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Astronomical naming conventions
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== Comets == {{Further|Naming of comets|Provisional designation in astronomy#Comets}} The names given to [[comet]]s 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 its first independent discoverers, up to a maximum of three names, separated by hyphens.<ref name="guideline" /><ref name="Gibilisco1985">{{cite book|author=Stan Gibilisco|author-link=Stan Gibilisco|title=Comets, meteors & asteroids--how they affect Earth|url=https://archive.org/details/cometsmeteorsast00gibi|url-access=registration|access-date=19 December 2012|date=1 August 1985|publisher=Tab Books|isbn=978-0-8306-1905-4|page=[https://archive.org/details/cometsmeteorsast00gibi/page/76 76]|quote=What if two or more different people discover the same comet at about the same time? This problem is solved by allowing a comet to bear as many as three names. The names are separated by hyphens. Thus we have had comets such as Ikeya-Seki and Arend-Roland. It has been decided that more than three names would be ridiculous and cumbersome. Therefore, we do not hear of comets such as Jones-Smith-James-Olson-Walters-Peterson-Garcia-Welch!}}</ref> The IAU prefers to credit at most two discoverers, and it credits more than three discoverers only when "in rare cases where named lost comets are identified with a rediscovery that has already received a new name."<ref name="guideline" /> 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 could be misinterpreted as a joint discovery by two astronomers named Singer and Brewster, respectively, so the hyphen was replaced by a space.<ref name="machholz">{{citation |journal= Journal of the Association of Lunar and Planetary Observers |title= Comet corner |author= Don E. Machholz |author-link= Donald Machholz |volume= 33 |pages= 25–28, 26 |issue= 1|publisher= Association of Lunar and Planetary Observers (U.S.) |year= 1989 |quote= A hyphen (-) is used in a comet's name only to separate the discoverers. Thus, when sometimes the discover has a double name, the hyphen is dropped from the comet's name in order to show that there was only one discoverer. For example, in 1986 Stephen Singer-Brewster discovered a comet. It is known as "Comet Singer Brewster." |bibcode = 1989JALPO..33...25M }} Go to [http://adsabs.harvard.edu/journals_service.html the journal search in the Astrophysics Data System], pick "Journal of the Association of Lunar and Planetary Observers", volume "33", page "26". It's not in the list of abstracts, you have to check the page thumbnails.</ref> The spaces, apostrophes and other characters in discoverer names are preserved in comet names, like [[32P/Comas Solà]], [[6P/d'Arrest]], [[53P/Van Biesbroeck]], [[Comet van den Bergh (1974g)]], [[66P/du Toit]],<ref name="machholz" /> or [[57P/du Toit–Neujmin–Delporte]]. 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,<ref name="guideline">[http://www.cbat.eps.harvard.edu/cometnameg.html IAU Comet-naming Guidelines] {{webarchive |url=https://web.archive.org/web/20160304050435/http://www.cbat.eps.harvard.edu/cometnameg.html |date=March 4, 2016 }}, Committee on Small Body Nomenclature of Division III of the IAU</ref> and in its 1994 General Assembly the IAU approved a new designation system that entered into force in 1995 January 1.<ref>[http://www.minorplanetcenter.net/iau/lists/CometResolution.html Cometary Designation System], IAU, First appearing in ''Minor Planet Circulars 23803-4'', then in ''International Comet Quarterly'', '''16''', 127</ref> 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, and so on) 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 that has broken up or been lost, and A/ indicating an object at first thought to be a comet but later reclassified as an asteroid (C/2017 U1 became A/2017 U1, then finally [[1I/ʻOumuamua]]). Objects on hyperbolic orbits that do not show cometary activity also receive an A/ designation (example: A/2018 C2, which became [[C/2018 C2 (Lemmon)]] when cometary activity was detected).<ref name="MPC-A">{{cite web|url=https://minorplanetcenter.net/mpec/K18/K18H54.html|title=MPEC 2018-H54 : 2. A/ Objects|publisher=Minor Planet Center|date=20 April 2018|access-date=12 August 2018}}</ref> 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 (astronomer)|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, because 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 {{mpl|P/1999 XN|120}} ([[Catalina Sky Survey|Catalina]] 2) or {{mpl|P/2004 DO|29}} ([[Spacewatch]]–[[Lincoln Near-Earth Asteroid Research|LINEAR]]). The MPECs and HTML version of IAUCs, because of their telegraphic style, "flatten out" the subscripts, but the PDF version of IAUCs<ref>Compare the [http://www.cbat.eps.harvard.edu/iauc/08700/08797.html HTML] and [http://www.cbat.eps.harvard.edu/iauc/08700/08797.pdf PDF] versions of IAUC 8797: in the PDF version the designation P/{{mp|1999 DN|3}} is written with a subscript.</ref> and some other sources such as the Yamamoto Circulars<!-- YamC --> and the Kometnyj Tsirkular<!-- Komet. Tsirk. --> use them.
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