Astronomical Naming Conventions - Comets

Comets

The names given to comets have followed several different conventions over the past two centuries. Before any systematic naming convention was adopted, comets were named in a variety of ways. The first one to be named was "Halley's Comet" (now officially known as Comet Halley), named after Edmond Halley, who had calculated its orbit. Similarly, the second known periodic comet, Comet Encke (formally designated 2P/Encke), was named after the astronomer, Johann Franz Encke, who had calculated its orbit rather than the original discoverer of the comet, Pierre Méchain. Other comets that bore the possessive include "Biela's Comet" (3D/Biela) and "Miss Herschel's Comet" (35P/Herschel-Rigollet, or Comet Herschel-Rigollet). Most bright (non-periodic) comets were referred to as 'The Great Comet Of...' the year in which they appeared.

In the early 20th century, the convention of naming comets after their discoverers became common, and this remains today. A comet is named after up to its first three independent discoverers. In recent years, many comets have been discovered by instruments operated by large teams of astronomers, and in this case, comets may be named for the instrument (for example, Comet IRAS-Araki-Alcock (C/1983 H1) was discovered independently by the IRAS satellite and amateur astronomers Genichi Araki and George Alcock). Comet 105P/Singer Brewster, discovered by Stephen Singer-Brewster, should by rights have been named "105P/Singer-Brewster", but this would have led most readers to believe it had been a joint discovery by two astronomers named Singer and Brewster, respectively, so the hyphen was replaced by a space. Other comets with spaces in their names, however, reflect their discoverers' name spellings (e.g. 32P/Comas Solá).

Until 1994, the systematic naming of comets (the "Old Style") involved first giving them a provisional designation of the year of their discovery followed by a lower case letter indicating its order of discovery in that year (e.g. the first Comet Bennett is 1969i, the 9th comet discovered in 1969). In 1987, more than 26 comets were discovered, so the alphabet was used again with a "1" subscript, very much like what is still done with asteroids (an example is Comet Skorichenko-George, 1989e1). The record year was 1989, which went as high as 1989h1. Once an orbit had been established, the comet was given a permanent designation in order of time of perihelion passage, consisting of the year followed by a Roman numeral. For example, Comet Bennett (1969i) became 1970 II.

Increasing numbers of comet discoveries made this procedure difficult to operate, and in 2003 the IAU's Committee on Small Body Nomenclature approved a new naming system, and in 2004 the IAU approved a new designation system The Comets are now designated by the year of their discovery followed by a letter indicating the half-month of the discovery (A denotes the first half of January, B denotes the second Half of January, C denotes the first half of February, D denotes the second half of February, etcetera) and a number indicating the order of discovery. To exemplify, the fourth comet discovered in the second half of February 2006 would be designated 2006 D4. "I" and "Z" are not used when describing the half of a particular month the comet was discovered. Prefixes are also added to indicate the nature of the comet, with P/ indicating a periodic comet, C/ indicating a non-periodic comet, X/ indicating a comet for which no reliable orbit could be calculated (typically comets described in historical chronicles), D/ indicating a comet which has broken up or been lost, and A/ indicating an object at first thought to be a comet but later reclassified as an asteroid. Periodic comets also have a number indicating the order of their discovery. Thus Bennett's comet has the systematic designation C/1969 Y1. Halley's Comet, the first comet to be identified as periodic, has the systematic name 1P/1682 Q1. Comet Hale-Bopp's systematic name is C/1995 O1. The famous Comet Shoemaker-Levy 9 was the ninth periodic comet jointly discovered by Carolyn Shoemaker, Eugene Shoemaker, and David Levy (the Shoemaker-Levy team has also discovered four non-periodic comets interspersed with the periodic ones), but its systematic name is D/1993 F2 (it was discovered in 1993 and the prefix "D/" is applied, since it was observed to crash into Jupiter).

Some comets were first spotted as minor planets, and received a temporary designation accordingly before cometary activity was later discovered. This is the reason for such comets as P/1999 XN₁₂₀ (Catalina 2) or P/2004 DO₂₉ (Spacewatch-LINEAR). The MPECs and html version of IAUCs, because of their telegraphic style, "flatten out" the subscripts, but PDF version of IAUCs and some other sources such as the Yamamoto Circulars and the Kometnyj Tsirkular use them.

See also: Astronomical objects named after people