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The image shows Comet McNaught. Credit: fir0002.

A comet is a small solar system body that has a solid icy nucleus. When near the Sun a comet can also have an extremely tenuous atmosphere called the coma which can grow into a large and bright tail.


An image of Christensen who discovered C/2006 W3 (Christensen). Credit: .


Comet Lovejoy survives it sun-grazing cruise around the Sun and back into space (Dec. 15-16, 2011). Credit:{{free media}}

Still other comets have dangerously close orbits to the Sun and dozens have been found in recent years plummeting into our nearest star by solar observing spacecraft.

"Sun-grazing comets almost never re-emerge, but their sublimative destruction near the sun has only recently been observed directly, while chromospheric impacts have not yet been seen, nor impact theory developed."[1] "[N]uclei are ... destroyed by ablation or explosion ... in the chromosphere, producing flare-like events with cometary abundance spectra."[1]

"The death of a comet at r ~ R has been seen directly only very recently (Schrijver et al 2011) using the SDO AIA XUV instrument. This recorded sublimative destruction of Comet C/2011 N3 as it crossed the solar disk very near periheloin q = 1.139Rʘ."[1]

"The phenomenon of flare induced sunquakes - waves in the photosphere - discovered by Kosovichev and Zharkova (1998) and now widely studied (e.g. Kosovichev 2006) should also result from the momentum impulse delivered by a cometary impact."[1]

Comet Bennett 1970 II[edit]

The velocities of the cyan molecule as produced in the head of comet Bennett 1970 II have been measured.[2]

Comet Borrelly[edit]

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

"A typical comet nucleus has an albedo of 0.04.[3]"[4]

"This image, taken by Deep Space 1 on September 22, 2001, has been enhanced to reveal dust being ejected from the nucleus of comet Borrelly. As a result, the nucleus, which is about eight kilometers (about five miles) long, is bright white in the image. The main dust jet is directed towards the bottom left of the frame, around 35 degrees away from the comet-Sun line. The jet emerges as actually comprised of at least three smaller features. This active region as a whole is at least three kilometers (less than two miles) long."[5]

"Another, smaller, jet feature is seen on the tip of the nucleus on the lower right-hand limb. Dust also seems to be ejected from there into the night-side hemisphere, probably from the dayside hemisphere. The expansion of the gas and dust mixture into the vacuum of space has swept some material around the body of the nucleus so that it appears above the night-side hemisphere. The night-side of the nucleus could not be seen, of course."[5]

"The line between day and night on the comet is towards the upper right. This representation shows a faint ring of brightness separated from the terminator by a dark, unlit area. It is possible that this is a crater rim, seen in grazing illumination, which is just about to cross into darkness as the comet rotates. The direction to the Sun is directly downwards."[5]

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

"Comets are sometimes described as "dirty snowballs," but a close flyby of one by NASA's Deep Space 1 spacecraft last fall detected no frozen water on its surface."[6]

"The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice."[7]

"We know the ice is there. It's just well-hidden. Either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice."[7]

"The Deep Space 1 science team released pictures and other initial findings days after the spacecraft flew within 2,171 kilometers (1,349 miles) of the comet's solid nucleus on September 22, 2001."[6]

"Comet Borrelly is in the inner solar system right now, and it's hot, between 26 and 71 degrees Celsius (80 and 161 degrees Fahrenheit), so any water ice on the surface would change quickly to a gas. As the components evaporate, they leave behind a crust, like the crust left behind by dirty snow."[8]

"It seems to be covered in this dark material, which has been loosely connected with biological material. This suggests that comets might be a transport mechanism for bringing the building blocks of life to Earth."[8]

"It's remarkable how much information Deep Space 1 was able to gather at the comet, particularly given that this was a bonus assignment for the probe."[9]

Comet C/2013 A1 Siding Spring[edit]

"A comet that flew close to Mars showered the red planet with fine cometary dust, according to observations by a trio of spacecraft."[10]

"Comet C/2013 A1 Siding Spring passed within 139,500 kilometres of the red planet on 19 October, the closest a comet has ever been seen to come to a planet without actually colliding with it. To avoid being damaged by the comet dust, all spacecraft orbiting Mars moved to the far side of the planet for 20 minutes while the comet dust was at its most intense, but this did not prevent them from studying the effects it had on Mars’ atmosphere."[10]

“They call this comet encounter a once-in-a-lifetime event, but it’s more like once in a million years.”[11]

"The European Space Agency’s Mars Express spacecraft detected an increase in electrons in Mars’ upper atmosphere, partly ionising it. This was attributed to fine cometary dust penetrating the atmosphere, which led to a meteor storm of thousands of meteors per hour. The increase in electrons led to the creation of a temporary new layer of charged particles in the ionosphere, which runs from an altitude of 120 kilometres to several hundred kilometres above. This is the first time such an event has been seen, even on Earth the extra density of electrons was measured to be five to ten times higher than normal by NASA’s Mars Reconnaissance Orbiter. Another NASA spacecraft, MAVEN, which also observed the new layer in the ionosphere, will monitor for any long-term events as it goes about its regular duties of studying Mars’ atmosphere."[10]

"MAVEN’s Imaging Ultraviolet Spectrograph was able to ascertain the species of ions that flooded into the ionosphere from the comet, the first time a comet that has come direct from the distant Oort Cloud has been sampled in this way. It detected the signal of magnesium, iron and sodium ions following the meteor shower, a signal that dominated Mars’ ultraviolet spectrum for hours afterwards, taking two days to dissipate."[10]

"The results show that dust from the comet, which has a nucleus two kilometres across, according to high resolution images from the Mars Reconnaissance Orbiter, had a dramatic effect on Mars’ atmosphere."[10]

“Observing the effects on Mars of the comet’s dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harm’s way.”[12]

Comet 67P/Churyumov-Gerasimenko[edit]

This is an image of the nucleus of Comet 67P/Churyumov-Gerasimenko by Rosetta. Credit: ESA Rosetta Mission.

Comet Halley[edit]

“During the Halley Monitoring Program at La Silla from Feb.17 to Apr.17,1986 ... In the light of the neutral CN-radical a continuous formation and expansion of [cyan] gas-shells could be observed.”[13] “The gas-expansion velocity decreases with increasing heliocentric distance from 1 km/s in early March to 0.8 km/s in April.”[13]


The image shows Comet 17P/Holmes. Credit: .
Comet Holmes (17P/Holmes) in 2007 shows a blue ion tail on the right. Credit: Ivan Eder.
These images are of comet Holmes. The contrast has been enhanced for the right image to show anatomy. Credit: NASA/JPL-Caltech/W. Reach (SSC-Caltech).

On Oct 23, 2007, J. A. Henríquez Santana in the Canary Islands and Ramón Naves in Barcelona noticed an impressive spectacle, a bright and large comet gleemed through the bright full moon in the constellation Perseus. This was not a new comet, yet it was a supposedly boring one. The comet 17P Holmes was supposed to be a meagre 17th magnitude, far too dim for most telescopes to even detect in the bright moonlight.

The comet had suddenly brightened a half a million times and was easily seen by the unaided eye. Such is the importance of keeping an eye out for changes in a known comets. Within days, the most powerful telescopes on the Earth (and the one above it, the Hubble Space Telescope) would be viewing it.

So I make it a daily ritual to check out and record as many details as I can about each viewable comet and like to be aware for new things while I'm at my telescope.

An extremely good web page for comets is Greg Crinklaw's Skyhound and by coincidence Holmes is coming out of the glare fo the sun. We should keep tabs on it!

In the second image pair, "NASA's Spitzer Space Telescope captured the picture on the left of comet Holmes in March 2008, five months after the comet suddenly erupted and brightened a millionfold overnight. The contrast of the picture has been enhanced on the right to show the anatomy of the comet."[14]

"Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes mysteriously exploded as it approached the asteroid belt. Astronomers still do not know the cause of these eruptions."[14]

"Spitzer's infrared picture at left reveals fine dust particles that make up the outer shell, or coma, of the comet. The nucleus of the comet is within the bright whitish spot in the center, while the yellow area shows solid particles that were blown from the comet in the explosion. The comet is headed away from the sun, which lies beyond the right-hand side of the picture."[14]

"The contrast-enhanced picture on the right shows the comet's outer shell, and strange filaments, or streamers, of dust. The streamers and shell are a yet another mystery surrounding comet Holmes. Scientists had initially suspected that the streamers were small dust particles ejected from fragments of the nucleus, or from hyperactive jets on the nucleus, during the October 2007 explosion. If so, both the streamers and the shell should have shifted their orientation as the comet followed its orbit around the sun. Radiation pressure from the sun should have swept the material back and away from it. But pictures of comet Holmes taken by Spitzer over time show the streamers and shell in the same configuration, and not pointing away from the sun. The observations have left astronomers stumped."[14]

"The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the comet in its orbit."[14]

"The Spitzer picture was taken with the spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns."[14]

Comet Kohoutek 1973 XII[edit]

The neutral cyan coma of comet Kohoutek 1973 XII is measured.[15]

Comet Lovejoy[edit]

Comet Lovejoy has a blue ion tail leading away off to the left. Credit: NASA/Dan Burbank.
Comet Lovejoy is detected in STEREO/SECCHI's EUVI-A imager's 17.1-nm wavelength. Credit: STEREO/SECCHI image courtesy NASA/NRL.

At right is Comet Lovejoy as detected in STEREO/SECCHI's EUVI-A imager's 17.1-nm wavelength. "The comet is clearly visible racing away from the Sun, leaving a wiggly-tail in its wake! Why the wiggles? We're not sure -- we need to start studying that when we get all of the spacecraft data from STEREO-B this weekend. However, we think there may some kind of helical motion going on, or perhaps there's a projection affect and we're seeing tail material magnetically "clinging" to coronal loops and moving with them. There are other possibilities too, though, and we will certainly investigate those! We should have equivalent images from the STEREO-A spacecraft which we will also get this weekend. When we pair these together, and throw in the SDO images too, we should be able to get an incredibly unique 3-D picture of how this comet is reacting the the intense coronal heat and magnetic loops."[16]

Comet Lulin[edit]

Recent changes in Comet Lulin's greenish coma and tails are shown in these two panels taken on January 31st (top) and February 4th (bottom) 2009. In both views the comet has an apparent antitail to the left of the coma of dust. Credit: Joseph Brimacombe, Cairns, Australia.

Shown at the right "Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight".[17]

Comet McNaught[edit]

McNaught Comet is captured in visual color with a Canon 350D...EF50...F2...25 sec. Credit: Davewhite7.

Comet PanSTARRS C/2012 K1[edit]

Sweeping slowly through northern skies, the comet PanSTARRS C/2012 K1 posed for this telescopic portrait on June 2nd in the constellation Ursa Major. Credit: Alessandro Falesiedi.

On the right is a visual image of comet PanSTARRS C/2012 K1.

"Now within the inner solar system, the icy body from the Oort cloud sports two tails, a lighter broad dust tail and crooked ion tail extending below and right. The comet's condensed greenish coma makes a nice contrast with the spiky yellowish background star above. NGC 3319 appears at the upper left of the frame that spans almost twice the apparent diameter of the full Moon."[18]

Comet Schwassmann-Wachmann I (P/SW-1)[edit]

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

"NASA's new Spitzer Space Telescope has captured [the image right] of an unusual comet that experiences frequent outbursts, which produce abrupt changes in brightness. Periodic comet Schwassmann-Wachmann I (P/SW-1) has a nearly circular orbit just outside that of Jupiter, with an orbital period of 14.9 years. It is thought that the outbursts arise from the build-up of internal gas pressure as the heat of the Sun slowly evaporates frozen carbon dioxide and carbon monoxide beneath the blackened crust of the comet nucleus. When the internal pressure exceeds the strength of the overlying crust, a rupture occurs, and a burst of gas and dust fragments is ejected into space at speeds of 450 miles per hour (200 meters per second)."[19]

"This 24-micron image of P/SW-1 was obtained with Spitzer's multiband imaging photometer. The image shows thermal infrared emission from the dusty coma and tail of the comet. The nucleus of the comet is about 18 miles (30 kilometers) in diameter and is too small to be resolved by Spitzer. The micron-sized dust grains in the coma and tail stream out away from the Sun. The dust and gas comprising the comet's nucleus is part of the same primordial materials from which the Sun and planets were formed billions of years ago. The complex carbon-rich molecules they contain may have provided some of the raw materials from which life originated on Earth."[19]

"Schwassmann-Wachmann 1 is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the solar system."[19]

Comet Swan[edit]

This is a real color composite image of Comet Swan. Credit: Ginger Mayfield.

"Comet Swan recently made a swing through the inner solar and emerged in the evening sky. Astronomy enthusiast Ginger Mayfield recorded the blue-green color of the comet's nucleus and a tenuous tail in this composite created from multiple images taken on October 26 from Divide, Colorado."[20]

Comet West 1976 VI[edit]

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.

The physical parameters of the neutral cyan coma of comet West (1975n) have been measured.[21]

Kuiper Belt[edit]

Occasionally inteferences with the large gas giants of our solar system (Jupiter and Saturn) will further alter their orbit. These comets commonly roam in an area called the Kuiper belt, that surrounds the last planet Neptune. The orbits of these comets vary highly from the diminuitive comet Encke (3 years) to the famed comet Halley seen only once maybe twice a lifetime (76 years).

Oort Cloud[edit]

Most of the comets lay at the distant reaches of our system in a hypothesized Oort cloud. At the very edge of the solar these comets orbit in very large loops around the distant reaches of our solar system. The passing of nearby stars, or other objects can alter their orbit, sending them speeding towards the inner reaches of our solar system. these comets typically retain very large orbits such that they will not return (once seen in the inner solar system) for many thousands of years.

Solar binary[edit]

Main sources: Stars/Sun/Binary and Solar binary

The Sun-Jupiter binary may serve to establish an upper limit for interstellar cometary capture when three bodies are extremely unequal in mass, such as the Sun, Jupiter, and a third body (potential comet) at a large distance from the binary.[22] The basic problem with a capture scenario even from passage through “a cloud of some 10 million years, or from a medium enveloping the solar system, is the low relative velocity [~0.5 km s-1] required between the solar system and the cometary medium.”[23] The capture of interstellar comets by Saturn, Uranus, and Neptune together cause about as many captures as Jupiter alone.[23]

Comet-seeker telescopes[edit]

"A comet seeker is a type of small telescope adapted especially to searching for comets: commonly of short focal length and large aperture, in order to secure the greatest brilliancy of light."[24]


Irregardless of where comets come from or go. Comets are a regular visitor the inner solar system. Because comets cannot be detected at the furthest reaches of our solar system, there is always the chance for a dramatic visit by a truly well-traveled visitor. Amatuer astronomers have been enthusiastic searchers for these cosmic visitor since the beginning of time and according to astronomical convention, whomever first finds the comets, has their name immortalized in the heavens.

Currently visible in a small scope (6" or less)[edit]

Comets visible during October 2008 (place any observations below and include time, date, location, and any observable features)

17P/Holmes: A morning comet near Cancer visible in binoculars

Very good to see as it has not been widely seen yet, its brightness and location might be useful to report

C/2008 A1 (McNaught): An evening comet in Ophiuchus visible in binoculars

C/2006 W3 (Christensen): A evening comet in Cassiopeia visible in small telescopes

* Tough comet in a smalltown sky (5.0magn); I see a spherical 3' glow with little condensation and no nucleus.--Jolie (254mm reflector at 79X at Fri Oct 24,08 2:45UTC)
* Hazy conditions, and much light pollution. --mikeu (16" f/10 SCT with CCD on 2008-11-22T02:53:23 UTC)

C/2006 OF2 (Broughton): A morning comet in Camelopardalis visible in small telescopes

* Dim but definite in a smalltown sky (5.0magn); spherical with some condensation and a very faint nucleus. --Jolie (254mm reflector at 79X at Fri Oct 24,08 5:55UTC)

19P/Schwassmann-Wachmann: A morning comet in Cancer visible in small telescopes

good to keep a watch on as it had a tendency for outbursts

C/2008 J1 (Boattini): A far-northern evening comet in Camelopardalis visible in a 6-inch telescope

205P/Giacobini: An evening comet in Aquarius visible in a 6-inch telescope

Exploratory astronomy[edit]

"Deep Space 1 was launched in October 1998 as part of NASA's New Millennium Program, which is managed by JPL for NASA's Office of Space Science, Washington, D.C. The California Institute of Technology manages JPL for NASA."[5]

"Deep Space 1 completed its primary mission testing ion propulsion and 11 other advanced, high-risk technologies in September 1999. NASA extended the mission, taking advantage of the ion propulsion and other systems to undertake this chancy but exciting, and ultimately successful, encounter with the comet."[5]

See also[edit]


  1. 1.0 1.1 1.2 1.3 J.C. Brown, H.E. Potts, L.J. Porter, & G.le Chat (November 8, 2011). "Mass Loss, Destruction and Detection of Sun-grazing & -impacting Cometary Nuclei". Astronomy & Astrophysics 535: 12. doi:10.1051/0004-6361/201015660. Retrieved 2012-11-25. 
  2. I. N. Matveev (1982). "Determination of velocities of cyan molecule production in the head of comet Bennett 1970 II". Kometnyj Tsirkulyar (286). 
  3. Robert Roy Britt (2001-11-29). "Comet Borrelly Puzzle: Darkest Object in the Solar System". Archived from the original on 22 January 2009. Retrieved 2012-09-01. 
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  12. Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  13. 13.0 13.1 Wolfhard Schlosser, Rita Schulz, Paul Koczet (1986). The cyan shells of Comet P/Halley, In: Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. 3. European Space Agency. pp. 495-8. Bibcode: 1986ESASP.250c.495S. 
  14. 14.0 14.1 14.2 14.3 14.4 14.5 Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  15. RS Amirkhanov, KI Churyumov, Gorodetsij (1978). "Physical parameters of the neutral cyan coma of comet Kohoutek, 1973 XII.". Kometnyj Tsirkulyar (220). 
  16. Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  17. James A. Phillips (2009). "Green Comet Approaches Earth". National Aeronautics and Space Administration Science News. Retrieved 2012-05-05. 
  18. Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  19. 19.0 19.1 19.2 Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  20. Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).
  21. V. A. Oshchepkov, N. M. Shiper (1978). "Physical parameters of the neutral cyan coma of comet West (1975n)". Kometnyj Tsirkulyar (234). 
  22. MJ Valtonen (February 1983). "On the capture of comets into the Solar System". The Observatory 103 (2): 1-4. 
  23. 23.0 23.1 M. J. Valtonen; K. A. Innanen (April 1982). "The capture of interstellar comets". The Astrophysical Journal 255 (4): 307-15. doi:10.1086/159830. 
  24. Lua error in Module:Citation/CS1 at line 3505: bad argument #1 to 'pairs' (table expected, got nil).

External links[edit]

{{astronomy resources}}