Radiation astronomy/Yellows

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Yellow astronomy is astronomy applied to the various extraterrestrial yellow sources of radiation, especially at night. It is also conducted above the Earth's atmosphere and at locations away from the Earth as a part of explorational (or exploratory) yellow astronomy.

This is a true-color image of Io taken by the Galileo probe. Credit: NASA.{{free media}}

Seeing the yellow Sun and feeling the warmth of its rays is probably a student's first encounter with an astronomical yellow radiation source.

There are yellow objects and emission lines in the yellow portion of the visible spectrum from 570 to 590 nm in wavelength.

Anasazi astronomyEdit

Diagram shows the location of the sun daggers on the petroglyph on various days. Credit: Nationalparks.{{free media}}

"When they [the Anasazi] built the kiva, they first put up beams of four different trees. These were the trees that were planted in the underworld for the people to climb up on. In the north, under the foundation they placed yellow turquoise; in the west, blue turquoise, in the south, red, and in the east, white turquoise."[1]

"The rising of the moon [on the morning of August 8, 1988. The moon's declination was 28.5°.] between the chimneys [of the kiva] is visible from the Chimney Rock Pueblo only at the times of major northern standstill occurring every 18.61 years."[1]


Color Frequency Wavelength
violet 668–789 THz 380–450 nm
blue 631–668 THz 450–475 nm
cyan 606–630 THz 476–495 nm
green 526–606 THz 495–570 nm
yellow 508–526 THz 570–590 nm
orange 484–508 THz 590–620 nm
red 400–484 THz 620–750 nm

"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."[2] 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."[3]

"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."[4]

"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."[5]

Planetary sciencesEdit

Fajada Butte is in Chaco Canyon, New Mexico. Credit: Rationalobserver.{{free media}}

"U-Pb ages of zircon from the Firehole and Analcite ash beds in the Eocene Green River Formation (Wyoming, United States) are indistinguishable from 40Ar/39Ar ages of sanidine after adjusting the latter to the astronomically calibrated age of 28.201 Ma for the Fish Canyon sanidine standard."[6]

"Calibrating Green River Formation 40Ar/39Ar ages to the 28.201 Ma age for Fish Canyon sanidine permits the first direct comparison of specific Green River Formation strata to the astronomical solution for Early Eocene insolation. This comparison supports the hypothesis that periods of fluvial deposition coincided with minima in long and short eccentricity, and that periods of lake expansion and evaporite deposition correspond to eccentricity maxima."[6]

"Euhedral, pale yellow zircons were isolated from the Analcite and Firehole ash beds by hand-crushing and heavy liquid concentration."[6]

Color astronomyEdit

These are examples of the various colors of yellow. Credit: Badseed.{{free media}}
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: Dicklyon.{{free media}}
The image is of a horse colored with yellow ochre. from Lascaux cave. Credit: Cro-Magnon peoples.{{free media}}
This shows a field of yellow rapeseed. Credit: Petr Kratochvil.{{free media}}

Def. "[t]he colour of gold or butter; the colour obtained by mixing green and red light, or by subtracting blue from white light"[7] is called yellow.


a bright yellow colour, resembling the metal gold

is called


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.


Citrine is a deep golden yellowish variety of quartz. Credit: Wela49.{{free media}}

Tarapacaite is a natural mineral pigment composed of potassium chromate which is a likely source of yellow.

Precious metal mineralsEdit

This is an image of a naturally occurring gold nugget. Credit: USGS.{{free media}}

At right is an image of a piece of native gold discovered as part of a placer deposit, a gold nugget.

Chalcogen mineralsEdit

The image shows native sulfur, yellow, and calcite crystals, clear or white. Credit: Didier Descouens.{{free media}}
This shows sulfur crystals from the Smithsonian Institution. Credit: Deglr6328.{{free media}}

Sulfur occurs naturally as the pure element (native sulfur) and as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses in ancient India, ancient Greece, China and Egypt. Octasulfur is a soft, bright-yellow solid with only a faint odor, similar to that of matches.


These are bronze to brass-yellow, striated, cyclically-twinned cubanite crystals from the Chibougamau mines of Quebec. Credit: Rob Lavinsky.{{free media}}

Cubanite is a yellow mineral of copper, iron, and sulfur, CuFe2S3.[8] Cubanite occurs in high temperature hydrothermal deposits with pyrrhotite and pentlandite as intergrowths with chalcopyrite. It results from exsolution from chalcopyrite at temperatures below 200 to 210 °C.[9] It has also been reported from carbonaceous chondrite meteorites.[9]


The image shows pale-yellow microlite on lepidolite. Credit: Rob Lavinsky.{{free media}}

Microlite is composed of sodium calcium tantalum oxide with a small amount of fluorine (Na,Ca)2Ta2O6(O,OH,F). Microlite is a mineral in the pyrochlore group that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a variable specific gravity of 4.2 to 6.4. It occurs as disseminated microscopic subtranslucent to opaque octahedral crystals with a refractive index of 2.0 to 2.2. Microlite is also called djalmaite. Microlite occurs as a primary mineral in lithium-bearing granite pegmatites, and in miarolitic cavities in granites.


Orpiment is a yellow to orange mineral on Earth. Credit: USGS.{{free media}}

Orpiment, [Arsenic trisulfide] As2S3, is a common monoclinic arsenic sulfide mineral. Orpiment is an orange to yellow mineral that is found worldwide [on Earth], and occurs as a sublimation product in volcanic fumaroles, low temperature hydrothermal veins, hot springs and as a byproduct of the decay of another arsenic mineral, realgar.


Pyrite cubic crystals are on marl from Navajún, Rioja, Spain. Credit: CarlesMillan.{{free media}}

The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale brass-yellow hue have earned it the nickname fool's gold because of its superficial resemblance to gold. Pyrite is the most common of the sulfide minerals [on Earth]. Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds, and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold.[10]


This Satterlyite sample is from the Rapid Creek area of northern Yukon, Canada. Credit: Chris857.{{free media}}

Satterlyite is a hydroxyl bearing iron phosphate mineral. The mineral can be found in phosphetic shales. Satterlyite is part of the phosphate mineral group. Satterlyite is a transparent, light brown to light yellow mineral. Satterlyite has a formula of (Fe2+,Mg,Fe3+)2(PO4)(OH). Satterlyite occurs in nodules in shale in the Big Fish River (Mandarino, 1978). These nodules were about 10 cm in diameter, some would consist of satterlyite only and others would show satterlyite with quartz, pyrite, wolfeite or maricite.

"Holtedahlite, a mineral that was found in Tingelstadtjern quarry in Norway, with the formula (Mg12PO4)5(PO3OH,CO3)(OH,O)6 is isostructural with satterlyite (Raade, 1979). Infrared absorption powder spectra show that satterlyite is different than natural haltedahlite in that there is no carbonate for phosphate substitution (Kolitsch, 2002). Satterlyite is also structurally related to phosphoellenbergerite, a mineral that was discovered in Modum, Norway; near San Giocomo Vallone Di Gilba, in Western Alps of Italy (Palache, 1951); the minerals formula is Mg14(PO4)5(PO3OH)2(OH)6 (Kolitsch, 2002).

Actinide mineralsEdit

The Carnotite is from the Happy Jack Mine, Utah. Credit: USGS.{{free media}}

Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K2(UO2)2(VO4)2·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present. ... Carnotite is a bright to greenish yellow mineral that occurs typically as crusts and flakes in sandstones. Amounts as low as one percent will color the sandstone a bright yellow. The high uranium content makes carnotite an important uranium ore and also radioactive. It is a secondary vanadium and uranium mineral usually found in sedimentary rocks in arid climates. It is an important ore of uranium in the Colorado Plateau region of the United States where it occurs as disseminations in sandstone and concentrations around petrified logs.

Silicate mineralsEdit

This image shows yellow-brown spurrite from New Mexico, USA. Credit: Dave Dyet.{{free media}}

Spurrite is a nesosilicate that can occur naturally as a yellow mineral. "Its chemical formula is Ca5(SiO4)2CO3.[11] Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks.[12]


Limonite is an amorphous mineraloid of a range of hydrated iron oxides. Credit: USGS.{{free media}}

Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two principle iron ores, the other being hematite, and has been mined for the production of iron since at least 2500 BCE.[13][14] Although originally defined as a single mineral, limonite is now recognized as a mixture of related hydrated iron oxide minerals, among them goethite, akaganeite, lepidocrocite, and jarosite. Individual minerals in limonite may form crystals, but limonite does not, although specimens may show a fibrous or microcrystalline structure,[15] and limonite often occurs in concretionary forms or in compact and earthy masses; sometimes mammillary, botryoidal, reniform or stalactitic. Because of its amorphous nature, and occurrence in hydrated areas limonite often presents as a clay or mudstone. However there are limonite pseudomorphs after other minerals such as pyrite.[16] This means that chemical weathering transforms the crystals of pyrite into limonite by hydrating the molecules, but the external shape of the pyrite crystal remains. Limonite pseudomorphs have also been formed from other iron oxides, hematite and magnetite; from the carbonate siderite and from iron rich silicates such as almandine garnets. Limonite usually forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron rich sulfide minerals, and chemical weathering of other iron rich minerals such as olivine, pyroxene, amphibole, and biotite. It is often the major iron component in lateritic soils. One of the first uses was as a pigment. The yellow form produced yellow ochre for which Cyprus was famous.[17]

Theoretical yellow astronomyEdit

Sprites are imaged above Kansas on 10 August 2000. Credit: Bob Jackson~commonswiki.{{free media}}

Here's a theoretical definition:

Def. astronomy applied to the various terrestrial or extraterrestrial yellow sources of radiation, especially at night is called yellow astronomy.

It is also conducted above the Earth's atmosphere and at locations away from the Earth as a part of explorational (or exploratory) yellow astronomy.

"The lack of long period Cepheids of Population I with P > 45 d in the Galaxy as opposed to the Magellanic Clouds, has fascinated observers and theoreticians for many years."[18]


A Statue of Krishna in the Sri Mariamman Temple, Singapore has Krishna shown with a flute. Credit: AngMoKio.{{free media}}
This image shows the blue skinned Krishna with yellow silk dhoti. Credit: Nasir khan Saikat.{{fairuse}}
The image shows the classical planet Krishna leaning against a white cow. Credit: Parvati and Ossopunk.{{fairuse}}

Krishna is the Daśāvatāra eighth avatar incarnation of Lord Vishnu in Hinduism. Worship of the deity Krishna, either in the form of Vasudeva, Bala Krishna or Gopala can be traced to as early as 4th century BC.[19][20] He is often shown wearing a yellow silk dhoti and a peacock feather crown. The Harivamsa describes intricate relationships between Krishna Vasudeva, Sankarsana, Pradyumna and Aniruddha that would later form a Vaishnava concept of primary quadrupled expansion, or avatar.[21]

"The Hindu Atharva Veda speaks of the "four heavenly directions, having the wind as lord, upon which the sun looks out."63 This, of course, can only be the central sun, who is Brahma, a god of four faces. The myths also attribute four faces to Shiva.64 The central sun Prajapati takes the form of the four-eyed, four-faced, and four-armed Vivvakarman, the "all maker".65 Agni, too, faces "in all directions,"66 as does Krishna.67 ... There can no longer be any doubt that the four-eyed or four-faced god is Saturn, for the sun-planet appears in Babylonian myth as Ea (Sumerian Enki)-a god of four eyes that "behold all things."73"[22]

"The bansuri is one of the most important instruments in Hindu mythology. It was the instrument played by Krishna, who Hindus believe is the eighth reincarnation of the god Vishnu, when he was in child form. Its use in Buddhist paintings can be identified as early as CE 100."[23]

Radiation astronomy sourcesEdit

Mount Redoubt in Alaska erupted on April 21, 1990. The mushroom-shaped plume rose from avalanches of hot debris that cascaded down the north flank. Credit: R. Clucas, USGS.{{free media}}

Notation: let the symbol EMSS represent the Einstein Medium Sensitivity Survey.

The "presence of an excess of X-ray luminous "yellow" stars, already found with the analysis of the stellar content of the Einstein Medium Sensitivity Survey (MSS), is confirmed by the EMSS, whose substantially larger size sample allows to draw conclusions with a higher statistical significance than the MSS"[24].

An "excess of X-ray luminous "yellow" stars in the X-ray selected samples, [have been] tentatively identified with a population of active RS CVn-like binaries, or a population of active young late-type stars."[24]

"The comparison between ... model predictions and the observed stellar source counts for yellow stars in the reference EMSS subsample shows a clear excess that peaks in the F-G spectral type range where the 70 observed sources have to be compared with the ~24 predicted ones. This excess is statistically significant at more than 99.8% level. ... this excess is concentrated for B - V ranging from 0.5 to 1.0 (corresponding to mv ranging from 8 to 12) which corresponds, in the EMSS, to normal main sequence stars with spectral type comprised between F and early K."[24]

This "excess is real, and most likely doe to some high X-ray luminosity population with optical characteristics similar to normal main sequence yellow stars."[24]

There is also "an excess for the A/F star groups mainly due to the occurrence of stars with fx/fv ratio higher than the mean values for each group and suggest that this could be explained by the occurrence of a large number of X-ray unresolved binary systems with an active M star companion than the predicted ones."[24]

"For yellow stars, the current state-of-art knowledge in terms of X-ray luminosity functions is not able to account for all of the observed yellow stellar sources in the EMSS, so that, to explain the observed source counts, a new population of stellar-like X-ray emitting sources with optical characteristics similar to normal main sequence yellow stars must be hypothesized. ... based on current knowledge, this population is likely to be (at least partly) composed of very young (and therefore highly X-ray luminous) yellow stars, perhaps of the kind variously indicated by previous authors as WTTS or NTTS, or simply by near ZAMS objects."[24]


The NASA/ESA Hubble Space Telescope has snapped a striking view of a multiple star system called XZ Tauri, its neighbour HL Tauri and several nearby young stellar objects. Credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt.{{free media}}

XZ Tauri is blowing a hot bubble of gas into the surrounding space, which is filled with bright and beautiful clumps that are emitting strong winds and jets. These objects illuminate the region.

"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."[25]


Yellow continua is exhibited during a sunset in Rio de Janeiro. Credit: Rosimeria.{{free media}}

In Fig. 4, "A density tracing of the spectrum of θ Lyr, K0 II. Straight chords through the yellow continuum toward the blue and from λ 4750 along the green depression to the Mg I "b" triplet lines define the break-angle α (α here is about 12°)."[26]


Observations reveal [Fe II] emission, shown here in pink, along the edges of the biopolar outflows of this young planetary nebula. Credit: Judy Schmidt from USA.{{free media}}

Red screen: F164N ([Fe II]) Red: F673N Yellow-Green: F658N Blue: F373N. North is 35.20° clockwise from up.

Emission lines are usually unique to the chemical elements. As the emissions are produced by the release of specific wavelength photons when electrons drop to a lower energy level, absorption lines may be produced as electrons rise to this higher energy level.


Sunset is in Wiltshire. Credit: Stewart Black.{{free media}}

"Data in two spectral bands (green: λ 5253-5353, and yellow: λ 5824-5844) were taken on several sunspot groups during February 1974. ... the general level of circular polarization is weaker [in the yellow band]. The peak magnitudes of the linear polarization [PL ≡ (Q2 + U2)½/I] (Figs. 1C and 2C) are comparable in both colors; the spatial distribution is, however, markedly different. Whereas in the green PL is fairly uniform over both type 1 [penumbra] and 2 ["speckled" possibly umbra] regions, in the yellow PL appears strong only in region 2; the linear polarization associated with region 1 has nearly vanished."[27]

"The behavior of the azimuth of the linear polarization at various points in the sunspot is markedly different in the two colors. In the green, one can clearly see a generally radial pattern over the entire spot; no such general pattern is apparent in the yellow, but a less pronounced radial pattern in the core of the spot does remain. It should be noted that the more complex area in the green corresponds to the "speckled" type 2 region."[27] {[clear}}


It was a beautiful view from Narendra nagar on the way from Tehri garhwal about 5:00 pm. Credit: Naresh Sirola.{{free media}}

"To greet the eyes of visitors as they first enter the Planetarium Building, there is planned a large decorative painting in oil, in three panels, illustrating American Indian astronomical mythology. Although primarily from the Blackfeet, the myths selected are those of rather wide distribution with little variation among the various tribes of North America. The left panel shows the Northern Lights or Aurora Borealis in the form of an arch in all the delicate colors, in which may be dimly seen the figures of the White Men of the North dancing around their camp-fires. The central panel shows the sun-god on a brilliant yellow background, the moon-goddess on a paler background, while in the upper right may be seen the Pleiades as conceived by the Indians, and in the upper left the Big Dipper and the North Star, these corner representations with the Milky Way or sky-trail between them are shown in silver on a background of deep blue."[28]

"Placed between two Nicols, the [quartz] plate has the appearance [:] When the corresponding diagonals of the Nicols are parallel, or nearly so, the bands arc white upon a deep reddish-purple ground, [...]; with the Nicols crossed, the bands are dark upon a light greenish-yellow background, [...]."[29]

"The quartz plate was placed in one end of a tube, large enough to admit its full size very nearly, and 11 inches in length. [...] In the other end was placed a good-sized Nicol; [...] Thus mounted the plate and Nicol form a polariscope of extraordinary sensibility, with faint light far excelling the best Savart, and even with strong light somewhat superior to it."[29]

"The instrument is especially suited for the determination of small degrees of polarization, and the examination of very faint lights."[29]

Observations "upon the zodiacal light [...] made to determine whether or not any portion of the light is polarized, [...] the amount of polarization necessary increases very greatly as the light becomes fainter, and especially so as it approaches the limit of visibility."[29]

"On the completion of the instrument the first favourable opportunity was improved to test its efficiency upon the zodiacal light. It was almost immediately found to indicate the existence of light polarized in a plane passing through the sun. The bands were fainter than had been expected, and at first were overlooked. [...] On looking through the tube at the zodiacal, and turning the whole instrument slowly round, it was possible to find a position where the bands could be seen, and their nature and direction determined."[29]

"The results of the numerous observations of different evenings were entirely concordant, and showed that the plane of polarization passes through the sun, as nearly as it was possible to fix its direction."[29]

"The fact of polarization implies that the light is reflected, either wholly or in part, and is thus derived originally from the sun."[29]

"The results of the investigation may be summarized as follows:"[29]

  1. The zodiacal light is polarized in a plane passing through the sun.
  2. The amount of polarization is, with a high degree of probability, as much as 15 per cent., but can hardly be as much as 20 per cent.
  3. The spectrum of the light is not perceptibly different from that of sunlight, except in intensity.
  4. The light is derived from the sun, and is reflected from solid matter.
  5. This solid matter consists of small bodies (meteoroids) revolving about the sun in orbits crowded together toward the ecliptic.


This astronaut photograph was taken from the International Space Station while over China (approximately 400 kilometres to the north-west of Beijing), provides the unusual perspective of looking down on a meteor as it passes through the atmosphere. Credit: ISS Expedition 28 crew.{{free media}}

"The train spectrum consisted of a red continuum, yellow continuum, and about 50 atomic lines between 3700–9000 Å. The yellow continuum, possibly due to NO2, was also detected in the persistent train."[30]

"On November 18, 1999 at 04h00m29s UT, about two hours after the maximum of the 1999 Leonid meteor storm, a very bright Leonid meteor appeared over the island of Corse, France, and produced an afterglow evolving into a persistent train that was visible to the naked eye for several minutes."[30]

Cosmic raysEdit

The W44 supernova remnant is nestled within and interacting with the molecular cloud that formed its parent star. Credit: NASA/DOE/Fermi LAT Collaboration, NRAO/AUI, JPL-Caltech, ROSAT.{{free media}}

Fermi's LAT detects GeV gamma rays (magenta) produced when the gas is bombarded by cosmic rays, primarily protons. Radio observations (yellow) from the Karl G. Jansky Very Large Array near Socorro, N.M., and infrared (red) data from NASA's Spitzer Space Telescope reveal filamentary structures in the remnant's shell. Blue shows X-ray emission mapped by the Germany-led ROSAT mission.

"The yellow supergiant content of nearby galaxies can provide a critical test of stellar evolution theory, bridging the gap between the hot, massive stars and the cool red supergiants. But, this region of the color-magnitude diagram is dominated by foreground contamination, requiring membership to somehow be determined."[31]

"The program exposures were extracted, using the dome flat field exposures as reference, and wavelength corrected. As the He-Ne-Ar exposures were obtained in the afternoon, and the grating might even be removed and reinserted before the program exposures, a zero-point shift in wavelength was determined for each of the M31 spectra using the O I λ5577 night sky line. ... Consecutive exposures of each M31 configuration were then summed, after cosmic rays were first identified and removed by comparing a median of the exposures to the individual exposures."[31] Bold added.


Observations by NASA's 2001 Mars Odyssey spacecraft show a global view of Mars in intermediate-energy, or epithermal, neutrons. Credit: NASA/JPL/University of Arizona/Los Alamos National Laboratories.{{free media}}

Soil enriched by hydrogen is indicated by the deep blue colors on the map, which show a low intensity of epithermal neutrons. Progressively smaller amounts of hydrogen are shown in the colors light blue, green, yellow and red. The deep blue areas in the polar regions are believed to contain up to 50 percent water ice in the upper one meter (three feet) of the soil. Hydrogen in the far north is hidden at this time beneath a layer of carbon dioxide frost (dry ice). Light blue regions near the equator contain slightly enhanced near-surface hydrogen, which is most likely chemically or physically bound because water ice is not stable near the equator. The view shown here is a map of measurements made during the first three months of mapping using the neutron spectrometer instrument, part of the gamma ray spectrometer instrument suite. The central meridian in this projection is zero degrees longitude. Topographic features are superimposed on the map for geographic reference.

"A comparison of the heavy-element abundance distribution in [AG Draconis] with theoretical nucleosynthesis calculations shows that the s-process is defined by a relatively large neutron exposure (τ=1.3 mb-1), while an analysis of the rubidium abundance suggests that the s-process occurred at a neutron density of about 2 [x] 108 cm-3."[25]

The "K giant in AG Dra [has a] Teff ~ 4100 - 4400 K. ... [With a best fit to spectroscopic data of Teff = 4300 K.]"[25]

Observed heavy-element abundances may be used "to probe two aspects of the s-process:

  1. ... the relative abundance distribution of elements analysed ... [determines] the neutron exposure τ characterizing the s-process efficiency, and
  2. ... the abundance of Rb ... is sensitive to neutron density [providing] constraints on the s-process neutron density Nn."[25]

The "s-process branch point [is] at the β-unstable nucleus 85Kr ...

  1. dominated by 85Rb (at 'low' neutron densities) or
  2. 87Rb (at 'high' neutron densities)."[25]

Due to the difference "in neutron-capture cross sections" (σ), σ(85Rb)/σ(87Rb) ~ 25, "the s-process abundance of Rb increases dramatically with increasing neutron density. The Rb abundances have been used to infer neutron densities in both

  1. a small number of barium stars ... and in
  2. three metal-poor giants of the globular cluster ω Cen."[25]

Comparison shows "a clear and striking increase in the [Rb/Zr] ratio with decreasing [Fe/H] ratio ... is evidence of an increasing s-process neutron density with decreasing metallicity."[25]

Numbers "from Malaney & Lambert (1988) and Malaney (1987a) [can be used] to determine the s-process abundance ratio Rb/Zr as a function of the neutron density Nn. ... [First the observed abundances are corrected for previous in flow.] ... ignoring the one extremely Rb-rich ω Cen giant ... The other 8 stars are characterized extremely well by a linear increase of log Nn with decreasing [Fe/H]".[25]


3D view of an event recorded with the CMS detector in 2012 at a proton-proton centre of mass energy of 8 TeV. Credit: McCauley, Thomas; Taylor, Lucas; for the CMS Collaboration.{{free media}}

The event shows characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers). The event could also be due to known standard model background processes.

"As a result of ion irradiation a modification (evolution) of the original target can be generated and new materials can be produced. Bonds in the target material may in fact be broken by energy deposition around the "hot" track of incoming ions. The recombination of fragments produces new and also complex molecules. If carbon is present in the target, even long chain polymer-like substances that are stable above room temperature can be produced ... The presence of organic material in the [solar system], possibly produced by bombarding ions ... seems now well supported by recent findings from space missions as from Voyager at the Uranian system".[32]

The "colour of the organic layers [synthesized organic samples of frozen CH4 (T ~ 10 K) ice] depends on the amount of energy deposited by the bombarding beam [~ 1016 protons (1.5 MeV) cm-2 and ~ 1017 protons cm-2]. When first extracted after a (relatively) low ion fluence the materials appear yellow, becoming darker and darker if again bombarded at higher doses."[32]

"The evolution of organics to carbonaceous material induced by ion irradiation is ... a well established phenomenon independent of the type of original carbon containing material."[32]


Colorized SEM-image shows pyrite nanocrystals (yellow octahedra) in an ore matrix. Credit: TiberiusRufus.{{free media}}

"The temperature of yellow coronal regions is ... about 2.5 [x] 106 [K]. ... although some ions Ca XV will exist at lower, as well as higher temperatures."[33]

"The AS prominences [AS in Menzel-Evans' classification [4];] move with velocities exceeding by far the velocities of other types of prominences [7], [8]. As short-living phenomena, they are condensed quickly and the temperature of the coronal gases should rise in the early stages of their condensation. Indeed, the AS prominences use to be allied with yello line emission (λ 5694)."[33]

"The yellow line is namely due to the ion Ca XV, according to Edlen's and Waldmeier's identification. ... the line λ 5694 is emitted by 3P1 - 3P0 transition of Ca XV."[33]

"The solar corona is not in thermodynamical equilibrium. In particular, the photo-recombination is compensated with electron impact ionization, while the reverse processes viz. the photoionization and recombination by impact with two electrons are there negligible."[33]


Simulation of a terrestrial gamma-ray flash (magenta) shows associated electron/positron beams (yellow/green) along a magnetic field line. Credit: NASA's Goddard Space Flight Center.{{free media}}

Calculations of "the changes in the surface chemical composition of intermediate-mass stars in the first phase of convection dredge-up ... has been used to determine the changes in the surface chemical composition of stars with masses 2.5, 5, 10, 20 Mʘ due to nuclear reactions of the pp chains, the triple CNO cycle, and the NeNa and MgAl cycles."[34]

"We followed the changes that take place in 30 reactions in the abundances of the electrons, positrons, and 24 nuclides, a complete list of which, together with their initial abundances (in the proportions of Cameron [i0]), is given in [17]."[34]

Plasma objectsEdit

This photo of yellow and green auroras shows convincingly that yellow is a distinctive result of the auroral process. Credit: Belinda Witzenhausen.{{fairuse}}
This image captures an unusual aurora from Urengoi, Russia. Credit: Unknown.{{fairuse}}
This aurora image from Alaska shows distinctive yellow associated with the horizon. Credit: Unknown.{{fairuse}}
This is another aurora from Alaska containing yellow. Credit: Unknown.{{fairuse}}
This orange and yellow aurora occurred above Beaghmore Stone Circles. Credit: Martin McKenna.{{fairuse}}

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."[35]

"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."[35]

Gaseous objectsEdit

Close to a bright, nearby star in this image, the bizarre, whorl-shaped object known as IRAS 22036+5306 has been captured during a brief tumultuous period late in a star's life. Credit: NASA/ESA Hubble Space Telescope.{{free media}}

Inside IRAS 22036+5306 lies an aged star that has coughed off almost all of its outer material, forming a cloud in space. Hidden under this veil, the dense, still-burning, exposed core of the star grows hotter. Encircling the star is a torus consisting partly of castoff material, as well as possibly the grainy remnants of comets and other small, rocky bodies. Twin jets spout from the star’s poles and pierce this dusty waist. The jets contain gobbets of material — typically about ten thousand times the mass of the Earth — hurling outwards at a speed of nearly 800 000 kilometres per hour.

IRAS 22036+5306 is making the transition through the protoplanetary, or preplanetary, nebula phase. Only a few hundred such nebulae have been spotted in our galaxy. For now, light from the central star is merely being reflected off its expelled gaseous shell. Soon, however, the star will become a very hot, white dwarf, and its intense ultraviolet radiation will ionise the blown-off gas, making it glow in rich colours. IRAS 22036+5306 will have then blossomed into a fully-fledged planetary nebula, and this event will serve as a last hurrah before the star starts its very slow final cool-down.

Planetary nebulae are much longer-lived than their precursors, protoplanetary nebulae, and are therefore more commonly spotted. The term planetary nebula is a leftover from observations through small telescopes made by early astronomers to whom some of these objects looked circular and similar in appearance to the outer planets Uranus and Neptune.

IRAS 22036+5306 is found about 6500 light-years away in the constellation of Cepheus (The King).

Liquid objectsEdit

This picture of the sun is like a golden liquid during sunset. Credit: Madheswaran.{{free media}}

A sunset here appears like a golden liquid.

Rocky objectsEdit

Sulfur deposits are shown from the Yellowstone Caldera. Credit: Daniel Mayer.{{free media}}

"Euhedral crystals [from the Lodran meteorite AMNH 314] of olivine and clear pale yellow fragments of orthopyroxene (Opx) and two green grains were examined by precession camera."[36]


The spectrum shows the lines in the visible due to emission from elemental helium. Credit:Teravolt.{{free media}}
This is a spectrum of Ring Nebula (M57) in range 450.0 — 672.0 nm. Credit: Minami Himemiya.{{free media}}

"The helium emission lines behave in a qualitatively similar way to the calcium triplet. The 5876 Å line (Fig. 1e) is the dominant line in all the spectra, although two other transitions (6678 and 7065) are also in emission in most of the stars and have nearly identical profiles."[37] He I is 587.6 nm, a yellow emission line. The He I photospheric emission line "narrow component is present in emission ... with [chromospheric] veilings larger than 0.4, being conspicuous even in those heavily veiled stars".[38] The chromospheric veiling apparently results in the emission broadening of the He I emission from the chromosphere which is partially added to the He I narrow emission from the photosphere.[38]

"The radiative loss for both broad and narrow emission--i.e., the excess of emission over the external continuum expressed in percentages of the photospheric fluxes--is Fph(1 + ν)EWobs, where Fph is the nearby photospheric flux and EWobs is the equivalent width of the observed emission component."[38] "[B]y assumption, [the dynamo] controls the narrow component fluxes."[38]

In the spectrum at right the yellow He I emission line is detected and recorded at normalized intensities (to the oxygen III line) from the Ring Nebula.


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

Carbon has one line in the yellow.


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

Nitrogen has a yellow forbidden line, specifically N II at 575.5 nm, that may be used to indicate nitrogen abundances and contribute to nitrogen/oxygen (N/O) abundance gradients. Surveys of H II regions in spiral galaxies have suggested that N/O abundance ratios increase from outer-arm nebulae to inner-arm nebulae.[39] "Electron temperatures are generally derived from the ratio of auroral to nebular lines in [O III] or [N II]."[40] "[B]ecause of the proximity of strong night-sky lines at λ4358 and λλ5770, 5791, the auroral lines of [O III] λ4363 and [N II] λ5755 are often contaminated."[40]

"The nitrogen abundance appears to increase with decreasing galactocentric distance. ... A least-squares solution weighting the points equally gives a magnitude for the gradient d(log N/H)/dr = -0.10 ± 0.03 kpc-1."[40] "The ratio N/O clearly increases with decreasing R. A least-squares fit to the data ... gives d(log N/O)/dr = -0.06 ± 0.02 kpc-1."[40]


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

Oxygen has two yellow lines.


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

Fluorine has several lines in the yellow as shown in the above spectrum.


This is a visual spectrum of neon showing its many emission lines. Credit: McZusatz.{{free media}}

There is a "bright yellow line of neon X [at] 5852.488 [Å, 585.2488 nm.]"[41]


Sodium spectrum is ringrising 400 nm - 700 nm Credit: McZusatz.{{free media}}

Fraunhofer's original (1817) designations of absorption lines in the solar spectrum

Letter Wavelength (nm) Chemical origin Colour range
atmospheric O2
dark red
atmospheric O2
hydrogen alpha
neutral sodium
red orange
neutral sodium
neutral iron
hydrogen beta
ionised calcium
dark violet
ionised calcium
dark violet"

Sodium produces two spectral lines known as D1 and D2, or the "sodium doublet". Their average wavelength, 589.3 nm, is often just called "D".

Def. "[a] street lamp in which electricity is passed through sodium vapour to emit a yellow light", from Wiktionary sodium vapor lamp, is called a sodium vapor lamp.


Calcium spectrum is 400 nm - 700 nm. Credit: McZusatz.{{free media}}

During the limb flares of December 18, 1956, a coronal line at 569.4 nm, a yellow line, occurred at 1822 UTC, 1900 UTC, undiminished up to 20,000 km above the solar limb, and at 2226 UTC, is identified as Ca XV.[42] "The coronal temperature was 4000000°."[42] "The December 18, 1956, flare appears to have been a violent condensation of material from a dense coronal cloud above an active region."[42]


Microstructure of rolled and annealed brass is shown at magnification 400X. Credit: Strangerhahaha.{{free media}}

The earliest brasses may have been natural alloys made by smelting zinc-rich copper ores.[43]


This is a visual image of the Sun with some sunspots visible. The two small spots in the middle have about the same diameter as our planet Earth. Credit: NASA.{{free media}}
This graph shows the temperature and density of the Sun's atmosphere from Skylab observations. Credit: John A. Eddy, NASA.{{free media}}

A natural division of astronomical bodies, or objects, between rocky bodies, astronomical objects with solid surfaces, or solids and liquids predominately on the surface, and gas bodies, astronomical objects with gases predominately detected and apparently constituting a surface, may be an informative approach toward stellar science.

Depending primarily upon gas temperature, the presence of gas may be used to determine the composition of the gas body observed, at least the outer layer. Early spectroscopy[44] of the Sun using estimates of "the line intensities of several lines by eye [to derive] the abundances of ... elements ... [concluded] that the Sun [is] largely made of hydrogen."[45]

The second image at right describes graphically the temperature and density of the Sun's atmosphere from the photosphere upwards. "The Sun's photosphere has a temperature between 4500 and 6000 K[46] (with an effective temperature of 5777 K) and a density of about [2 x 10-4kg/m3;[47] other stars may have hotter or cooler photospheres. The Sun's photosphere is composed of convection cells called granules—cells of gas each approximately 1000 km in diameter[48] with hot rising gas in the center and cooler gas falling in the narrow spaces between them. Each granule has a lifespan of only about eight minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are super granules up to 30,000 kilometers in diameter with lifespans of up to 24 hours. These details are too fine to see on other stars.


This orthographic projection view provides a look at Mercury's north polar region. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.{{free media}}

This orthographic projection view provides a look at Mercury's north polar region. The yellow regions in many of the craters mark locations that show evidence for water ice, as detected by Earth-based radar observations from Arecibo Observatory in Puerto Rico. MESSENGER has collected compelling new evidence that the deposits are indeed water ice, including imaging within the permanently shaded interiors of some of the craters, such as Prokofiev and Fuller.

Instrument: Mercury Dual Imaging System (MDIS) Arecibo Radar Image: In yellow (Harmon et al., 2011, Icarus 211, 37-50).

"[H]igh-resolution spectral measurements of Mercury show emission in sodium D lines (Potter and Morgan 1985a). This suggests a substantial sodium population in Mercury's atmosphere ... possibly due to photo-sputtering of the planetary surface".[49]


Using an imaging radar technique, the Magellan spacecraft was able to lift the veil from the face of Venus and produce this spectacular high resolution image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. Credit: Magellan Team, JPL, NASA.{{free media}}

Using an imaging radar technique, the Magellan spacecraft was able to lift the veil from the Face of Venus and produce this spectacular high resolution image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. This 3-kilometer resolution map is a composite of Magellan images compiled between 1990 and 1994. Gaps were filled in by the Earth-based Arecibo Radio Telescope. The large yellow/red area in the north is Ishtar Terra featuring Maxwell Montes, the largest mountain on Venus. The large highland regions are analogous to continents on Earth.

"Selected images of Venus [show] cloud configurations in yellow light".[50] These images are photographs taken between October 3, 1943, and March 14, 1945.[50]


The image shows the Sahara desert from space. Credit: NASA.{{free media}}

"Spectral properties of certain palagonitic soils found on Mauna Kea, Hawaii are similar to the spectral properties measured by earth-based telescopes for Martian soils [1,2,3]. ... Three layers with distinctly different colors (upper red, middle black, lower yellow) were sampled from hydrothermally altered basaltic tephra just below the summit of Mauna Kea."[51]

"The clay fractions (< 2 µm) of three palagonite samples-MK11 (red), MK12 (black), and MK13 (yellow) collected at an elevation of 4145 meters near the summit of Mauna Kea volcano in Hawaii ... The fine fractions of the black (MK12) and yellow (MK13) samples were similar to those of martian bright regions in terms of their overall shape."[52]

At right is a composite image of the Sahara. Most of the images are from the MODIS imager onboard the Terra satellite.


Big orange-yellowish moon is always observed on the 15th of each lunar month. Credit: GeorgeTan # 2...thanks for millionth support from Singapore.{{free media}}

"There is ... a dearth of basalt compositions corresponding to differentiates of the yellow glasses. ... After olivine and chromite, differentiates of the Apollo 14 and 17 yellow glass magmas should differ only slightly in crystallization sequence. ... For green and yellow glasses, liquids are saturated only with olivine and chromite; for red and black glasses, negative slope represents liquids saturated with olivine and chromite, positive slope indicates olivine, chromite, and armalcolite."[53]

"An unusual yellowish glass is found in the interstices, in fracture fillings, and as encrustations of a few uncommon, mildly fragmented KREEP basalt particles in Apollo 15 soils."[54]

Ferrobasalts in the Apollo 11 specimens have yellow materials present. "Irregular fragments of vesicular glass, pale yellow to golden brown are abundant. Some are up to half a millimeter across."[55]


The Martian sky at noon is yellow-brown, which contrasts with its pinkish-red color at sunset. Credit: NASA/JPL-Caltech.{{free media}}

The true color of Mars based upon three filters with the sky set to a luminance of 60. The color of the Pathfinder landing site is yellowish brown with only subtle variations. These colors are identical to the measured colors of the Viking landing sites reported by Huck et al. [1977]. This image was taken near local noon on Sol 10.

"The most striking change in the nontronite was color. The original nontronite was olive-yellow, corresponding to 25.Y 6/6 in the Munsell color chart (3). The material shocked to 180 kbar turned yellow-brown, 1.0Y 5/6, and the nontronite brought to 300 kbar was strong brown, 7.5Y 4/6."[56]

"[L]ittle Fe+2 (... is the case for most yellow nontronites)."[56]


Io, the most volcanic body in the solar system, is seen in the highest resolution obtained to date by NASA's Galileo spacecraft. Credit: NASA.{{free media}}
This global view of Io, is obtained from the tenth orbit of Jupiter by NASA's Galileo spacecraft. Credit: NASA.{{free media}}
This image of Io continues to the left around the rocky object. Credit: NASA.{{free media}}
This composite of images from Galileo and Voyager 1 shows Io's north pole. Credit: U.S. Geological Survey and NASA.{{free media}}
This composite is of Io's south pole. Credit: U.S. Geological Survey and NASA.{{free media}}
In the same way that the Moon always has the same side facing Earth, Io always has the same side facing Jupiter. Credit: U.S. Geological Survey and NASA.{{free media}}

Io is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. With over 400 active volcanoes, Io is the most geologically active object in the Solar System.[57][58] Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur.

In the image at right, the smallest features that can be discerned are 2.5 kilometers in size. There are rugged mountains several kilometers high, layered materials forming plateaus, and many irregular depressions called volcanic calderas. Several of the dark, flow-like features correspond to hot spots, and may be active lava flows. There are no landforms resembling impact craters, as the volcanism covers the surface with new deposits much more rapidly than the flux of comets and asteroids can create large impact craters. The picture is centered on the side of Io that always faces away from Jupiter; north is to the top.

Color images acquired on September 7, 1996 have been merged with higher resolution images acquired on November 6, 1996 by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. The color is composed of data taken, at a range of 487,000 kilometers, in the near-infrared, green, and violet filters and has been enhanced to emphasize the extraordinary variations in color and brightness that characterize Io's face. The high resolution images were obtained at ranges which varied from 245,719 kilometers to 403,100 kilometers.

The second image at right is a global view of Jupiter's moon, Io, obtained during the tenth orbit of Jupiter by NASA's Galileo spacecraft. Io, which is slightly larger than Earth's moon, is the most volcanically active body in the solar system. In this enhanced color composite, deposits of sulfur dioxide frost appear in white and grey hues while yellowish and brownish hues are probably due to other sulfurous materials. Bright red materials, such as the prominent ring surrounding Pele, and "black" spots with low brightness mark areas of recent volcanic activity and are usually associated with high temperatures and surface changes. One of the most dramatic changes is the appearance of a new dark spot (upper right edge of Pele), 400 kilometers (250 miles)in diameter which surrounds a volcanic center named Pillan Patera. The dark spot did not exist in images obtained 5 months earlier, but Galileo imaged a 120 kilometer (75 mile) high plume erupting from this location during its ninth orbit. North is to the top of the picture which was taken on September 19, 1997 at a range of more than 500,000 kilometers (310,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.

The third image at right continues around Io to the left.

The fourth image is of Io's north pole. The new basemap and the polar images of Jupiter's moon Io was produced by combining the best images from both the Voyager 1 and Galileo Missions. Although the subjovian hemisphere of Io was poorly seen by Galileo, superbly detailed Voyager 1 images cover longitudes from 240 W to 40 W and the nearby southern latitudes. A monochrome mosaic of the highest resolution images from both Galileo and Voyager 1 was assembled that includes 51 Voyager 1 images with spatial resolutions sometimes exceeding the 1 km/pixel scale of the final mosaic. Because this mosaic is made up of images taken at various local times of day, care must be taken to note the solar illumination direction when deciding whether topographic features display positive or negative relief. In general, the illumination is from the west over longitudes 40 to 270 W, and from the east over longitudes 270 W to 40 W. Color information was later superimposed from Galileo low phase angle violet, green, and near-infrared (756 nanometer wavelength) images. The Galileo SSI camera's silicon CCD was sensitive to longer wavelengths than the vidicon cameras of Voyager, so that distinctions between red and yellow hues can be more easily discerned. The "true" colors that would be visible to the eye are similar but much more muted than shown here. Image resolutions range from 1 to 10 km/pixel along the equator, with the poorest coverage centered on longitude 50 W.

The fifth image is of Io's south pole.

The last image is an animated image showing a 1 Io day of rotation. "In the same way that the Moon always has the same side facing Earth, Io always has the same side facing Jupiter. The movie shows two speeded-up rotations of Io (a single rotation really takes 1.77 days), and begins with a view of the Jupiter-facing hemisphere. With rotation in an easterly direction, after two seconds the volcano Prometheus (on the equator) comes into view. The massive red deposit around Pele (seconds 5-10) is the most distinctive expression of volcanic activity on Io, and just to the north-west is the horse shoe-shaped Loki Patera, the most powerful volcano on Io. The animation was made using a computer program that wrapped the Io mosaic around a sphere to produce a globe. In all, 360 images were used, each differing by one degree in longitude from the previous image.


It may not look like much, but this blob shows a remarkable star named V766 Centauri (V766 Cen for short) and its close companion. Credit: European Southern Observatory.{{free media}}

A few years ago using ESO's Very Large Telescope Interferometer (VLTI) V766 Centauri was found to be something known as a yellow hypergiant, a massive and luminous type of star that is extremely rare — and extremely big! Measuring over 1400 times the diameter of the Sun, V766 Cen was not only the largest star of its type ever discovered, but also one of the ten largest stars ever found.

The Secchi Class II consists of yellow stars with evident metallic lines.

"The Harvard classification system is a one-dimensional classification scheme. Stars vary in surface temperature from about 2,000 to 40,000 kelvins. Physically, the classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest, as is done in the following table:

Class Temperature[59]
Conventional color Apparent color[60][61][62] Mass[59]
(solar masses, Mʘ)
(solar radii, Rʘ)
(bolometric, Lʘ)
Fraction of all
main sequence stars[63]
O ≥ 33,000 K blue blue ≥ 16 ≥ 6.6 ≥ 30,000 Weak ~0.00003%
B 10,000–33,000 K blue to blue white blue white 2.1–16 1.8–6.6 25–30,000 Medium 0.13%
A 7,500–10,000 K white white to blue white 1.4–2.1 1.4–1.8 5–25 Strong 0.6%
F 6,000–7,500 K yellowish white white 1.04–1.4 1.15–1.4 1.5–5 Medium 3%
G 5,200–6,000 K yellow yellowish white 0.8–1.04 0.96–1.15 0.6–1.5 Weak 7.6%
K 3,700–5,200 K orange yellow orange 0.45–0.8 0.7–0.96 0.08–0.6 Very weak 12.1%
M ≤ 3,700 K red orange red ≤ 0.45 ≤ 0.7 ≤ 0.08 Very weak 76.45%

Stars of spectral classes F and G, such as our sun Sol, have color temperatures that make them look "yellowish".[64] The first astronomer to classify stars according to their color was F. G. W. Struve in 1827. One of his classifications was flavae, or yellow, and this roughly corresponded to stars in the modern spectral range F5 to K0.[65] The Strömgren photometric system for stellar classification includes a 'y' or yellow filter that is centered at a wavelength of 550 nm and has a bandwidth of 20–30 nm.[66][67]

Yellow degeneratesEdit

The image is an optical negative centered on the SIMBAD coordinates J2000.0 for Van Maanen's star. Image is from the Palomar 48-inch Schmidt reflecting telescope. Van Maanen's star is the largest black dot center top right. Credit: NASA/IPAC Extragalactic Database.{{free media}}
This is an Hertzsprung-Russell diagram. Note that luminosity class VII has color class G stars within. Credit: Spacepotato.{{free media}}
GJ 3223 is also designated LHS 1547. It is a white dwarf that is also color class G, a yellow degenerate. Credit: Aladin at SIMBAD.{{free media}}

EG 5 is a yellow degenerate.[68] EG 5 is another designation for Van Maanen's star.[69]

Van Maanen's star (van Maanen 2) is a white dwarf star. Out of the white dwarfs known, it is the third closest to the Sun, after Sirius B and Procyon B, in that order, and the closest known solitary white dwarf.[70][71]

The optical negative at right was taken earlier than the current coordinates for Van Maanen's star, which are at the center of the negative.

Van Maanen's star has a radius of 9,000 ± 1,400 km.[72] It's effective surface temperature is 6,220 ± 240 K.[73]

Degenerate stars are white dwarfs of spectral luminosity class VII.

Some yellow degenerate stars are of white dwarf spectral type DC (which show no detectable lines) mostly below Teff < 10,000 K.[68]

At left is an Hertzsprung-Russell diagram which shows that luminosity class VII has color class G stars within.

At lower right is a close to true color visual image of GJ 3223, a yellow degenerate white dwarf.[68] It is similar to other luminosity class VII yellow degenerates LHS 3369 and LHS 3399. Each is color class G, often written "g"[68] when referring to white dwarfs.

Yellow subdwarfsEdit

Yellow subdwarfs are in luminosity class VI. "[Y]ellow high-velocity subdwarfs are easily confused with white dwarfs in a proper-motion selection."[68]

HD 64090 is a color class G0 subdwarf.

Yellow main sequence starsEdit

HD 86226 is a spectral type G2V yellow main sequence star. Credit: Aladin at SIMBAD.{{free media}}

The closest G2V yellow main sequence star is the Sun described above.

At right is a visual image in close to true color of the main sequence single star HD 86226. It has a parallax of 22.20 mas, but is not an X-ray source. A substellar companion HD 86226b has been detected.

Yellow subgiantsEdit

V972 Scorpii is a variable star of the delta Scuti type. Spectral type is G2IV. Credit: Aladin at SIMBAD.{{free media}}

A subgiant star is a star that is slightly brighter than a normal main-sequence (dwarf) star of the same spectral class, but not as bright as true giant stars. Although certain subgiants appear to be simply unusually bright metal-rich hydrogen-fusing stars (in the same way subdwarfs are unusually dim metal-poor hydrogen-fusing stars), they are generally believed to be stars that are ceasing or have already ceased fusing hydrogen in their cores.

Many subgiants are rich in metals, and commonly host orbiting planets.

At right is a visual image in close to true color of V972 Scorpii, which is a variable star of the delta Sct type. It has spectral type G2IV and is a star in a cluster. The system includes components CCDM J16234-2622 A and CCDM J16234-2622 B. Component A is a dwarf star in a double star system with component B. Component A is apparently V972 Scuti.

Yellow giantsEdit

Alpha Microscopii is a spectral type G7III yellow giant star in a double system. Credit: Aladin at SIMBAD.{{free media}}

Alpha Microscopii is a spectral type G7III yellow giant star in a double system.

This star has an optical visual companion, CCDM J20500-3347B, of apparent visual magnitude 10.0 approximately 20.4 arcseconds away at a position angle of 166°. It has no physical connection to the star described above.[74]

Barium starsEdit

Barium stars are spectral class G to K giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2.

Observational studies of their radial velocity suggested that all barium stars are binary stars[75][76][77] Observations in the ultraviolet using the International Ultraviolet Explorer detected white dwarfs in some barium star systems.

Barium stars are believed to be the result of mass transfer in a binary star system. The mass transfer occurred when the presently-observed giant star was on the main sequence. Its companion, the donor star, was a carbon star on the asymptotic giant branch (AGB), and had produced carbon and s-process elements in its interior. These nuclear fusion products were mixed by convection to its surface. Some of that matter "polluted" the surface layers of the main sequence star as the donor star lost mass at the end of its AGB evolution, and it subsequently evolved to become a white dwarf. We are observing these systems an indeterminate amount of time after the mass transfer event, when the donor star has long been a white dwarf, and the "polluted" recipient star has evolved to become a red giant.[78][79]

Barium stars exhibit carbon and s-process elements at their surfaces suggesting surface fusion possible during mass transfer or without it.

The mass transfer hypothesis predicts that there should be main sequence stars with barium star spectral peculiarities. At least one such star, HR 107, is known.[80]

Prototypical barium stars include zeta Capricorni, HR 774, and HR 4474.

Yellow supergiantsEdit

V781 Cas was imaged by SDSS. Credit: SDSS.{{free media}}

A yellow supergiant (YSG) is a supergiant star of spectral type F or G.[81] These stars usually have masses between 15 and 20 solar masses. These stars, like any other supergiant, are older and swing between blue and red phases depending on the chemical elements they consume in their cores. Until now it had been thought that few supergiants spend a long time in the transitional yellow phase. These systems may be the progenitors of rare supernovae linked to yellow supergiants. Only [a] few such supernovae have been detected - most supergiants go supernova when at the blue (or hot) phase or red (or cool) phase.

DY Persei variablesEdit

DY Persei is shown in optical light. Credit: David Ritter.{{free media}}
Light curve of DY Persei from 2014 to 2017 was created using the AAVSO light curve generator tool. Credit: Lithopsian.{{free media}}

DY Persei variables are a subclass of R Coronae Borealis variables. They are carbon-rich asymptotic giant branch stars that exhibit pulsational variability of AGB stars and irregular variability of RCB stars.

The star DY Persei is the prototype of this tiny class of variable stars.

DY Persei in the Perseus constellation pulsates like red variables, ... [and fades] from sight like R Coronae Borealis variables.

R Coronae Borealis variableEdit

The graph is of an AAVSO light curve of fadings by R Coronae Borealis, the prototype star. Credit: Jimstars.{{fairuse}}

An R Coronae Borealis variable (abbreviated RCB) is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation (a few tenths of a magnitude), and one irregular unpredictably sudden fading by 1 to 9 magnitudes.

The prototype star [is] R Coronae Borealis ... [O]nly about 100 RCB variables have been identified,[82] making this class a very rare kind of star.

The fading is caused by condensation of carbon to soot, making the star fade in visible light while measurements in infrared light exhibit no real luminosity decrease. R Coronae Borealis variables are typically supergiant stars in the spectral classes F and G (by convention called "yellow"), with typical C2 and CN molecular bands, characteristic of yellow supergiants. RCB star atmospheres do however lack hydrogen by an abundance of 1 part per 1,000 down to 1 part per 1,000,000 relative to helium and other chemical elements, while the universal abundance of hydrogen is about 3 to 1 relative to helium.

There is a considerable variation in spectrum between various RCB specimens. Most of the stars with known spectrum are either F to G class ("yellow") supergiants, or a comparatively cooler C-R type carbon star supergiant. Three of the stars are however of the "blue" B type, for example VZ Sagittarii, and one is a "red" giant star, V482 Cygni of type M5III. Four stars are unusually and inexplicably poor in iron absorption lines in the spectrum.[83] The constant features are prominent Carbon lines, strong atmospheric Hydrogen deficiencies, and obviously the intermittent fadings.

Yellow hypergiantsEdit

Rho Cassiopeiae is a semi-regular pulsating star of spectral class G2Ia0e. Credit: Aladin at SIMBAD.{{fairuse}}

"ρ Cas, HR 8752 and IRC+10420, three well-studied yellow hypergiants, are situated at or close to the red border of the [yellow evolutionary] void."[84]

Generally speaking, a yellow hypergiant is a massive star with an extended atmosphere, which can be classified as spectral class from late A to K, with a mass of as much as 20-50 solar masses. Yellow hypergiants, such as Rho Cassiopeiae in the constellation Cassiopeia, have been observed to experience periodic eruptions, resulting in periodic or continuous dimming of the star, respectively. Yellow hypergiants appear to be extremely rare in the universe. Due to their extremely rapid rate of consumption of nuclear fuel, yellow hypergiants generally only remain on the main sequence for a few million years before destroying themselves in a massive supernova or hypernova. Yellow hypergiants are post-red supergiants, rapidly evolving toward the blue supergiant phase.

According to the current physical models of stars, a yellow hypergiant should possess a convective core surrounded by a radiative zone, as opposed to a sun-sized star, which consists of a radiative core surrounded by a convective zone (Seeds, 2005). Due to the extremely high pressures which exist at the core of a yellow hypergiant, portions of the core or perhaps the entire core may be composed of degenerate matter.

These stars have powerful magnetic fields.

Yellow evolutionary voidEdit

G is host to the "Yellow Evolutionary Void".[84] Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be.

"[T]he yellow evolutionary void ... is an area in the Hertzspung-Russell diagram where atmospheres of blueward evolving super- and hypergiants are moderately unstable ... For [such stars] (in hydrostatic equilibrium)

  1. a negative density gradient occurs,
  2. the sum of all accelerations, including wind, turbulence and pulsations, is zero or negative,
  3. the sonic point of the stellar wind is reached in or below photospheric levels, and
  4. Γ1 ≤ 4/3 indicating some level of dynamic instability in part of the atmosphere."[84]

Yellow galaxiesEdit

This image shows a cluster of yellow galaxies near the middle of the photograph. Credit: STScl/NASA.{{free media}}

The image at right shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.


  1. Each of the planets revolving around Sol can be seen in the yellow.

See alsoEdit


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Further readingEdit

External linksEdit

{{Radiation astronomy resources}}