rendered a light ground, obscures the fainter colours blue indigo and violet in the circle of dissipation, and therefore the best image of the object will be found in the focus of the bright yellow rays, and not in that of the mean refrangible ones, or the dark green, agreeable to Newton's remark, and consequently nearer the retina of a short-sighted person; but the parts of the retina surrounding the circle of dissipation of a star being in the dark, the fainter colours, blue, indigo, and violet, will have some share in forming the image, and consequently the focus will be shorter."[47] Bold added.

"The error due to color loses its disturbing effect because the photographic plate is not sensitive for the red and yellow rays, while the photographically active rays of shorter wave-length are well united by the objective."[48]

"The star brightness increase in 1964 was considerably different in yellow and blue rays. ... Extensive tables and graphs represent the mean photographic and photovisual curve of V1329 Cyg observed in Moscow and Odessa, brightness curves in blue and yellow rays, brightness increases, and brightness minima before and after an outburst."[49]

"The GE Reveal bulb is marketed as the bulb that is made to “specially filter out yellow rays that hide life's true colors.” This is accomplished by the use of neodymium in the glass."[50]

Def. the colour of gold or butter; the colour obtained by mixing green and red light, or by subtracting blue from white light is called yellow.

Def.

a bright yellow colour, resembling the metal gold

is called

gold.

Yellow, in the form of yellow ochre pigment made from clay, was one of the first colors used in prehistoric cave art. The cave of Lascaux has an image of a horse colored with yellow estimated to be 17,300 years old.

Shades of yellow contains a more diverse set of yellow or yellow-like colors.

Any doubt that a yellow aurora can occur should be put to rest with the image on the right.

The image on the left shows individual rays of radiation apparently impacting an upper atmospheric layer to produce a bead-like pattern.

The second image down on the left shows yellow of an aurora near the horizon with apparently the midnight Sun off to the left.

The third image on the left contains yellow aurora that is closer to true yellow.

The second image down on the right shows a yellow aurora following the skyline with an orange aurora above.

"On February 25th 2014 a violent X4.9-class solar flare erupted from a large sunspot group which had just rotated into view around the SE limb of the solar disk. The CME it unfurled was a massive full halo feature in the form of an expanding cloud of highly charged particles and plasma en route to the inner planets at a staggering velocity of over 2000km/sec. At this speed the CME would sweep across 93 million miles of space and impact planet Earth in only two days. However there was bad news as the source of this flare - and subsequent CME event - was located so close to the limb of the sun that the CME was very unlikely to impact Earth because it was located too far from the meridian and hence was not termed geoeffective which meant there was no chance of any Earth directed component at all. A few hours later a more detailed look by spaceweather scientists followed which offered some cautious optimism for in some of their forecasting models there was a slight chance that the CME could hit Earth a glancing blow with a possibility of minor geomagnetic storms on Feb 27th however the consensus was that the CME would probably miss entirely or if there was a hit then it wasn't expected to be significant."[51]

"The Bz is the secret to a good aurora show, this is [where] its at, the Bz (pronounced Bee Sub Zee) is a value indicating the tilt of the Interplanetary Magnetic Field or IMF. If the Bz is N then you can forget about a good show, even if the KP is good it won't make a difference, however if the Bz tilts S then the Earth and Sun's magnetic fields become aligned and in effect what you are doing is opening a gate way [...] allowing the highly charged solar particles to interact with the Earth's magnetosphere undisturbed - this open channel will manifest as a strong geomagnetic storm. The fact that it was - 20 got me extremely excited, this value meant the aurora was going to be strong and would be seen from far more southern latitudes than usual."[51]

RedsEdit

 
This is a red aurora borealis. Credit: Isarl.
 
A view of an all-red aurora is captured in Independence, Mo., on October 24, 2011. Credit: Tobias Billings.

"The nature of extremely red objects (EROs) remains an open question in understanding the faint galaxy population at z > 1."[52]

In wavelengths, red astronomy covers 620 - 750 nm.

Infrared or red radiation from a common household radiator or electric heater is an example of thermal radiation, as is the heat emitted by an operating incandescent light bulb. Thermal radiation is generated when energy from the movement of charged particles within atoms is converted to electromagnetic radiation.

Infrared (IR) light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometres (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz,[53] and includes most of the thermal radiation emitted by objects near room temperature. Infrared light is emitted or absorbed by molecules when they change their rotational-vibrational movements.

Far-red light is light at the extreme red end of the visible spectrum, between red and infra-red light. Usually regarded as the region between 710 and 850 nm wavelength, it is dimly visible to some [human] eyes.

On the right is an example of a red aurora borealis.

"A coronal mass ejection (CME) shot off the sun late in the evening of October 21 [2011] and hit Earth on October 24 at about 2 PM ET. The CME caused strong magnetic field fluctuations near Earth's surface – technically, this level of magnetic fluctuation rated a 7 out of 9 on what is called the "KP index" – that resulted in aurora that could be seen in the US as far south as Alabama. This image [on the left] was captured in Independence, Mo. Such completely red aurora are not as common as green aurora, however they can happen during strong solar activity and they occur a little more often at low latitudes such as where this was taken."[54]

"The strength, speed, and mass of this CME also pushed the boundary of Earth's magnetic fields – a boundary known as the magnetopause – from its normal position at about 40,000 miles away from Earth in to about 26,000 miles. This is the area where spacecraft in geosynchronous orbit reside, so these spacecraft were briefly orbiting outside of Earth's normal environment, traveling through material and magnetic fields far different from usual."[54]

InfraredsEdit

 
Infrared astronomy, especially from space, explores up a vast portion of the spectrum beyond the red end of visible light. Credit: IRAS / ISO / 2MASS / Spitzer.

The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves. Infrared rays can be emitted, fluoresced, or reflected by an astronomical object.

Def. electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation, having a wavelength between 700 nm and 1 mm is called infrared.

Def. [e]lectromagnetic radiation having a wavelength approximately between 1 micrometre and 1 millimetre; perceived as heat is called infrared radiation.

Astronomers typically divide the infrared spectrum as follows:[55]

Designation Abbreviation Wavelength
Near Infrared NIR (0.7–1) to 5 µm
Mid Infrared MIR 5 to (25–40) µm
Far Infrared FIR (25–40) to (200–350) µm.

These are the approximate ranges for photon energies of the infrared bands:

Division Name Wavelength Photon Energy
Near-infrared 0.75-1.4 µm 0.9-1.7 eV
Short-wavelength infrared 1.4-3 µm 0.4-0.9 eV
Mid-wavelength infrared 3-8 µm 150-400 meV
Long-wavelength infrared 8–15 µm 80-150 meV
Far infrared 15 - 1,000 µm 1.2-80 meV
Wavelength range
(micrometres)
Astronomical bands Telescopes
0.65 to 1.0 R and I bands All major optical telescopes
1.1 to 1.4 J band Most major optical telescopes and most dedicated infrared telescopes
1.5 to 1.8 H band Most major optical telescopes and most dedicated infrared telescopes
2.0 to 2.4 K band Most major optical telescopes and most dedicated infrared telescopes
3.0 to 4.0 L band Most dedicated infrared telescopes and some optical telescopes
4.6 to 5.0 M band Most dedicated infrared telescopes and some optical telescopes
7.5 to 14.5 N band Most dedicated infrared telescopes and some optical telescopes
17 to 25 Q band Some dedicated infrared telescopes and some optical telescopes
28 to 40 Z band Some dedicated infrared telescopes and some optical telescopes
330 to 370 Some dedicated infrared telescopes and some optical telescopes
450 submillimeter Submillimeter telescopes

The infrared band may be divided up “based on the response of various detectors:[56]

  • Near infrared: from 0.7 to 1.0  µm (from the approximate end of the response of the human eye to that of silicon).
  • Short-wave infrared: 1.0 to 3  µm (from the cut off of silicon to that of the MWIR atmospheric window. InGaAs covers to about 1.8  µm; the less sensitive lead salts cover this region.
  • Mid-wave infrared: 3 to 5  µm (defined by the atmospheric window and covered by indium antimonide [InSb] and HgCdTe and partially by lead selenide [PbSe]).
  • Long-wave infrared: 8 to 12, or 7 to 14  µm: the atmospheric window (Covered by HgCdTe and microbolometers).
  • Very-long wave infrared (VLWIR): 12 to about 30  µm, covered by doped silicon.

A commonly used sub-division scheme is:[57]

Division Name Abbreviation Wavelength Characteristics
Near-infrared NIR, IR-A DIN 0.75-1.4 µm Defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.
Short-wavelength infrared SWIR, IR-B DIN 1.4-3 µm Water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications.
Mid-wavelength infrared MWIR, IR-C DIN. Also called intermediate infrared (IIR) 3-8 µm In guided missile technology the 3-5 µm portion of this band is the atmospheric window in which the homing heads of passive IR 'heat seeking' missiles are designed to work, homing on to the Infrared signature of the target aircraft, typically the jet engine exhaust plume
Long-wavelength infrared LWIR, IR-C DIN 8–15 µm This is the "thermal imaging" region, in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and requiring no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. This region is also called the "thermal infrared."
Far infrared FIR 15 - 1,000 µm (see also far-infrared laser).

NIR and SWIR is sometimes called "reflected infrared" while MWIR and LWIR is sometimes referred to as "thermal infrared." Due to the nature of the blackbody radiation curves, typical 'hot' objects, such as exhaust pipes, often appear brighter in the MW compared to the same object viewed in the LW.

SubmillimetersEdit

"On the whole the emission strength is low in the submillimeter for astronomical objects."[58]

RadarsEdit

 
This image is of asteroid 2012 LZ1 by the Arecibo Observatory in Puerto Rico using the Arecibo Planetary Radar. Credit: Arecibo Observatory.

Radar astronomy is used to detect and study astronomical objects that reflect radio rays.

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."[59]

Plasma objectsEdit

 
Representation of upper-atmospheric lightning and electrical-discharge phenomena are displayed. Credit: .
 
The surface of a MEMS device is cleaned with bright, blue oxygen plasma in a plasma etcher to rid it of carbon contaminants. (100mTorr, 50W RF) Credit: .
 
This image of the Northern Lights shows the very rare blue light. Credit: Varjisakka.
 
2 kW Hall thruster is in operation as part of the Hall Thruster Experiment at the Princeton Plasma Physics Laboratory. Credit: Dstaack.
 
This is an image of planetary nebula NGC 7662, the Blue Snowball, in Andromeda. Credit: Adam Block, Caelum Observatory.
 
This is a xenon 6 kW Hall thruster in operation at the NASA Jet Propulsion Laboratory. Credit: NASA/JPL-Caltech.
 
This is a color composite image of NGC 7662. Credit: Judy Schmidt.

"Plasma is the fourth state of matter, consisting of electrons, ions and neutral atoms, usually at temperatures above 104 degrees Kelvin."[60]

[P]lasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms (reduce or increase the number of electrons in them), thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions.[61]

For plasma to exist, ionization is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e., response to magnetic fields and high electrical conductivity). The degree of ionization, α is defined as α = ni/(ni + na) where ni is the number density of ions and na is the number density of neutral atoms. The electron density is related to this by the average charge state <Z> of the ions through ne = <Z> ni where ne is the number density of electrons.

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).[62] 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 [63] and appear to be "an upward moving luminous phenomenon closely related to blue jets."[64] They appear to be shorter and brighter than blue jets, reaching altitudes of only up to 20 km.[65]

Blue starters appear to be blue jets that never quite make it".[66]

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.

"When magnetic fields "reconnect" in a turbulent magnetohydrodynamic (MHD) plasma, electric fields are generated in which particles can be accelerated (Matthaeus et al., 1984; Sorrell, 1984)."[18]

In spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the ions in the plume. Hall thrusters are sometimes referred to as Hall effect thrusters or Hall current thrusters. Hall thrusters are often regarded as a moderate specific impulse (1,600 s) space propulsion technology. Hall thrusters operate on a variety of propellants, the most common being xenon. Other propellants of interest include krypton, argon, bismuth, iodine, magnesium, and zinc.

At left are two images of the plasma associated with and a part of NGC 7662. The color of the nebula is very blue-green where the dominant light source is the 500.7 nm oxygen emission.

The second image is from the Hubble Space Telescope through three filters: F502N (blue), F555W (green), and F658N (red). The object is a planetary nebula (NGC 7662). A small star in the center has produced the nebula.

Gaseous objectsEdit

 
Praia da Ursa, Sintra, Portugal is shown as part of a blue hour seascape seen in wide angle. Credit: Rnbc.
 
The Colosseum is shown during the blue hour. Credit: Diliff.
 
Blue hour in Paris is shown around the Eiffel Tower. Credit: Getfunky Paris.
 
Brandenburg Gate is shown in Berlin during the blue hour. Credit: Ondřej Žváček (Ondřej Žváček).
 
The illuminated mining lamp memorial in Moers is shown during the blue hour. Credit: kaʁstn.
 
This is an image in real color of the Witch's Broom, a portion of the Veil Nebula. Credit: NASA APOD/Martin Pugh.

Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H ions, which absorb visible light easily.[67] Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H ions.[68][69] The photosphere has a particle density of ~1023 m−3 (this is about 0.37% of the particle number per volume of Earth's atmosphere at sea level; however, photosphere particles are electrons and protons, so the average particle in air is 58 times as heavy).

"Positrons entering a gaseous medium at [0.6 to 4.5 MeV] are quickly slowed by ionizing collisions with neutral atoms and by long-range Coulomb interactions with any ionized component."[70]

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.

"In the western part of the Veil [Nebula] lies another seasonal apparition, the Witch’s Broom, [a] portion of the same remnant, this time resembling, you guessed it, a witch’s broom, with the sweeping end of the broom facing bottom right of the image [at right.] [The Broom is imaged] with narrow band filters[. The] glowing filaments are like long ripples in a sheet seen almost edge-on, remarkably well separated into atomic hydrogen (red) and oxygen (blue-green) gas".[71]

Liquid objectsEdit

 
This is a detailed, photo-like view of Earth based largely on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Credit: Robert Simmon and Marit Jentoft-Nilsen, NASA.
 
Cyan is the color of clear water over a sandy beach. Credit: visualpanic from Barcelona.
 
The image shows a blue sky, white clouds over a blue-green ocean on Earth. Credit: SKYLIGHTS.

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."[72]

Cyan is the color of clear water over a sandy beach, as here at Cala Macaralleta, Menorca.

Rocky objectsEdit

 
This Sin-Kamen (Blue Rock) near Lake Pleshcheyevo used to be a Meryan shrine Credit: Viktorianec.
 
This is a blue rock, probably various copper minerals, from the Berkeley hills near San Francisco, California. Credit: Looie496.
 
This is an approximately natural color picture of the asteroid 243 Ida on August 28, 1993. Credit: NASA/JPL.

"Even in small solids and dust grains, energy deposition from 26Al β-decay, for example, injects 0.355 W kg-1 of heat. This is sufficient to result in melting signatures, which have been used to study condensation sequences of solids in the early solar system".[73]

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[74]).

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.[75]

"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."[76]

At second right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."[77]

"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."[78]

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock.[79] Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.[79] [...] Slate is frequently grey in color, especially when seen, en masse, covering roofs. However, slate occurs in a variety of colors even from a single locality; for example, slate from North Wales can be found in many shades of grey, from pale to dark, and may also be purple, green or cyan.

HydrogensEdit

Main sources: Chemicals/Hydrogens and Hydrogens
 
The spectrum shows the lines in the visible due to emission from elemental hydrogen. Credit:Teravolt.
 
IC 5148 is a beautiful planetary nebula located some 3000 light-years away in the constellation of Grus (The Crane). Credit: ESO.

The hydrogen H-beta line (Hβ) has a wavelength of 486.1 nm.

On July 1, 1957, "Following the intense auroral display of the previous night, ... The variation in Hβ emission ... shows quite clearly that the sudden transition from an [auroral] arc to rays coincides with a decrease in the intensity of the hydrogen emission and an inversion of the polarity of the magnetic disturbance."[80]

"IC 5148 is a beautiful planetary nebula located some 3000 light-years away in the constellation of Grus (The Crane). The nebula has a diameter of a couple of light-years, and it is still growing at over 50 kilometres per second — one of the fastest expanding planetary nebulae known. The term “planetary nebula” arose in the 19th century, when the first observations of such objects — through the small telescopes available at the time — looked somewhat like giant planets. However, the true nature of planetary nebulae is quite different."[81]

"The ESO Faint Object Spectrograph and Camera (EFOSC2) on the New Technology Telescope at La Silla gives a somewhat more elegant view of this object. Rather than looking like a spare tyre, the nebula resembles ethereal blossom with layered petals."[81]

The color bands and filters used for the IC 5158 image are blue (optical), Hβ (blue, optical), visual (V, green optical), yellow (R, optical), and Hα (red, optical).[81]

The purple coloration results from a combination of blue and red.

MeteoritesEdit

Main sources: Rocks/Meteorites and Meteorites
 
This image shows the lunar meteorite Allan Hills 81005. Credit: NASA.
 
NWA 6963 is an igneous Martian shergottite meteorite found in September 2011 in Morocco. Credit: Steve Jurvetson.

Cosmic ray exposure history established with noble gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years.

Imaged at lower right is an igneous Martian shergottite meteorite. "The perimeter exhibits a fusion crust from the heat of entry into the Earth’s atmosphere. It is a fresh sample of NWA 6963, an igneous Martian shergottite meteorite found in September 2011 in Morocco. Meteorites are often labeled NWA for North West Africa, not because they land there more often, but because they are easy to spot as peculiar objects in the desert sands. From the geochemistry and presence of various isotopes, the origin and transit time is deduced. The 99 meteorites from Mars exhibit precise elemental and isotopic compositions similar to rocks and atmosphere gases analyzed by spacecraft on Mars, starting with the Viking lander in 1976. Compared to other meteorites, the Martians have younger formation ages, unique oxygen isotopic composition (consistent for Mars and not for Earth), and the presence of aqueous weathering products. A trapped gas analysis concluded that their origin was Mars quite recently, in the year 2000."[82]

"The formation ages of meteorites often come from their cosmic-ray exposure (CRE), measured from the nuclear products of interactions of the meteorite in space with energetic cosmic ray particles. This one is particularly young, having crystallized only 180 million years ago, suggesting that volcanic activity was still present on Mars at that time. Volcanic flows are the youngest part of a planet, and this one happened to be hit by a meteor impact, ejecting" it from the youthful Mars.[82]

SunEdit

Main sources: Stars/Sun and Sun (star)

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.[83]

Very occasionally, the amount of blue light is sufficient to be visible as a "blue flash".[84]

EarthEdit

Main source: Draft:Earth
 
This is the famous Blue Marble image of Earth taken by Apollo 17. Credit: NASA. Photo taken by either Harrison Schmitt or Ron Evans (of the Apollo 17 crew).

With respect to the rocky-object Draft:Earth, between the surface and various altitudes there is an electric field induced by the ionosphere. It changes with altitude from about 150 volts per meter at the suface to lower values at higher altitude. In fair weather, it is relatively constant, in turbulent weather it is accompanied by ions. At greater altitude these chemical species continue to increase in concentration. To dissipate the accumulation of greater charge differential between the surface and the ionosphere, the gases between suffer breakdown (ionization) that permits lightning to be either a draw of negative charge, usually electrons, upward from the surface or a transfer of positive charge to the ground.

The 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 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.

MoonEdit

Science about the apparent rocky object in close proximity to the Draft:Earth has been accumulating perhaps since the beginning of oral traditions and written records. A number of intelligent species currently or formerly extant on Earth may have made such traditions and records.

AsteroidsEdit

Def. a "naturally occurring solid object, [which is] smaller than a planet[85] and is not a comet,[86] that orbits a star"[87] is called an asteroid.

Usage notes

"The term "asteroid" has never been precisely defined. It was coined for objects which looked like stars in a telescope but moved like planets. These were known from the asteroid belt between Mars and Jupiter, and were later found co-orbiting with Jupiter (Trojan asteroids) and within the orbit of Mars. They were naturally distinguished from comets, which did not look at all starlike. Starting in the 1970s, small non-cometary bodies were found outside the orbit of Jupiter, and usage became divided as to whether to call these "asteroids" as well. Some astronomers restrict the term "asteroid" to rocky or rocky-icy bodies with orbits up to Jupiter. They may retain the term planetoid for all small bodies, and thus tend to use it for icy or rocky-icy bodies beyond Jupiter, or may use dedicated words such as centaurs, Kuiper belt objects, transneptunian objects, etc. for the latter. Other astronomers use "asteroid" for all non-cometary bodies smaller than a planet, even large ones such as Sedna and (occasionally) Pluto. However, the distinction between asteroid and comet is an artificial one; many outer "asteroids" would become comets if they ventured nearer the Sun. The official terminology since 2006 has been small Solar System body for any body that orbits the Sun directly and whose shape is not dominated by gravity."[85]

A asteroidsEdit

Spectra "of several related asteroid classes (types A, R, and V) were also analyzed for comparison to various S-subtypes."[88]

"Observing 246 Asporina and 289 Nenetta, [6] were the first to identify A-type asteroids as nearly pure olivine assemblages based on their spectral characteristics. These asteroids display a single broad absorption feature centered at 1.06 μm (Band I) without any significant pyroxene feature at ~2.0 μm (Band II)."[89]

Only "a handful of A-type objects were discovered during the taxonomic surveys, assuming that all A-type asteroids are olivine-rich. The study of A-type asteroids may help solve the “missing mantle problem” in the asteroid belt."[89]

Carbonaceous asteroidsEdit

C-type asteroids are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids,[90] and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except D-types and others common only at the extreme outer edge of the asteroid belt. Their spectra contain moderately strong ultraviolet absorption at wavelengths below about 0.4 μm to 0.5 μm, while at longer wavelengths they are largely featureless but slightly reddish. The so-called "water" absorption feature around 3 μm, which can be an indication of water content in minerals is also present.

G asteroidsEdit

"G-type asteroids are a relatively uncommon type of carbonaceous asteroid. The most notable asteroid in this class is 1 Draft:Ceres. Generally similar to the C-type objects, but containing a strong ultraviolet absorption feature below 0.5 μm.

K asteroidsEdit

"Bell (1988) distinguished a new class (K-type) from previous members of the S-class and interpreted these objects as composed of material analogous to the undifferentiated CO3 ro CV3 carbonaceous chondrites."[88]

M asteroidsEdit

"Exposure of compositionally distinct internal layers from within parent planetesimals may be an important source of the diversity within the S-population and is presumably the source of the M- and A-type."[88]

"M-class [...] contains both metallic objects [...] 216 Kleopatra and [...] 16 Psyche".[91]

R asteroidsEdit

"A-type asteroids are a relatively rare taxonomic class with no more than 17 known objects [1,2,3]. They were first identified as a separate group of R-type asteroids based on broadband spectrophotometry by [4], and were later classified based on ECAS data by Tholen (1984) [1]."[89]

V asteroidsEdit

 
As NASA's Dawn spacecraft takes off for its next destination, this mosaic synthesizes some of the best views the spacecraft had of the giant asteroid Vesta. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA.
 
Location and structure of the Vesta family are depicted. Credit: Deuar.

In the full image of Vesta at right, the rocky-object appears to have suffered from meteor damage.

Vesta, minor-planet designation 4 Vesta, is one of the largest asteroids in the Solar System. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.[92][93]

"V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta."[94]

The Vestian asteroids consist "of 4 Vesta, the second-most-massive of all asteroids (mean diameter of 530 km), and many small asteroids below 10 km diameter. The brightest of these, 1929 Kollaa and 2045 Peking, have an absolute magnitude of 12.2, which would give them a radius of about 7.5 km assuming the same high albedo as 4 Vesta."[95]

"A HCM numerical analysis (by Zappala 1995) determined a large group of 'core' family members, whose proper orbital elements lie in the approximate ranges"[95]

ap ep ip
min 2.26 AU 0.075 5.6°
max 2.48 AU 0.122 7.9°

"This gives the approximate boundaries of the family. At the present epoch, the range of  osculating orbital elements of these core members is"[95]

a e i
min 2.26 AU 0.035 5.0°
max 2.48 AU 0.162 8.3°

"The Zappala 1995 analysis[96] found 235 core members. A search of a recent proper-element database (AstDys) for 96944 minor planets in 2005 yielded 6051 objects (about 6% of the total) lying within the Vesta-family region as per the first table above."[95]

Apollo asteroidsEdit

 
This a diagram showing the Apollo asteroids, compared to the orbits of the terrestrial planets of the Solar System.
  Draft:Mars (M)
  Draft:Venus (V)   Draft:Mercury (H)
  Sun
  Apollo asteroids
  Draft:Earth (E)
Credit: AndrewBuck.

Note that sizes and distances of bodies and orbits are not to scale in the image on the right.

As of 2015, the Apollo asteroid group includes a total of 6,923 known objects of which 991 are numbered (JPL SBDB).

CentaursEdit

Def. an "icy planetoid that orbits the Sun between Draft:Jupiter and Draft:Neptune"[97] is called a Centaur.

"The recent investigation of the orbital distribution of Centaurs (Emel’yanenko et al., 2005) showed that there are two dynamically distinct classes of Centaurs, a dominant group with semimajor axes a > 60 AU and a minority group with a < 60 AU."[98] "[T]he intrinsic number of such objects is roughly an order of magnitude greater than that for a<60 AU".[98]

CometsEdit

 
This image shows Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.
 
This image shows Comet 67P/Churyumov-Gerasimenko rotated around a vertical axis from the right. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.

The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.

The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.

Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.

Comet BorrellyEdit

 
This image reveals dust being ejected from the nucleus of comet Borrelly. Credit: NASA/JPL.
 
Comet Borrelly is imaged by Deep Space 1 revealing no surface ice. Credit: NASA/JPL.

"A typical comet nucleus has an albedo of 0.04.[99]

"This image, taken by Deep Space 1 on September 22, 2001, has been enhanced to reveal dust being ejected from the nucleus of comet Borrelly. As a result, the nucleus, which is about eight kilometers (about five miles) long, is bright white in the image. The main dust jet is directed towards the bottom left of the frame, around 35 degrees away from the comet-Sun line. The jet emerges as actually comprised of at least three smaller features. This active region as a whole is at least three kilometers (less than two miles) long."[100]

"Another, smaller, jet feature is seen on the tip of the nucleus on the lower right-hand limb. Dust also seems to be ejected from there into the night-side hemisphere, probably from the dayside hemisphere. The expansion of the gas and dust mixture into the vacuum of space has swept some material around the body of the nucleus so that it appears above the night-side hemisphere. The night-side of the nucleus could not be seen, of course."[100]

"The line between day and night on the comet is towards the upper right. This representation shows a faint ring of brightness separated from the terminator by a dark, unlit area. It is possible that this is a crater rim, seen in grazing illumination, which is just about to cross into darkness as the comet rotates. The direction to the Sun is directly downwards."[100]

On the left is a close-up picture of comet Borelly. The right portion is a topographic relief map of the cometary nucleus.

"Comets are sometimes described as "dirty snowballs," but a close flyby of one by NASA's Deep Space 1 spacecraft last fall detected no frozen water on its surface."[101]

"The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice."[102]

"We know the ice is there. It's just well-hidden. Either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice."[102]

"The Deep Space 1 science team released pictures and other initial findings days after the spacecraft flew within 2,171 kilometers (1,349 miles) of the comet's solid nucleus on September 22, 2001."[101]

"Comet Borrelly is in the inner solar system right now, and it's hot, between 26 and 71 degrees Celsius (80 and 161 degrees Fahrenheit), so any water ice on the surface would change quickly to a gas. As the components evaporate, they leave behind a crust, like the crust left behind by dirty snow."[103]

"It seems to be covered in this dark material, which has been loosely connected with biological material. This suggests that comets might be a transport mechanism for bringing the building blocks of life to Earth."[103]

"It's remarkable how much information Deep Space 1 was able to gather at the comet, particularly given that this was a bonus assignment for the probe."[104]

Comet 67P/Churyumov-GerasimenkoEdit

 
This is an image of the nucleus of Comet 67P/Churyumov-Gerasimenko by Rosetta. Credit: ESA Rosetta Mission.{{free media}}
 
Single frame Rosetta spacecrast NAVCAM image of Comet 67P/C-G was taken on 6 March from a distance of 82.9 km to the comet. Credit: ESA/Rosetta/NAVCAM.{{free media}}
 
Images taken by the Rosetta navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/NAVCAM.{{free media}}
 
Four-image montage comprises images taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. Credit: ESA/Rosetta/NAVCAM.{{free media}}
 
Image is taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G Credit: ESA/Rosetta/NAVCAM.{{free media}}

"The short period comets have orbital periods <20 years and low inclination. Their orbits are controlled by Jupiter and thus they are also called Jupiter Family comets. [...]  Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive planet.  The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun."[105]

Perihleion distance in AU = 1.243, eccentricity = 0.641, inclination = 7.0, and orbital period in years = 2.745.[106]

Comet Schwassmann-Wachmann I (P/SW-1)Edit

 
This is an infrared image of the periodic comet Schwassmann-Wachmann I (P/SW-1) in a nearly circular orbit just outside that of Jupiter. Credit: NASA/JPL-Caltech/D. Cruikshank (NASA Ames) & J. Stansberry (University of Arizona.

"NASA's new Spitzer Space Telescope has captured [the image right] of an unusual comet that experiences frequent outbursts, which produce abrupt changes in brightness. Periodic comet Schwassmann-Wachmann I (P/SW-1) has a nearly circular orbit just outside that of Jupiter, with an orbital period of 14.9 years. It is thought that the outbursts arise from the build-up of internal gas pressure as the heat of the Sun slowly evaporates frozen carbon dioxide and carbon monoxide beneath the blackened crust of the comet nucleus. When the internal pressure exceeds the strength of the overlying crust, a rupture occurs, and a burst of gas and dust fragments is ejected into space at speeds of 450 miles per hour (200 meters per second)."[107]

"This 24-micron image of P/SW-1 was obtained with Spitzer's multiband imaging photometer. The image shows thermal infrared emission from the dusty coma and tail of the comet. The nucleus of the comet is about 18 miles (30 kilometers) in diameter and is too small to be resolved by Spitzer. The micron-sized dust grains in the coma and tail stream out away from the Sun. The dust and gas comprising the comet's nucleus is part of the same primordial materials from which the Sun and planets were formed billions of years ago. The complex carbon-rich molecules they contain may have provided some of the raw materials from which life originated on Earth."[107]

"Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the solar system."[107]

Kuiper belt objectsEdit

"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."[108]

"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."[109]

Circumstellar cloudsEdit

 
Astronomers use polarized light to map the hypergiant star VY Canis Majoris. Credit: NASA, ESA, and R. Humphreys (University of Minnesota).
 
This is a visible light image of VY Canis Majoris. Credit: NASA, ESA, and N. Smith (University of Arizona).

Def. an interstellar-like cloud apparently surrounding or in orbit around a star is called a circumstellar cloud.

"VY Canis Majoris [a red hypergiant star is] an irregular pulsating variable [that] lies about 5,000 light-years away in the constellation Canis Major."[110]

"Although VY Can is about half a million times as luminous as the Sun, much of its visible light is absorbed by a large, asymmetric cloud of dust particles that has been ejected from the star in various outbursts over the past 1,000 years or so. The infrared emission from this dust cloud makes VY Can one of the brightest objects in the sky at wavelengths of 5–20 microns."[110]

"In 2007, a team of astronomers using the 10-meter radio dish on Mount Graham, in Arizona, found that VY Can's extended circumstellar cloud is a prolific molecule-making factory. Among the radio emissions identified were those of hydrogen cyanide (HCN), silicon monoxide (SiO), sodium chloride (NaCl) and a molecule, phosphorus nitride (PN), in which a phosphorus atom and a nitrogen atom are bound together. Phosphorus-bearing molecules are of particular interest to astrobiologists because phosphorus is relatively rare in the universe, yet it is a key ingredient in molecules that are central to life as we know it, including the nuclei acids DNA and RNA and the energy-storage molecule, ATP. "[110]

"Material ejected by the star is visible in this 2004 image [on the top right] captured by the Hubble Space Telescope's Advanced Camera for Surveys, using polarizing filters."[110]

For comparison, the second image down on the right is captured using visuals.

Luminous blue variablesEdit

Luminous blue variables, also known as S Doradus variables, are very bright, blue, hypergiant variable stars named after S Doradus, the brightest star of the Large Magellanic Cloud. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial mass loss events (e.g. Eta Carinae, P Cygni). They are extraordinarily rare. The General Catalogue of Variable Stars only lists 20 objects as SDor.[111]

LBVs can shine millions of times brighter than the Sun and, with masses up to 150 times that of the Sun, approaching the theoretical upper limit for stellar mass, making them among the most luminous, hottest, and most energy-releasing stars in the universe. If they were any larger, their gravity would be insufficient to balance their radiation pressure and they would blow away the excess mass through stellar wind. As they are, they barely maintain hydrostatic equilibrium because their stellar wind constantly ejects matter, decreasing the mass of the star. For this reason, there are usually nebulae around such stars created by these outbursts; Eta Carinae is the nearest and best-studied example. Because of their large mass and high luminosity, their lifetime is very short — only a few million years.

HypothesesEdit

Main source: Hypotheses
  1. Not all astronomical objects are detectable by Draft:radiation astronomy.

See alsoEdit

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