Observation Comets and Comet Hunting

Cometary amateur astronomers mainly sort between those who observe comets, and those who discover them :-) for more about comets like objects of the solar system, see "Comets" in the Theory section

Observing

Comet Hunting

Observing

Most of observers are interested in looking at comets, passage of which is announced by the specialized sites and media. The pleasure may be prolonged further, when one gets interested in fainter comets

Bright Comets

Fainter Comets

Bright Comets

Brilliant comets usually are occurring every five to 10 years as about each year is bringing a 3-4th magnitude comet in our skies. Most of such apparitions or discoveries are announced by the main amateur astronomy media. Should you look at Spaceweather.Com, Sky & Telescope/SkyTonight.com, or this site, you will be warned of such an event. Charts, magnitude, and various data will help you into the observation. A main hindrance for such comets are suburban skies. Hence you will most usually need binoculars or small instruments to spot and observe such comets. Deep countryside skies, on the other hand, will allow such objects to the naked-eye. A comet is a tiny, 6-mi (10-km) wide, icy body surrounded by a large, Jupiter-wide, whispy atmosphere. The asteroid-like body is called the "comet's nucleus", or "nucleus", as the atmosphere is called the "coma". When such an object comes close to the Sun, the sunlight vaporizes the ice of the nucleus, as jets of dust and gas are spewn in the space, feeding the coma and providing raw material for the tail. The tail is this other typical feature of a comet. Electrically charged atoms and molecules are pushed away from the comet's orbital path, at the right opposite from the Sun. Technically, this is called a "ion tail". It may comes in a variety of sizes and shapes. Some more heavy dust, for example, may be pushed less far away, or the gradation of dust of different weights may yield a fan-shaped tail. On the other hand, the heaviest dust may even linger behind the nucleus, along the orbit path. Technically, this is called a "dust tail", or "anti-tail". When such a feature is extent, it may combine to the ion tail in a variety of ways. Observing a comet is interesting, ranging from its position and motion, to the details of the comet's features, like the head or the tail(s). Photography is interesting and rewarding too. Far greater comets, those obviously seen naked-eye, like the 1996 comet Hyakutake, are finer shows still as comet's tail is extending upon a large portion of the sky. As far as the famed Halley's Comet is concerned, it is viewable from Earth approximately every 76 years. Also known as 1P/Halley, this comet was last viewable from Earth in 1986 and won't be visible again until the middle of 2061

Fainter Comets

Such easy comets always eventually come to an end, that is they fade and head back to the far reaches of the solar system. A way to go further is yourself to head to dedicated sites, like NASA's Comet Observation Home Page (note: this link is not available anymore). Such sites are really interesting as they will provide you with observational data about fainter objects, and as they are the place where afficionados are participating actively to comets' observation. This is a fine way to make comets one of your observation fields. Note that for both bright and faint comets, "P/" hints at periodic comets (usually short-period comets, orbiting in less than 200 years, grossly in the ecliptic plane; most such comets are thought to come from the famous Kuiper Belt; P/ applies too to a comet which has been reported at 2 perihelions) as "C/" refers to a non-periodic comet (usually long-period comets, orbiting in huge periods of time (up to 30 million years), with more diverse inclinations to the ecliptic; most such comets are thought to come from the Oort Cloud; C/ refers too to comets with a hyperbolic or parabolic orbit, hence passing only once in the inner solar system)

Comet Hunting

Comet hunting is the next step. Comet hunting still exist despite that an unvolontarily effect of the automated sky surveys like LINEAR or NEAT tends to spot comets, squeezing the efforts of the amateurs somehow. Such programs were elaborated to search for NEOs, but they readily spot numerous comets. Numerous comet hunters continue to report new findings however. And still more in the southern hemisphere where the LINEAR program has not been implemented yet. The chase is easy indeed. The main rules are an appropriate telescope. The brightest, the widest the field of view, the better. Binoculars may be used too. A good atlas or a planetarium software are useful too, as is a relatively good knowledge of the sky -to know what you are seing and to check that the fuzzy objects you spot are comets, and not galaxies or nebulae. A dark sky and no Moon. Comet hunters are browsing the western and eastern sky some hours after dusk or before dawn, at low power. About 35 x is enough allowing for example findings of the 11th magnitude. A statistic survey shows that more comets have been found in the morning sky. If you spot an object which has no match on the chart, this surely is a comet. The next step is to check whether it's a known comet, as you may have found an already discovered comet. Such sites like those dedicated to comets, or giving the ephemerides for a great number of those are useful. When the discovery is ascertained, it has to be reported to the International Astronomical Union (IAU)'s CBAT site. The CBAT may issue a request for confirming observations which will lead to the definite assertion of the discovery. Comets are usually named from their discoverer. A good site about comet hunting is the Astronomical Society of South Australia Comet Seeking & Meteor Showers Group as "The Discovery of Comet Machholz (Comet 2004 Q2)", by the discoverer himself, is a fine page to read. see a page about how the IAU is naming newly discovered comets and asteroids

As far as comet hunting through the SOHO coronograph pictures is concerned, you may see at Sebastian's Comet Hunt. The comets discovered by SOHO have reached the 3,000 mark by September 2015 as they were discovered on the images taken by the craft's LASCO coronographs. That work is mostly allowed to by the -recently increasing- amateur astronomers who pore over the images provided, like 70 people representing 18 countries. The SOHO comet-sighting website is overwatched by the Naval Research Lab in Washington, D.C. as each confirmed finding is sent to the Minor Planet Center in Cambridge, Mass. Images for comet-sighting have been improved. The comets discovered by SOHO are mostly of the Kreutz sungrazers class by 85 percent, that is comets which are coming very close to the Sun, within 500,000 mi (800,000 km) of the Sun's surface. Such comets just vaporize as they plunge into the solar atmosphere helping astronomers to a better knowledge of comets due to the lot of material vaporized! SOHO is aided by the fact that the Sun's bright light is blocked out by a coronograph, or a built-in occulting disk. On average a new member of the Kreutz family is discovered every three days, with some of the larger members being observed for some 48 hours or more before disappearing behind the occulting disk, scorching to death to the Sun. Other comets discovered by SOHO are belonging to groups of comets which have similar orbits, the Meyer, Marsden, and Kracht groups. Such groups of comets are related between themselves and with day- and nightime meteor showers, coming down -from very far ago or laterly- from parent comets which broke apart. Two groups of sungrazers discovered by crowd science through SOHO data has like a parent Comet 96P and are related to a number of Earth-crossing meteor streams. The Kreutz sungrazers, as far as they are concerned, due to their high number, likely broke from a gigantic comet, about 60 mi (100 km) across, about 1200 A.D -probably the Great Come tof 1106. The Kreutz comets, further, are themselves breaking into pieces all along their orbit, bringing very small chunks, or debris, to hit the Sun! see tentative diagram of family trees. Kreutz sungrazers -from German astronomer Heinrich Kreutz who first studied them- are typically small, about 10 yards wide) and numerous. The solar observatory Solar and Heliospheric Observatory (SOHO) sees one falling into the Sun every few days. Some comets discovered through SOHO are very short period comets, with for example, orbital periods of about 4 years, as they might mostly be 'extinct' comets, having expelled most of their ices since previous, numerous passages, as they would have only little to form a tail or replenish their coma. A unexplained systematic increase in the number of comets around the Sun, on the other hand has been recently observed. Some comets passing at the Sun are non-group comets, meaning they are not part of any known family of comets. The next solar observatory, NASA's twin STEREO, launching in February 2006, is likely to allow further discoveries, both through a coronograph and an heliospheric imager, as SOHO might continue to be used for comet hunting only some more decades