Radiation astronomy/Blues

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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.[1] Blue main sequence stars, that are metal poor, ([Fe/H] ≤ -1.0) are most likely not analogous to blue stragglers.[1]

"[G]round-based UV [and blue astronomy] is a powerful facility for [the] study of [the] chemical evolution of [the] early Galaxy."[2] The UV and B astronomy are over the wavelength range 355.0–500.0 nm.[2]

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,[3] 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.


Blue is between violet and green in the spectrum of visible light. Credit: Gringer.

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.

Planetary sciences[edit]

The Earth's shadow at sunrise is seen over a horizon where the sea meets the sky, looking west from Twin Peaks, San Francisco. Note: the lowest blue-grey area is not the sky but the surface of the Pacific Ocean. Credit: .
Earth's shadow and Belt of Venus at sunset, looking east from the Marin Headlands just north of San Francisco. (Note: there is a thin greyish cloud layer partially obscuring the horizon in this image.) Credit: .

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.[4][5] 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.[4][5]

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.[4]



"A solar tracker is a device that orients a payload toward the sun.


"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.



These are various shades of blue. Credit: Booyabazooka.

Blue is the colour of the clear sky and the deep sea.[7]

"De la couleur du ciel sans nuages, de l'azur"[8]

Blue minerals[edit]




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.





Lazurite is a deep blue tectosilicate. Credit: .


Blueschist facies[edit]


Metamorphic facies blanc.svg

T (°C)

A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures.[9] 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).[9] Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in geological history of the area.[9] The boundaries between facies (and corresponding areas on the temperature v. pressure graph), are wide, because they are gradational and approximate.[9] 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.[9]



This is a specimen of glaucophane with fuchsite. Credit: .




Hauyne, haüyne or hauynite [occurs] in Vesuvian lavas in Monte Somma, Italy,[11] ... It is a tectosilicate mineral with sulfate, with endmember formula Na3Ca(Si3Al3)O12(SO4).[12] ... It is a feldspathoid and a member of the sodalite group.[13][14] Haüyne occurs in phonolites and related leucite- or nepheline-rich, silica-poor, igneous rocks; less commonly in nepheline-free extrusives[15][13][14][16] and metamorphic rocks (marble).[13]

Water ice[edit]


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.[17] Ice is blue for the same reason water is blue: it is a result of an overtone of an oxygen-hydrogen (O-H) bond stretch in water which absorbs light at the red end of the visible spectrum.[18]

Theoretical blue-ray astronomy[edit]

"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".[19]


Bhagwan Ayodhyapati Siyavara Shri Ramachandra is shown. Credit: Redtigerxyz.





Rama imaged at left is the Daśāvatāra seventh avatar of the god Vishnu in Hinduism,[21] 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. [22] The Hindi word parivar translates as "family." [23]


This image shows a beam of accelerated ions (perhaps protons or deuterons) escaping the accelerator and ionizing the surrounding air causing a blue glow. Credit: Lawrence Berkely National Laboratory.
This image shows the blue glow generated by the synchrotron radiation from M87's Energetic Jet. Credit: Hubble Space Telescope.
The image shows the blue glow given off by the synchrotron beam from the National Synchrotron Light Source. Credit: NSLS, Brookhaven National Laboratory.

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.




A synchrotron model for the continuum spectrum of the Crab Nebula fits the radiation given off.[25]


"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."[26] 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).






Conversion of units over the Pioneer blue (B) bandpass is[27]

For example,

NCP NEP and NGP [27]


SCP SEP and SGP [27]


"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."[28]

Meteor showers[edit]

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].[29] The average pre-atmospheric velocity is 59.9 km/s.[29]


Of 225 Geminids observed in 1990 some 38 were blue in color, with one yellow-blue and one blue-green [cyan].[29] The average pre-atmospheric velocity is 36.2 km/s.[29]

Cosmic rays[edit]

"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."[30]

"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."[30]






"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."[32]

"[T]he lithium has a fragile nucleus which is destroyed by proton fusion when the temperature reaches 2 106 K."[32]

"[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."[32]

These well-known metal deficient stars have "high dispersion spectra in the blue wavelength range".[32]

"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."[32]

"[T]he lithium rich stars are not statistically younger than the lithium poor stars."[32]


"[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."[33]

"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."[33]


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."[34]


Supernova SN 1987A is one of the brightest stellar explosions since the invention of the telescope more than 400 years ago.[35] Credit: ESA/Hubble & NASA.

"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."[36]

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.[37]

Four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak -69° 202, a blue supergiant.[38] 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.[36]

Gamma rays[edit]

"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."[39]


This is a visual image of Abell 370. Credit: NASA, ESA, the Hubble SM4 ERO Team and ST-ECF.

"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."[40]

"[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."[41]


Cherenkov radiation glows in the core of the Advanced Test Reactor. Credit: Matt Howard.


Plasma objects[edit]

Representation of upper-atmospheric lightning and electrical-discharge phenomena are displayed. Credit: .


"Blue starters were discovered on video from a night time research flight around thunderstorms [43] and appear to be "an upward moving luminous phenomenon closely related to blue jets."[44] They appear to be shorter and brighter than blue jets, reaching altitudes of only up to 20 km.[45]

Blue starters appear to be blue jets that never quite make it".[46]



Gaseous objects[edit]

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.


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.

Liquid objects[edit]




Rocky objects[edit]









Helium II does have an emission line in the blue at 469 nm.













This spectrograph shows the visual spectral lines of lithium. Credit: T c951.


This image shows the emission lines for beryllium. Absorption occurs by subtraction of these lines from the continuum. Credit: Penyulap.

The emission and absorption spectra for beryllium contain lines in the blue.


This image shows the emission lines for boron and their approximate locations in the visible spectrum. Absorption lines occur at the same locations but with subtraction of light from the continuum. Credit: Penyulap.

The emission and absorption spectra for boron contain lines on the border between violet and blue.


The spectrum shows the lines in the visible due to emission from elemental carbon. Credit:Teravolt.

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.[54]


The spectrum shows the lines in the visible due to emission from elemental nitrogen. Credit:Kurgus.

Nitrogen has two emission lines that occur in plasmas at 455.368 and 455.545 nm from N VII.[54]

There is an "(0,2) vibrational component of the B-x electronic transition of N2(+) at 470.9 nm."[55]


The spectrum shows the lines in the visible due to emission from elemental oxygen. Credit:Teravolt.

The spectrum above shows the lines in the visible due to emission from elemental oxygen.


This diagram contains the emission and absorption lines for the element fluorine. Credit: Alex Petty.

The emission and absorption spectra of fluorine contains at least eight lines or bands from the cyan to the ultraviolet.[56]


This image shows the emission lines for atomic neon. Absorption lines occur at the same locations by subtraction of light from the continuum. Credit: Teravolt.

Like fluorine, neon has at least fourteen emission and absorption lines or bands from the cyan to the violet.[57]


Argon has an emission line that occurs in an electron cyclotron resonance (ECR) heated plasmas: 473.591 nm from Ar II.[54]


Titanium has two emission lines at 456.3757 and 457.1971 nm from Ti II.[58]


Chromium has two emission lines at 455.8650 and 458.8199 nm from Cr II.[58]


Iron has one emission line at 458.3837 nm from Fe II.[58]


An example of common occurring brownish hibonite. Credit: .

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.[59] [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."[60] "[T]he oxidation of minor elements in metallic alloys in the early solar system" is indicated to possess at instances a blue surface layer.[60]




"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."[62]


This view of a rock called "Block Island" shows the largest meteorite yet found on Mars. Credit: NASA/JPL-Caltech/Cornell University.

"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."[63]

"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."[63]



Very occasionally, the amount of blue light is sufficient to be visible as a "blue flash".[65]


The color image shown here at right was generated by combining the mosaics taken through the MESSENGER WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.




This real-color image of Venus is processed from imaging through the clear and blue filters on Mariner 10. Credit: NASA or Ricardo Nunes.

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.


The Earth has a blue halo when seen from space. Credit: .
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).

"Earth is a blue planet"[67].

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.



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.







This Mars rock reveals a bluish-gray interior to Mars Science Laboratory. Credit: NASA/JPL-Caltech/MSSS/ASU.
This natural color image is from NASA's Curiosity rover before it aimed two different instruments to study the rock known as "Jake Matijevic". Credit: NASA/JPL-Caltech/MSSS.
This is a color image made 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. Credit: NASA/JPL/Texas A&M/Cornell.
This is a natural color image by the HiRISE camera on the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.
This image shows the eastern (west-facing) side of an impact crater in the mid-latitudes of the Northern hemisphere. Credit: NASA/JPL/University of Arizona.
This image shows part of the floor of Rabe Crater, a large (108 kilometre diameter) impact crater in the Southern highlands of Mars. Credit: NASA/JPL/University of Arizona.
Gullies, exposed bedrock and deposits in an impact crater on Mars are photographed by the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.
Dunes of sand-sized materials have been trapped on the floors of many Martian craters. Credit: NASA/JPL-Caltech/University of Arizona.
This view of layered rocks on the floor of McLaughlin Crater shows sedimentary rocks that contain spectroscopic evidence for minerals formed through interaction with water. Credit: NASA/JPL-Caltech/Univ. of Arizona.
The HiRISE image does not show the entire crater. Credit: NASA/JPL/University of Arizona.


"[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."[74] Other bluish rocks can just be seen. Curiosity removed the Martian dust from "Jake Matijevic" before photographing.




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."[76]





The image at third left "shows part of the floor of Rabe Crater, a large (108 kilometre diameter) impact crater in the Southern highlands".[77]



The fourth image at right shows "pristine gullies, some with bright deposits, and perhaps very recent."[78]

"In addition, there is exposed bedrock, which at HiRISE resolution, we can pick out fine details. Observations like this can also help gully modeling."[78]

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."[79]


The fifth image at right shows layered rocks on the floor of McLaughlin Crater.[80]

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."[80]


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.



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 belt,[81] and its diameter of 544 kilometres (338 mi) is slightly larger than that of 4 Vesta. It is however 10–30% less massive than Vesta,[82] placing it third among the asteroids.





In addition to the usually cyan color of the plasma around the comet nucleus is a blue ion tail leading away to the right.









The passage of time is accelerated by a factor of 600,000.


This Galileo spacecraft image shows the approximate natural color appearance of Europa. Credit: NASA/JPL/DLR.








The image shows Saturn's northern hemisphere from the Cassini spacecraft with Mimas in front. Credit: NASA/JPL/Space Science Institute.

In the image at right, "Mimas drifts along in its orbit against the azure backdrop of Saturn's northern latitudes in this true color view from NASA's Cassini spacecraft. The long, dark lines on the atmosphere are shadows cast by the planet's rings."[87]












This image of the south polar region of Titan shows a depression in the blue and orange haze layers. Credit: Cassini Imaging Team, NASA/JPL-Caltech/Space Science Institute.

At right is an image of the blue haze layer near the south polar region of Titan. "The moon's high altitude haze layer appears blue here whereas the main atmospheric haze is orange. The difference in color could be due to particle size of the haze. The blue haze likely consists of smaller particles than the orange haze."[90]

"The depressed or attenuated layer appears in the transition area between the orange and blue hazes about a third of the way in from the left edge of the narrow-angle image. The moon's south pole is in the upper right of this image."[90]

"The southern pole of Titan is going into darkness as the sun advances towards the north with each passing day. The upper layer of Titan's hazes is still illuminated by sunlight."[90]





Blue halo stars[edit]

"The distribution of the high-latitude faint blue stars over Teff ... [shows] that the principal sequence [has] two gaps, at colors corresponding to log Teff ~ 4.11 (gap 1) and log Teff ~ 4.33 (gap 2). ... [T]he gaps [may be] a horizontal-branch phenomenon. ... [C]urrent theoretical concepts of the advanced evolution of Population II stars can explain the majority of blue halo stars.”[93]

Blue stragglers[edit]

This Hubble Space Telescope image of NGC 6397 shows a number of bright blue stragglers present.[94] Credit: NASA.

Blue stragglers (BSS) are main sequence stars in open or globular clusters that are more luminous and bluer than stars at the main sequence turn-off point for the cluster. Standard theories of stellar evolution hold that the position of a star on the Hertzsprung–Russell diagram should be determined almost entirely by the initial mass of the star and its age. In a cluster, stars all formed at approximately the same time, and thus in an H–R diagram for a cluster, all stars should lie along a clearly defined curve set by the age of the cluster, with the positions of individual stars on that curve determined solely by their initial mass. With masses two to three times that of the rest of the main sequence cluster stars, blue stragglers seem to be exceptions to this rule.[95] The resolution of this problem is likely related to interactions between two or more stars in the dense confines of the clusters in which blue stragglers are found.

Hypervelocity stars[edit]

When a star is born, a chaotic blue light show ensues. Credit: ESA/Hubble/NASA/K. Stapelfeldt.{{free media}}

"To date, all of the reported hypervelocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young.”[96]

"When a star is born, a chaotic [blue] light show ensues."[97] The image on the right shows five, chaotic, ghostly blue light shows which are "vivid bright clumps moving through the cosmos at some 1,000 light years from Earth."[97]

"Seen as the vivid blue, ephemeral clumps in the [image on the right], these are telltale signs of an energy-rich gas, or plasma, colliding with a huge collection of dust and gas in deep space."[97]

These "blue masses are transient creations in the cosmos, as they disappear into nothingness within a few tens of thousands of years."[98]

"These blue clumps are traveling at 150,000 mph toward the upper left direction (from our view, anyhow)."[97]

The "new star itself [is] called SVS 13, [...] it's obscured by thick clouds of cosmic matter."[97]

Luminous blue variables[edit]

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.[99]

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.

Blue outliers[edit]

There are faraway active galaxies that show a blueshift in their [O III] emission lines. One of the largest blueshifts is found in the narrow-line quasar, PG 1543+489, which has a relative velocity of -1150 km/s.[100] These types of galaxies are called "blue outliers".[100]

Blue dwarfs[edit]

"The Algol-type binaries are close, semi-detached, interacting binary star systems which contain a cool F–K giant or sub-giant secondary star that fills its Roche lobe and is losing mass to a hot B–A main sequence primary star."[101]

"The Algols contain a hot blue dwarf star with a magnetically-active late-type companion. In the close Algols, the gas stream flows directly into the photosphere of the blue mass-gaining star because it does not have enough room to avoid impact with that star."[101]

Blue giants[edit]

This is a schematic Hertzsprung-Russel diagram. Credit: Rursus.

A blue giant is a star with a spectral type of O or B (thus being noticeably blue in appearance) and a luminosity class of III (giant). In the standard Hertzsprung-Russell diagram, blue giants are found in the upper left corner, due to their high luminosity and early spectral type.

Def. a very hot and very luminous star that emits visible light in the blue portion of the spectrum is called a blue giant.

Blue-horizontal-branch stars[edit]

Notation: let the symbol BHB stand for Blue horizontal-branch.

"BHB stars are excellent tracers of Galactic halo dynamics because they are luminous and have a nearly constant absolute magnitude within a restricted color range"[102]

Blue subdwarfs[edit]

Blue “subdward B [stars] ... are difficult to fit into the evolutionary scheme.”[93]


Blue supergiants[edit]

Blue supergiants (BSGs) are supergiant stars (luminosity class I) of spectral type O or B. They are extremely hot and bright, with surface temperatures of 30,000-50,000 K. They can have radii up to about 25 solar radii. These rare and enigmatic stars are amongst the hottest and brightest in the known Universe.[104]

Def. a very large, hot and luminous star; a large blue giant is called a blue supergiant.


The NASA/ESA Hubble Space Telescope has captured a beautiful galaxy that, with its reddish and yellow central area, looks rather like an explosion from a Hollywood movie. Credit: ESA/Hubble & NASA.


"Schweizer [1978] defined five observational characteristics that unambiguously identified NGC 7252 as a late-stage merger ... One of these new characteristics is the blue portion of the optical spectrum of the main body."[105]

Blue shifts[edit]


Locations on Earth[edit]



The Collaboration between Australia and Nippon for a Gamma Ray Observatory in the Outback, (CANGAROO) is for very high energy cosmic gamma ray observation by telescope detecting Cherenkov light. It is located on the Woomera Prohibited Area in South Australia.[107]

Ancient history[edit]

The ancient history period dates from around 8,000 to 3,000 b2k.

"Beginning in about 2500 BC, the ancient Egyptians began to produce their own blue pigment known as Egyptian blue, made by grinding silica, lime, copper and alkali, and heating it to 800 or 900 degrees C. This is considered the first synthetic pigment.[108]



c2 = 1.438833 cm K may be used to approximate a pair such as (475 nm, 6300 K).

For a simple calculator, y=(1.48833/(0.0000475*6300))*exp(1.48833/(0.0000475*6300))/(exp(1.48833/(0.0000475*6300))-1)-5, followed by print y, yields a value close to zero (8.183732E-03). The closer to zero the more accurate the estimate.

Although Planck's equation is not an exact fit to a star's spectral radiance, it may be close enough to suggest if a star is an astronomical blue source using the above derivative.

From a Planckian spectrum peaked in the blue radiation band, the wavelength temperature pairs are approximately (450 nm, 6700 K) and (475 nm, 6300 K).


"Blue sensitive photodetectors have been fabricated from thallium bromide (TlBr) crystals for scintillation detection. Lu2SiO5 (LSO)/TlBr detectors consisting of 3 mm × 4 mm TlBr photodetectors coupled to 2 mm ×2 mm × 4 mm long LSO scintillators have demonstrated energy resolutions of 34.5% and 25.5% full width at half maximum for 511 keV and 662 keV γ rays, respectively."[110]

"ZnSe appears as an attractive material to blue and near UV optoelectronics."[111]


  1. All blue stars are not transparent.
  2. All blue stars occur at the center of the Galaxy.

See also[edit]


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Further reading[edit]


External links[edit]

{{Radiation astronomy resources}}