Radiation astronomy/Sources

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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}}

Radiation astronomy sources, or radiation sources, are entities or objects from which radiation comes or is acquired.

"What is the source of the radiation?" is the question.

Each form of radiation is usually associated with a magnitude of energy for origination.

The phenomenon of radiation is consistent with a point of origin of a ray, beam, or stream of small cross section traveling approximately in a line.

The sky, or sometimes the heavens, is apparently impenetrable to some forms of radiation, transparent to others, and translucent to the rest.

Theoretical radiation sources[edit | edit source]

Def. the point, area, or region of origin of a ray, beam, or stream of small cross section traveling in a line is called a radiation source.

Def. a natural source usually of radiation in the sky especially at night is called an astronomical source.

Primary sources[edit | edit source]

Sources, or apparent sources, detected or created at or near the time of the event or events are primary sources.

Secondary sources[edit | edit source]

Sources, or apparent sources, that transform or transduce anything originating from primary sources are secondary sources.

Tertiary sources[edit | edit source]

Sources, or apparent sources, that select, distill, scatter, or reflect anything from primary or secondary sources are tertiary sources.

Meteor showers[edit | edit source]

A Perseid meteor streaks through above the clouds. Credit: John Fowler from Placitas, NM, USA.{{free media}}
Perseid meteor traces demonstrating their radiant source. Credit: Unknown.{{free media}}

Of some 670 Perseids examined for colors from 1985, 1988, and 1989, 128 were blue meteors, 3 were multi-colored yellow-blue and one was blue-green [cyan].[1] The average pre-atmospheric velocity is 59.9 km/s.[1]

The Perseids are a prolific meteor shower associated with the comet Swift-Tuttle. The Perseids are so-called because the point from which they appear to come, called the radiant, lies in the constellation Perseus.

Gamma rays[edit | edit source]

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

The Rosemary Hill Observatory (RHO) started observing 3C 279 in 1971,[2] and was further observed by the Compton Gamma Ray Observatory in 1991, when it was unexpectedly discovered to be one of the brightest gamma ray objects in the sky.[3] It is also one of the most bright and variable sources in the gamma ray sky monitored by the Fermi Space Telescope. Apparent superluminal motion was detected during observations first made in 1973 in a jet of material departing from the quasar, though it should be understood that this effect is an optical illusion caused by naive estimations of the speed, and no truly superluminal motion is occurring.[4]

X-rays[edit | edit source]

Def. a natural source usually of X-rays (X-radiation) in the sky especially at night is called an astronomical X-ray source.

The apparent source may be reflecting, generating and emitting, transmitting, or fluorescing X-rays which may be detectable.

"Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus, the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere."[5]

Serpens X-1[edit | edit source]

Serpens X-1 is an X-ray source with an error circle fixed for all time on the celestial sphere. It is also an X-ray entity in the sense that it has an "independent, separate, or self-contained astronomical existence." from theoretical astronomy. It has a history, a spatial extent, and a spectral extent.

Solar coronal cloud[edit | edit source]

This image shows the Sun as viewed by the Soft X-Ray Telescope (SXT) onboard the orbiting Yohkoh satellite. Credit: NASA Goddard Laboratory for Atmospheres.{{fairuse}}

Although a coronal cloud (as part or all of a stellar or galactic corona) is usually "filled with high-temperature plasma at temperatures of T ≈ 1–2 (MK), ... [h]ot active regions and postflare loops have plasma temperatures of T ≈ 2–40 MK."[6]

In the image at right, the photosphere of the Sun is dark in X-rays. However, apparently associated with the Sun is a high-temperature plasma that radiates in X-rays at temperatures 1,000 times as hot as the photosphere.

Super soft X-ray sources[edit | edit source]

A super soft X-ray source (SSXS, or SSS) is an astronomical source of very low energy X-rays. Soft X-rays have energies in the 0.09 to 2.5 keV range, whereas hard X-rays are in the 1-20 keV range.[7]

Super soft X-ray sources (SSXSs) are in most cases only detected below 0.5 keV, so that within our own galaxy they are usually hidden by interstellar absorption in the galactic disk.[8] They are readily evident in external galaxies, with ~10 found in the Magellanic Clouds and at least 15 seen in M31.[8]

Ultraluminous X-rays[edit | edit source]

This is a composite image (X-ray - red, optical - blue & white) of the spiral galaxy M74 with an ultraluminous X-ray source (ULX) indicated inside the box. Image is 9 arcmin per side at RA 01h 36m 41.70s Dec +15° 46' 59.0" in Pisces. Observation dates: June 19, 2001; October 19, 2001. Aka: NGC 628, ULX: CXOU J013651.1+154547. Credit: X-ray; J. Liu (U.Mich.) et al., CXC, NASA - Optical; Todd Boroson/NOAO/AURA/NSF.{{fairuse}}

Ultraluminous X-ray sources (ULXs) are pointlike, nonnuclear X-ray sources with luminosities above the Eddington limit of 3 × 1039 ergs s−1 for a 20 Mʘ black hole.[9] Many ULXs show strong variability and may be black hole binaries. To fall into the class of intermediate-mass black holes (IMBHs), their luminosities, thermal disk emissions, variation timescales, and surrounding emission-line nebulae must suggest this.[9] However, when the emission is beamed or exceeds the Eddington limit, the ULX may be a stellar-mass black hole.[9] The nearby spiral galaxy NGC 1313 has two compact ULXs, X-1 and X-2. For X-1 the X-ray luminosity increases to a maximum of 3 × 1040 ergs s−1, exceeding the Eddington limit, and enters a steep power-law state at high luminosities more indicative of a stellar-mass black hole, whereas X-2 has the opposite behavior and appears to be in the hard X-ray state of an IMBH.[9]

The X-ray/optical composite at right "highlights an ultraluminous X-ray source (ULX) shown in the box. ... The timing and regularity of these outbursts ... make the object one of the best candidates yet for a so-called intermediate-mass black hole. ... Chandra X-ray Observatory observations of this ULX have provided evidence that its X-radiation is produced by a disk of hot gas swirling around a black hole with a mass of about 10,000 suns."[10] "Chandra observed M74 twice: once in June 2001 and again in October 2001. The XMM-Newton satellite also (a European Space Agency mission) observed this object in February 2002 and January 2003."[10]

Ultraviolets[edit | edit source]

STEREO—First images is a slow animation of a mosaic of the extreme ultraviolet images taken on December 4, 2006. These false color images show the Sun's atmospheres at a range of different temperatures. Clockwise from top left: 1 million degrees C (171 Å—blue), 1.5 million °C (195 Å—green), 60,000–80,000 °C (304 Å—red), and 2.5 million °C (286 Å—yellow). Credit: NASA.{{free media}}
This image of the Sun is taken on December 16, 2008, during sunspot-minimum conditions, using light produced at a wavelength of 19.5 nanometers by the ion Fe XII. Credit: NASA/ESA, SOHO/EIT.{{fairuse}}

In the corona thermal conduction occurs from the external hotter atmosphere towards the inner cooler layers. Responsible for the diffusion process of the heat are the electrons, which are much lighter than ions and move faster.

Ultraviolet telescopes such as TRACE and SOHO/EIT can observe individual micro-flares as small brightenings in extreme ultraviolet light,[11] but there seem to be too few of these small events to account for the energy released into the corona.

The first direct observation of waves propagating into and through the solar corona was made in 1997 with the SOHO space-borne solar observatory, the first platform capable of observing the Sun in the extreme ultraviolet (EUV) for long periods of time with stable photometry. Those were magneto-acoustic waves with a frequency of about 1 millihertz (mHz, corresponding to a 1,000 second wave period), that carry only about 10% of the energy required to heat the corona. Many observations exist of localized wave phenomena, such as Alfvén waves launched by solar flares, but those events are transient and cannot explain the uniform coronal heat.

"Ultraviolet irradiance (EUV) varies by approximately 1.5 percent from solar maxima to minima, for 200 to 300 nm UV.[12]

"1 percent of the sun's energy is emitted at ultraviolet wavelengths between 200 and 300 nanometers, the decrease in this radiation from 1 July 1981 to 30 June 1985 accounted for 19 percent of the decrease in the total irradiance".[12]

Energy changes in the UV wavelengths involved in production and loss of ozone have atmospheric effects.

The 30 hPa atmospheric pressure level has changed height in phase with solar activity during the last 4 solar cycles.

UV irradiance increase causes higher ozone production, leading to stratospheric heating and to poleward displacements in the stratospheric and tropospheric wind systems.

A proxy study estimates that UV has increased by 3.0% since the Maunder Minimum.[13]

"Solar satellite observatories such as ESA/NASA's Solar and Heliospheric Observatory (SOHO) have been studying the sun for over 10 years, and have created images of the entire solar surface using spectroscopic techniques. [The second image at right] shows a recent full-sun image created by the Extreme-ultraviolet Imaging Telescope (EIT) taken during sunspot-minimum conditions in 2008. [...] By using the techniques of imaging spectroscopy, solar physicists can isolate gases heated to temperatures of 1,500,000 K and study their motions and evolution over time."[14]

The second image at right is "taken on December 16, 2008 during sunspot-minimum conditions, was created by isolating the light produced at a wavelength of 195 Angstroms (19.5 nanometers) by the ion Fe XII. By selecting the light from only one spectral line, a spectroheliograph works like a high-precision light filter and lets astronomers map, or image, a distant object in the light from a single spectral line. This information can be used to map the temperature and density changes in the gas."[14]

Opticals[edit | edit source]

This is an image of the star-forming region R136 in NGC 2070 with the Hubble Space Telescope in ultraviolet and visible light. Credit: NASA, ESA, F. Paresce (INAF-IASF, Bologna, Italy), R. O'Connell (University of Virginia, Charlottesville), and the Wide Field Camera 3 Science Oversight Committee.{{free media}}

Ultraviolet astronomy is radiation astronomy applied to the ultraviolet phenomena of the sky, 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) ultraviolet astronomy.

In ultraviolet-optical astronomy, images may yield important information. The image at right "is the most detailed view of the largest stellar nursery in our local galactic neighborhood. The massive, young stellar grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. There is no known star-forming region in our galaxy as large or as prolific as 30 Doradus. Many of the diamond-like icy blue stars are among the most massive stars known. Several of them are over 100 times more massive than our Sun. These hefty stars are destined to pop off, like a string of firecrackers, as supernovas in a few million years. This image, taken in ultraviolet, visible, and red light by Hubble's Wide Field Camera 3, spans about 100 light-years. The nebula is close enough to Earth that Hubble can resolve individual stars, giving astronomers important information about the birth and evolution of stars in the universe. The Hubble observations were taken Oct. 20-27, 2009. The blue color is light from the hottest, most massive stars; the green from the glow of oxygen; and the red from fluorescing hydrogen."[15]

Visuals[edit | edit source]

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

There are yellow objects and emission lines in the yellow portion of the visible spectrum to introduce yellow astronomy.

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.[16] "The coronal temperature was 4000000°."[16] "The December 18, 1956, flare appears to have been a violent condensation of material from a dense coronal cloud above an active region."[16]

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.

Violets[edit | edit source]

This is a colour-composite of the barred spiral galaxy NGC 5584. Credit: ESO: observations by Susana Randall, Claudio Melo, Swetlana Hubrig; day astronomer Dominique Naef; Henri Boffin (ESO) processed the data and made the colour-composite, and Haennes Heyer (ESO) made the final adjustments.{{free media}}

"This image is a colour-composite of the barred spiral galaxy NGC 5584. It is based on data collected by the Paranal Science Team with the FORS1 instrument on Kueyen, the second 8.2-m Unit Telescope of ESO's Very Large Telescope. The supernova SN 2007af is the bright object seen slightly below and to the right of the galaxy's centre. The galaxy and its bright supernova were observed on the nights of 16, 19 and 22 March 2007 through a B, V, R, H-alpha and OII filter."[17]

The B filter is centered at 440 nm and the OII filter is centered at 372 nm.[17]

"Located about 75 million light years away towards the constellation Virgo ('the Virgin'), NGC 5584 is a galaxy slightly smaller than the Milky Way. It belongs, however, to the same category: both are barred spirals."[18]

"Spiral galaxies are composed of a 'bulge' and a flat disc. The bulge hosts old stars and usually a central supermassive black hole. Younger stars reside in the disc, forming the characteristic spiral structures from which the galaxies get their name. Barred spirals are crossed by a bright band of stars."[18]

"In this amazing new image of NGC 5584 two dominant spiral arms are clearly visible, while the others are deformed, probably due to interactions with other galaxies. Luminous patches are spread all over the disc, indicating that stars are being formed in this gigantic rose at a frantic pace."[18]

Blues[edit | edit source]

This is a Hubble Space Telescope image of the Crab Nebula showing the diffuse blue region. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University).{{free media}}

"[T]he diffuse blue region is predominantly produced by synchrotron radiation, which is radiation given off by the curving motion of electrons in a magnetic field. The radiation corresponded to electrons moving at speeds up to half the speed of light."[19]

A synchrotron model for the continuum spectrum of the Crab Nebula fits the radiation given off.[20]

Cyans[edit | edit source]

This is an image of the interstellar bubble called Thor's Helmet. Credit: Martin Rusterholz (CXIELO Observatory).{{fairuse}}

The cyanide radical CN- has been identified in interstellar space.[21] The cyanide radical (called cyanogen) is used to measure the temperature of interstellar gas clouds.[22]

"This helmet-shaped cosmic cloud [in the image at right] with wing-like appendages is popularly called Thor's Helmet. Heroically sized even for a Norse god, Thor's Helmet is about 30 light-years across. In fact, the helmet is actually more like an interstellar bubble, blown as a fast wind from the bright, massive star near the bubble's center sweeps through a surrounding molecular cloud. Known as a Wolf-Rayet star, the central star is an extremely hot giant thought to be in a brief, pre-supernova stage of evolution. Cataloged as NGC 2359, the nebula is located about 15,000 light-years away in the constellation Canis Major. The sharp image, made using broadband and narrowband filters, captures striking details of the nebula's filamentary structures. It shows off a blue-green color from strong emission due to oxygen atoms in the glowing gas."[23]

Greens[edit | edit source]

This is an image of NGC 2080, the Ghost Head Nebula. Credit: NASA, ESA and Mohammad Heydari-Malayeri (Observatoire de Paris, France).{{free media}}

At right is a Hubble Space Telescope image of the Ghost Head Nebula. "This nebula is one of a chain of star-forming regions lying south of the 30 Doradus nebula in the Large Magellanic Cloud. The red and blue light comes from regions of hydrogen gas heated by nearby stars. The green light comes from glowing oxygen, illuminated by the energy of a stellar wind. The white center shows a core of hot, massive stars."[24]

Yellows[edit | edit source]

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.[25]

Oranges[edit | edit source]

The robotic Cassini spacecraft orbiting Saturn captured the heavily cratered Tethys slipping behind Saturn's atmosphere-shrouded Titan late last year. Credit: Cassini Imaging Team, ISS, JPL, ESA, NASA.{{free media}}

In the image at the right, "Titan shows not only its thick and opaque orange lower atmosphere, but also an unusual upper layer of blue-tinted haze."[26]

Titan is an orange source in orbit around Saturn.

Saturn takes 29.5 years to orbit the Sun, spending about 2.46 years in each sign of the zodiac.

Reds[edit | edit source]

Milky Way is viewed by H-Alpha Sky Survey. Credit: David Brown and Douglas Finkbeiner.{{fairuse}}

"Spectra of the helium 2.06 µm and hydrogen 2.17 µm lines ... confirm the existence of an extended region of high-velocity redshifted line emission centered near [Sgr A*/IRS 16]."[27]

Infrareds[edit | edit source]

This Hubble image of the Egg Nebula shows one of the best views to date of the brief but dramatic preplanetary, or protoplanetary nebula phase in a star’s life. Credit: ESA/Hubble & NASA.{{free media}}

Infrared astronomy deals with the detection and analysis of infrared radiation (wavelengths longer than red light). Except at wavelengths close to visible light, infrared radiation is heavily absorbed by the atmosphere, and the atmosphere produces significant infrared emission. Consequently, infrared observatories have to be located in high, dry places or in space. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets and circumstellar disks. Longer infrared wavelengths can also penetrate clouds of dust that block visible light, allowing observation of young stars in molecular clouds and the cores of galaxies.[28] Some molecules radiate strongly in the infrared. This can be used to study chemistry in space; more specifically it can detect water in comets.[29]

"The NASA/ESA Hubble Space Telescope has been at the cutting edge of research into what happens to stars like our Sun at the ends of their lives ... One stage that stars pass through as they run out of nuclear fuel is the preplanetary, or protoplanetary nebula. This Hubble image [at right] of the Egg Nebula shows one of the best views to date of this brief but dramatic phase in a star’s life."[30]

"The preplanetary nebula phase is a short period in the cycle of stellar evolution — over a few thousand years, the hot remains of the star in the centre of the nebula heat it up, excite the gas, and make it glow as a planetary nebula. The short lifespan of preplanetary nebulae means there are relatively few of them in existence at any one time. Moreover, they are very dim, requiring powerful telescopes to be seen. This combination of rarity and faintness means they were only discovered comparatively recently. The Egg Nebula, the first to be discovered, was first spotted less than 40 years ago, and many aspects of this class of object remain shrouded in mystery."[30]

"At the centre of this image, and hidden in a thick cloud of dust, is the nebula’s central star. While we can’t see the star directly, four searchlight beams of light coming from it shine out through the nebula. It is thought that ring-shaped holes in the thick cocoon of dust, carved by jets coming from the star, let the beams of light emerge through the otherwise opaque cloud. The precise mechanism by which stellar jets produce these holes is not known for certain, but one possible explanation is that a binary star system, rather than a single star, exists at the centre of the nebula."[30]

"The onion-like layered structure of the more diffuse cloud surrounding the central cocoon is caused by periodic bursts of material being ejected from the dying star. The bursts typically occur every few hundred years."[30]

"The distance to the Egg Nebula is only known very approximately, the best guess placing it at around 3000 light-years from Earth. This in turn means that astronomers do not have any accurate figures for the size of the nebula (it may be larger and further away, or smaller but nearer). This image is produced from exposures in visible and infrared light from Hubble’s Wide Field Camera 3."[30]

Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.

Sun[edit | edit source]

This is a visual image of the outer surface of the photosphere of the Sun with some sunspots (holes in the photosphere). Credit: NASA.

The visible light we see from the outer surface of the photosphere is produced as electrons react with hydrogen atoms to produce H ions.[31][32] This indicates that the outer surface of the Sun's photosphere is a primary source of visual radiation.

Hypotheses[edit | edit source]

  1. Sources of each specific radiation may be hidden from view.

See also[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 Alastair McBeath (October 1991). "Shower Meteor Colors". WGN 19 (5): 198-205. http://articles.adsabs.harvard.edu//full/1991JIMO...19..198M/0000198.000.html. Retrieved 2013-05-31. 
  2. J. R. Webb; M. T. Carini; S. Clements; S. Fajardo; P. P. Gombola; R. J. Leacock; A. C. Sadun; A. G. Smith. "The 1987-1990 optical outburst of the OVV quasar 3C 279". Astronomical Journal 1990 100: 1452–6. doi:10.1086/115609. 
  3. APOD: December 26, 1998 - Gamma Ray Quasar
  4. Apparent superluminal motion
  5. Anil Bhardwaj; Ronald F. Elsner; G. Randall Gladstone; Thomas E. Cravens; Carey M. Lisse; Konrad Dennerl; Graziella Branduardi-Raymont; Bradford J. Wargelin et al. (June 2007). "X-rays from solar system objects". Planetary and Space Science 55 (9): 1135-89. doi:10.1016/j.pss.2006.11.009. http://www.sciencedirect.com/science/article/pii/S0032063306003370. Retrieved 2013-05-23. 
  6. Markus J. Aschwanden (2007). Erdelyi R. ed. "Fundamental Physical Processes in Coronae: Waves, Turbulence, Reconnection, and Particle Acceleration In: Waves & Oscillations in the Solar Atmosphere: Heating and Magneto-Seismology". Proceedings IAU Symposium 3 (S247): 257–68. doi:10.1017/S1743921308014956. 
  7. Supersoft X-Ray Sources. http://library.thinkquest.org/27930/supersoft.htm. 
  8. 8.0 8.1 White NE; Giommi P; Heise J; Angelini L; Fantasia S. "RX J0045.4+4154: A Recurrent Supersoft X-ray Transient in M31". The Astrophysical Journal Letters 445: L125. http://lheawww.gsfc.nasa.gov/users/white/wgacat/apjl.html. 
  9. 9.0 9.1 9.2 9.3 Feng H, Kaaret P (2006). "Spectral state transitions of the ultraluminous X-RAY sources X-1 and X-2 in NGC 1313". Ap J 650 (1): L75. doi:10.1086/508613. 
  10. 10.0 10.1 Jifeng Liu (March 26, 2005). X-Rays Signal Presence Of Elusive Intermediate-Mass Black Hole. Ann Arbor, Michigan, USA: ScienceDaily. http://www.sciencedaily.com/releases/2005/03/050323132144.htm. Retrieved 2012-11-25. 
  11. Patsourakos, S.; Vial, J.-C. (2002). "Intermittent behavior in the transition region and the low corona of the quiet Sun". Astronomy and Astrophysics 385: 1073–1077. doi:10.1051/0004-6361:20020151. 
  12. 12.0 12.1 J. Lean (14 April 1989). "Contribution of Ultraviolet Irradiance Variations to Changes in the Sun's Total Irradiance". Science 244 (4901): 197–200. doi:10.1126/science.244.4901.197. PMID 17835351. http://www.sciencemag.org/cgi/content/abstract/244/4901/197.  (19% of the 1/1366 total decrease is 1.4% decrease in UV)
  13. M. Fligge, S. K. Solanki (2000). "The solar spectral irradiance since 1700". Geophysical Research Letters 27 (14): 2157–2160. doi:10.1029/2000GL000067. Archived from the original on 28 September 2011. http://web.archive.org/web/20110928123706/http://www.mps.mpg.de/dokumente/publikationen/solanki/j111.pdf. Retrieved 12 June 2011. 
  14. 14.0 14.1 Sten Odenwald (December 16, 2008). ISSUE #66: THE CHEMISTRY OF STARS. Greenbelt, Maryland USA: Goddard Space Flight Center. http://sunearthday.gsfc.nasa.gov/2009/TTT/66_chemistry.php. Retrieved 2013-12-20. 
  15. F. Paresce (December 15, 2009). Hubble's Festive View of a Grand Star-Forming Region. HubbleSite. http://hubblesite.org/newscenter/archive/releases/2009/32/. Retrieved 2013-01-10. 
  16. 16.0 16.1 16.2 Harold Zirin (March 1959). "Physical Conditions in Limb Flares and Active Prominences. II. a Remarkable Limb Flare, December 18, 1956". Astrophysical Journal 129 (3): 414-23. doi:10.1086/146633. 
  17. 17.0 17.1 Susana Randall; Claudio Melo; Swetlana Hubrig; Dominique Naef; Henri Boffin; Haennes Heyer (March 27, 2007). The Spiral Galaxy NGC 5584 and SN 2007af. Kueyen: European Southern Observatory. http://www.eso.org/public/images/eso0716a/. Retrieved 2013-03-27. 
  18. 18.0 18.1 18.2 Susana Randall; Claudio Melo; Swetlana Hubrig; Dominique Naef; Henri Boffin; Haennes Heyer (March 27, 2007). The Purple Rose of Virgo. La Silla: European Southern Observatory. http://www.eso.org/public/news/eso0716/. Retrieved 2013-03-27. 
  19. Iosif Shklovskii (1953). "On the Nature of the Crab Nebula’s Optical Emission". Doklady Akademii Nauk SSSR 90: 983. 
  20. B. J. Burn (1973). "A synchrotron model for the continuum spectrum of the Crab Nebula". Monthly Notices of the Royal Astronomical Society 165: 421. 
  21. Piotr A. Pieniazek; Stephen E. Bradforth; Anna I. Krylov (2005-12-07). "Spectroscopy of the Cyano Radical in an Aqueous Environment" (PDF). The Journal of Physical Chemistry. A (Los Angeles, California 90089-0482: Department of Chemistry, University of Southern California) 110 (14): 4854–65. doi:10.1021/jp0545952. PMID 16599455. 
  22. Roth, K. C.; Meyer, D. M.; Hawkins, I. (1993). "Interstellar Cyanogen and the Temperature of the Cosmic Microwave Background Radiation" (pdf). The Astrophysical Journal 413 (2): L67–L71. doi:10.1086/186961. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1993ApJ...413L..67R&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf. 
  23. Robert Nemiroff; Jerry Bonnell (March 7, 2013). Astronomy Picture of the Day -- Thor's Helmet. Greenbelt, Maryland USA: NASA Goddard Space Flight Center. http://www.freerepublic.com/focus/f-chat/2994668/posts. Retrieved 2014-02-22. 
  24. News Release Number: STScI-2001-34 (December 19, 2001). Wallpaper: The Ghost-Head Nebula (NGC 2080). NASA and the Hubble Space Telescope. http://hubblesite.org/gallery/wallpaper/pr2001034a/. Retrieved 2012-07-21. 
  25. Alpha Mic, Jim Kaler, Stars. Accessed on line September 4, 2008.
  26. Robert Nemiroff; Jerry Bonnell (27 January 2010). Tethys Behind Titan. Greenbelt, Maryland USA: NASA Goddard Space Flight Center. http://apod.nasa.gov/apod/ap100127.html. Retrieved 1 March 2014. 
  27. T. R. Geballe; K. Krisciunas; J. A. Bailey; R. Wade (April 1, 1991). "Mapping of infrared helium and hydrogen line profiles in the central few arcseconds of the Galaxy". The Astrophysical Journal 370 (4): L73-6. doi:10.1086/185980. http://adsabs.harvard.edu/abs/1991ApJ...370L..73G. Retrieved 2012-08-03. 
  28. Staff (11 September 2003). "Why infrared astronomy is a hot topic". ESA. Retrieved 11 August 2008.
  29. "Infrared Spectroscopy – An Overview". NASA/IPAC. Retrieved 11 August 2008.
  30. 30.0 30.1 30.2 30.3 30.4 ESA/Hubble; NASA (April 23, 2012). Hubble images searchlight beams from a preplanetary nebula. ESA/Hubble & NASA. http://www.spacetelescope.org/images/potw1217a/. Retrieved 2013-01-10. 
  31. E.G. Gibson (1973). The Quiet Sun. NASA. 
  32. F.H. Shu (1991). The Physics of Astrophysics. 1. University Science Books. ISBN 0-935702-64-4. 

External links[edit | edit source]

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