Radiation astronomy/Colors

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This is a cross section of HSL color space. Credit: MaxPower.

Each form of radiation that an astronomical entity can emit, absorb, fluoresce, transmit, or reflect has a spectrum in time, space, intensity, or variation.

A spectrum of variation shows its colors.


Main source: Astronomy

Astronomy in general consists of observing the types of spectra apparently originating with an astronomical entity and describing these observations empirically if necessary with theory.


Main source: Radiation

Radiation in its spectrum of forms from meteors to Superluminals shows variation, time, space, and intensity.


Main source: Minerals
This image exhibits forty-seven minerals that fluoresce in the visible while being irradiated in the ultraviolet. Credit: Hannes Grobe Hgrobe.
Fluorescing fluorite is from Boltsburn Mine Weardale, North Pennines, County Durham, England, UK. Credit: .
Calcite fluoresces pink under long wave ultraviolet light. Credit: .
Calcite fluoresces blue under short wave ultraviolet light. Credit: .

"Ultraviolet lamps are also used in analyzing minerals and gems, ... Materials may look the same under visible light, but fluoresce to different degrees under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet."[1]

"Ultraviolet lamps may cause certain minerals to fluoresce, and is a key tool in prospecting for tungsten mineralisation."[2]

"Many samples of fluorite exhibit fluorescence under ultraviolet light, a property that takes its name from fluorite.[3] Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green and white also occur. The fluorescence of fluorite may be due to mineral impurities such as yttrium, ytterbium, or organic matter in the crystal lattice. In particular, the blue fluorescence seen in fluorites from certain parts of Great Britain responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent europium in the crystal.[4]"[5]

"Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4.[6]"[7]

"Under longwave (365 nm) ultraviolet light, diamond may fluoresce a blue, yellow, green, mauve, or red of varying intensity. The most common fluorescence is blue, and such stones may also phosphoresce yellow—this is thought to be a unique combination among gemstones. There is usually little if any response to shortwave ultraviolet".[8]


This ultraviolet-wavelength image mosaic, taken by NASA's Galaxy Evolution Explorer (GALEX), shows a comet-like "tail" stretching 13 light years across space. Credit: NASA.
This image shows a late-summer rainstorm in Denmark. The nearly black color of the cloud's base indicates the foreground cloud is probably cumulonimbus. Credit: Malene Thyssen.
This is a panorama photograph taken during a lightning storm over Bucharest, Romania. Credit: Catalin.Fatu.
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.
Comet West is photographed on March 6, 2006. Credit: Jlsmicro.
Visual photograph of Comet West in early March 1976 shows red gases coming off the comet's head and multicolor dust tail. Credit: Peter Stättmayer (Munich Public Observatory) and ESO.
McNaught Comet is captured in visual color with a Canon 350D...EF50...F2...25 sec. Credit: Davewhite7.
This is a photograph taken in 1910 during the passage of Halley's comet. Credit: The Yerkes Observatory.
The volcanic eruption from Mount Pinatubo deposits a snowlike blanket of tephra on June 15, 1991. Credit: R.P. Hoblitt, USGS.
Here at Réunion is an example that some of those white puffy objects in the sky may be quite close by. Credit: B.navez.
Cirrus clouds never seem to touch any mountain. Yet sunrise reveals they are closer to the ground than the Sun. Credit: Simon Eugster.
The telescope photograph of the Great Andromeda Nebula is taken around 1899. Credit: Isaac Roberts.

A spectrum of meteors may range in size (space), speed (time), numbers (intensity), or state (variation, e.g. rocky, liquid, gaseous, or plasma).

"The 1910 approach, which came into naked-eye view around 10 April[9] and came to perihelion on 20 April,[9] was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained.[10] Furthermore, the comet made a relatively close approach of 0.15AU,[9] making it a spectacular sight. Indeed, on 19 May, the Earth actually passed through the tail of the comet.[11][12] One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen,[13] which led astronomer Camille Flammarion to claim that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet."[14] His pronouncement led to panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.[15] In reality, as other astronomers were quick to point out, the gas is so diffuse that the world suffered no ill effects from the passage through the tail.[14]"[16]

"It is quite possible that [faint streamers preceding the main tail and lying nearly in the prolonged radius vector] may have touched the Earth, probably between May 19.0 and May 19.5, [1910,] but the Earth must have passed considerably to the south of the main portion of the tail [of Halley's comet]."[17]

"A typical comet nucleus has an albedo of 0.04.[18]"[19]

At left is an image of Comet West. "Comet West was a stunning sight in the predawn sky of March, 1976, bright with a tall and broad dust tail. ... [T]he comet [was] discovered on photographs taken in August 1975 by Richard West of the European Southern Observatory ... Comet West passed perihelion on February 25, 1976, at a distance of 0.20 a.u. [and] had reached about magnitude -3 at perihelion. Several observers saw it telescopically in daylight, and John Bortle observed it with the naked eye shortly before sunset. ... The following morning, March 7, ... It was brilliant, with a head as bright as Vega (which was nearly overhead) and a huge tail, about 20 degrees tall, straight near the bottom and bending to the left in its upper reaches. The comet quickly faded during March".[20]

Although many comets are photographed in black and white, not that many are actually only white but have colors. The image at right of McNaught Comet shows white and other colors, as does Comet West at left.

Of the Local Group, “[i]ts two dominant galaxies, the Milky Way and Andromeda (M31), are separated by a distance of ~700 kpc and are moving toward each other with a radial velocity of about -117 km s-1 (Binney & Tremaine 1987, p. 605).”[21] "making [Andromeda] one of the few blueshifted galaxies. The Andromeda Galaxy and the Milky Way are thus expected to collide in about 4.5 billion years, although the details are uncertain since Andromeda's tangential velocity with respect to the Milky Way is only known to within about a factor of two.[22] A likely outcome of the collision is that the galaxies will merge to form a giant elliptical galaxy.[23] Such events are frequent among the galaxies in galaxy groups. The fate of the Earth and the Solar System in the event of a collision are currently unknown. If the galaxies do not merge, there is a small chance that the Solar System could be ejected from the Milky Way or join Andromeda.[24]"[25]

Cosmic rays[edit]

The flux of cosmic-ray particles is a function of their energy. Credit: Sven Lafebre, after Swordy.[26]

At right is an image indicating the range of cosmic-ray energies. The flux for the lowest energies (yellow zone) is mainly attributed to solar cosmic rays, intermediate energies (blue) to galactic cosmic rays, and highest energies (purple) to extragalactic cosmic rays.[26]

Cosmic rays may be upwards of a ZeV (1021 eV).

“About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei of alpha particles, and 1% are the nuclei of heavier elements. ... Solitary electrons ... constitute much of the remaining 1%.”[27]


"The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature. The neutron energy distribution is then adopted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the kinetic energy is of the free neutron. Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation."[28]

"Moderated and other, non-thermal neutron energy distributions or ranges are ...

  • Fast neutrons [with] kinetic energies greater than 1 eV, 0.1 MeV or approximately 1 MeV, depending on the definition.
  • Slow neutrons ... a kinetic energy less than or equal to 0.4 eV.
  • Epithermal neutrons ... an energy from 1 eV to 10 keV.
  • Hot neutrons ... an energy of about 0.2 eV.
  • Thermal neutrons ... an energy of about 0.025 eV.[29] This is the most probable energy, while the average energy is 0.038 eV.
  • Cold neutrons ... an energy from 5 × 10−5 eV to 0.025 eV.
  • Very cold neutrons ... an energy from 3 × 10−7 eV to 5 × 10−5 eV.
  • Ultra cold neutrons ... an energy less than 3 × 10−7 eV.
  • Continuum region neutrons ... an energy from 0.01 MeV to 25 MeV.
  • Resonance region neutrons ... an energy from 1 eV to 0.01 MeV.
  • Low energy region neutrons ... an energy less than 1 eV."[28]


Notation: WN5 is a component of V444 Cygni, with its Wolf-Rayet (W) spectrum dominated by NitrogenIII-V and HeliumI-II lines and WN2 to WN5 considered hotter or "early".

"The color temperature of the central part of the WN5 disk for λ < 7512 Å, where the main source of opacity is electron scattering, is Tc = 80,000-100,000 K. This high temperature represents the electron temperature slightly below the surface of the WN5 core--the level at which the star becomes optically thick in electron scattering."[30]


This is an image obtained from muon radiography of Japan's Asama volcano. Credit: H T M Tanaka.

The colors chosen for the image on the right relate to density of the rock.


Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo[31] whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates. Neutrino oscillation is of theoretical and experimental interest since observation of the phenomenon implies that the neutrino has a non-zero mass”.[32]


Sample calibration colors[33]
Class B–V U–B V–R R–I Teff (K)
O5V –0.33 –1.19 –0.15 –0.32 42,000
B0V –0.30 –1.08 –0.13 –0.29 30,000
A0V –0.02 –0.02 0.02 –0.02 9,790
F0V 0.30 0.03 0.30 0.17 7,300
G0V 0.58 0.06 0.50 0.31 5,940
K0V 0.81 0.45 0.64 0.42 5,150
M0V 1.40 1.22 1.28 0.91 3,840

"[T]he color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. To measure the index, one observes the magnitude of an object successively through two different filters, such as U and B, or B and V, where U is sensitive to ultraviolet rays, B is sensitive to blue light, and V is sensitive to visible (green-yellow) light (see also: UBV system). The set of passbands or filters is called a photometric system. The difference in magnitudes found with these filters is called the U-B or B–V color index, respectively. The smaller the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is. This is a consequence of the logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the yellowish Sun has a B–V index of 0.656 ± 0.005,[34] while the bluish Rigel has B–V –0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B–V = –0.03).[35] The passbands most optical astronomers use are the UBVRI filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes infrared light. ... These filters were specified as particular combinations of glass filters and photomultiplier tubes."[36]

"[A] Photometric system is a set of well-defined passbands (or filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided."[37]

Filter Letter Effective Wavelength Midpoint λeff For Standard Filter[38] Full Width Half Maximum[38] Variant(s) Description
U 365nm 66nm u, u', u* "U" stands for ultraviolet.
B 445nm 94nm b "B" stands for blue.
V 551nm 88nm v, v' "V" stands for visual.
G g, g' "G" stands for green (visual).
R 658nm 138nm r, r', R', Rc, Re, Rj "R" stands for red.
I 806nm 149nm i, i', Ic, Ie, Ij "I" stands for infrared.


These are the various shades of gray. Credit: Mizunoryu, Badseed, Jacobolus.
This image shows some red pebbles among gray pebbles of the same rock type. Credit: Titus Tscharntke.

"Grey or gray is an intermediate color between black and white, a neutral or achromatic color, meaning literally a color "without color." [39] It is the color of a cloud-covered sky, of ash and of lead.[40]"[41]

The first image at right shows some red pebbles among gray pebbles, which are all the same rock type.

The first image at left shows the various shades of grey.

These white cliffs of Dover are made of chalk, or calcium carbonate. Credit: Remi Jouan.
Cumulus clouds in fair weather are white. Credit: Michael Jastremski.

"White is the color of fresh milk and snow.[42][43] It is the color the human eye sees when it looks at light which contains all the wavelengths of the visible spectrum, at full brightness and without absorption. It does not have any hue.[44]"[45]

"de la couleur de la neige, du lait. Lumiere resultant de la combinaison de toutes les couleurs du spectre solaire."[46] (of the color of snow, of milk. Light resulting from the combination of all the colors of the solar spectrum.)

The white cliffs shown in the image at right are made of chalk, or calcium carbonate.

"[W]hite light reflected off objects can be seen when no part of the light spectrum is reflected significantly more than any other and the reflecting material has a degree of diffusion. People see this when transparent fibers, particles, or droplets are in a transparent matrix of a substantially different refractive index. Examples include classic "white" substances such as sugar, foam, pure sand or snow, cotton, clouds, and milk. Crystal boundaries and imperfections can also make otherwise transparent materials white, as in the milky quartz or the microcrystalline structure of a seashell."[45]

"Cumulus clouds look white because the water droplets reflect and scatter the sunlight without absorbing other colors."[45]

"White light is generated by the sun, by stars, or by earthbound sources such as incandescent lamps, fluorescent lamps and white LEDs."[45]

Anthracite coal is black. Credit: USGS and the Mineral Information Institute.
Basalt is a black rock, albite is a white mineral silicate, and epidote is green. Credit: Siim Sepp.

"Black is the color of coal, ebony, and of outer space. It is the darkest color, the result of the absence of or complete absorption of light. It is the opposite of white and often represents darkness in contrast with light.[47][48][49]"[50]

"Opposite to white: colourless from the absence or complete absorption of light. Also, so near this as to have no distinguishable colour, very dark."[47]

Black is "[t]he darkest color".[48]

"Se dit de la couleur la plus foncée, due à l'absence ou à l'absorption totale des rayons lumineux."[49]("said of the very darkest color, due to the absence or complete absorption of all rays of light.")

sRGB rendering of the spectrum of visible light
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

"The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm.[51] In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function)."[52]

There are several cases of astronomers who claimed that following a cataract operation, they could see shorter wavelengths than other people, slightly into the ultraviolet.


Various shades of violet are shown. Credit: Mizunoryu, Badseed, Jacobolus.
Variations of violet are shown. Credit: Badseed.
The diagram shows various shades of purple. Credit: Mizunoryu, Badseed, Jacobolus.

Def. “[a] bluish-purple colour"[53] is called violet.

Def. “[a] colour/color that is a dark blend of red and blue; dark magenta"[54] is called purple.

"Purple is a range of hues of color occurring between red and blue.[55] The Oxford English Dictionary describes it as a deep, rich shade between crimson and violet.[56]"[57]


These are various shades of blue. Credit: Booyabazooka.
Blue, green and red are additive colors. All the colors you see on your computer screen are made by mixing them in different intensities. Credit: Bb3cxv.

"Blue is the colour of the clear sky and the deep sea.[58]"[59]

"De la couleur du ciel sans nuages, de l'azur"[60]


The color box shows some of the variations of cyan. Credit: .

Electric blue is a color close to cyan that is a representation of the color of lightning, an electric spark, and argon signs”.[61]

“The electric blue glow of electricity results from the spectral emission of the excited ionized atoms (or excited molecules) of air (mostly oxygen and nitrogen) falling back to unexcited states, which happens to produce an abundance of electric blue light. This is the reason electrical sparks in air, including lightning, appear electric blue. It is a coincidence that the color of Cherenkov radiation and light emitted by ionized air are a very similar blue despite their very different methods of production.”[61]

"Aero blue is a fluorescent cyan color."[62]

"The word [cerulean] is probably derived from the Latin word caeruleus, "dark blue, blue or blue-green", which in turn probably derives from caelulum, diminutive of caelum, "heaven, sky".[63]"[62]

"Natural gas (methane) [...] has a cyan colored flame when burned with a mixture of air."[64]


These color squares show a variety of greens. Credit: FedericoMP.
Green, blue and red are additive colors. All the colors you see on your computer screen are made by mixing them in different intensities. Credit: Bb3cxv.
The word green has the same Germanic root as the words for grass and grow and is a common color reflected by leaves on Earth. Credit: The cat.
Malachite is a mineral occurring on Earth, like many greens, is colored by the presence of copper, specifically by basic copper(II) carbonate.[65] Credit: Rob Lavinsky.

Green has a wavelength range of approximately 520–570 nm,[66] a frequency range of ~575–525 THz,[66] with color coordinates of (0, 255, 0) and a hexagonal triplet of #00FF00 from sRGB source of sRGB approximation to NCS S 2060-G.[67]

Def. "[t]he colour of growing foliage, as well as other plant cells containing chlorophyll; the colour between yellow and blue in the visible spectrum; one of the primary additive colour for transmitted light; the colour obtained by subtracting red and blue from white light using cyan and yellow filters"[68] is called green.

"...in nature chiefly conspicuous as the colour of growing herbage and leaves..."[69]

"Green is the color of emeralds, jade, and growing grass.[69] In the continuum of colors of visible light it is located between yellow and blue. Green is the color most commonly associated with nature and the environmental movement, Islam, spring, hope and envy.[70]"[66]

"Green is the color you see when you look at light with a wavelength of roughly 520–570 nanometers."[66]

"It is one of the three additive colors, along with red and blue, which are combined on computer screens and color televisions to make all other colors."[66]

"In the subtractive color system, used in printing, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan."[66]

"On the HSV color wheel, also known as the RGB color wheel, the complement of green is magenta; that is, a purple color corresponding to an equal mixture of red and blue light. On a color wheel based on traditional color theory (RYB), the complementary color to green is considered to be red.[71]"[66]

"The perception of greenness (in opposition to redness forming one of the opponent mechanisms in human color vision) is evoked by light which triggers the medium-wavelength M cone cells in the eye more than the long-wavelength L cones. Light which triggers this greenness response more than the yellowness or blueness of the other color opponent mechanism is called green. A green light source typically has a spectral power distribution dominated by energy with a wavelength of roughly 487–570 nm. More specifically, "blue green" 487–493 nm, "bluish green" 493–498 nm, "green" 498–530 nm, "yellowish green" 530–559 nm, "yellow green" 559–570 nm.[72]"[66]

"Green earth is a natural pigment ... It s composed of clay colored by iron oxide, magnesium, aluminum silicate, or potassium. Large deposits were found in the South of France near Nice, and in Italy around Verona, on Cyprus, and in Bohemia. The clay was crushed, washed to remove impurities, then powdered. It was sometimes called Green of Verona.[73]"[66]


These are examples of the various colors of yellow. Credit: Badseed.
Complements of yellow have a dominant wavelength in the range 380 to 480 nm. The green lines show several possible pairs of complementary colors. Credit: .
The image is of a horse colored with yellow ochre. from Lascaux cave. Credit: Cro-Magnon peoples.
This shows a field of yellow rapeseed. Credit: Petr Kratochvil.

Def. "[t]he colour of gold or butter; the colour obtained by mixing green and red light, or by subtracting blue from white light"[74] is called yellow.

Def. a "bright yellow colour, resembling the metal gold"[75]

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."[76]

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


The box shows nine variations of the color orange. Credit: .

Def. "[t]he colour of a ripe orange (the fruit); a color midway between red and yellow"[77] is called orange.


In wavelengths, red astronomy covers 620 - 750 nm.

"Infrared or red radiation from a common household radiator or electric heater is an example of thermal radiation, as is the heat emitted by an operating incandescent light bulb. Thermal radiation is generated when energy from the movement of charged particles within atoms is converted to electromagnetic radiation."[78]

"Infrared (IR) light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometres (nm) to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz,[79] and includes most of the thermal radiation emitted by objects near room temperature. Infrared light is emitted or absorbed by molecules when they change their rotational-vibrational movements."[80]

"Far-red light is light at the extreme red end of the visible spectrum, between red and infra-red light. Usually regarded as the region between 710 and 850 nm wavelength, it is dimly visible to some [human] eyes."[81]


Aurorae are mostly caused by energetic electrons precipitating into the atmosphere.[82] Credit: Samuel Blanc[1].

"Electron temperatures are generally derived from the ratio of auroral to nebular lines in [O III] or [N II]."[83] "[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."[83]

Coronal clouds[edit]

"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."[84]

"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 yellow line emission (λ 5694)."[84]

"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."[84]

"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."[84]


"[B]roadband optical photometry of Centaurs and Kuiper Belt objects [KBOs] from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."[85]

Kuiper belts[edit]

Main source: Kuiper belts

"These authors proposed that the whole-disk surface colors of KBOs could be the result of the competition between the effects of irradiation of surface organics by cosmic-rays and the global resurfacing due to impacts. [...] When these high-energy protons collide with an icy target, they penetrate very [deep] under the surface."[86]


Main source: Hypotheses
  1. The orthogonality between electric fields and magnetic fields came before 3D space.
  2. Orthogonality between electric fields and magnetic fields creates the illusion of three-dimensional space.
  3. Interference interactions create attractions and repulsions between fields which in turn produces radiance, motion, and allows time to be calibrated.
  4. Interactions create segmentation yielding an apparent particle/wave duality.

See also[edit]


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  7. "Calcite, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. June 20, 2013. Retrieved 2013-06-30. 
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  9. 9.0 9.1 9.2 D. K. Yeomans (1998). "Great Comets in History". Jet Propulsion Laboratory. Retrieved 15 March 2007. 
  10. D. A. Mendis (1988). "A Postencounter view of comets". Annual Review of Astronomy and Astrophysics 26 (1): 11–49. doi:10.1146/annurev.aa.26.090188.000303. 
  11. Ian Ridpath (1985). "Through the comet’s tail". Revised extracts from A Comet Called Halley by Ian Ridpath, published by Cambridge University Press in 1985. Retrieved 2011-06-19. 
  12. Brian Nunnally (May 16, 2011). "This Week in Science History: Halley’s Comet". pfizer: ThinkScience Now. Retrieved 2011-06-19. 
  13. "Yerkes Observatory Finds Cyanogen in Spectrum of Halley's Comet". The New York Times. 8 February 1910. Retrieved 15 November 2009. 
  14. 14.0 14.1 "Ten Notable Apocalypses That (Obviously) Didn't Happen". Smithsonian magazine. 2009. Retrieved 14 November 2009. 
  15. "Interesting Facts About Comets". Universe Today. 2009. Retrieved 15 January 2009. 
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  22. The Grand Collision, from the series: The Sky At Night, airdate: November 5, 2007
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  24. Cain, F. (2007). "When Our Galaxy Smashes Into Andromeda, What Happens to the Sun?". Universe Today. Retrieved 2007-05-16. 
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