Naming of comets

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Comet McNaught, named after its discoverer Robert H. McNaught. It is also known as the Great Comet of 2007 and has the numerical designation C/2006 P1. Comet P1 McNaught02 - 23-01-07.jpg
Comet McNaught, named after its discoverer Robert H. McNaught. It is also known as the Great Comet of 2007 and has the numerical designation C/2006 P1.

Comets have been observed for over 2,000 years. During that time, several different systems have been used to assign names to each comet, and as a result many comets have more than one name.


The simplest system names comets after the year in which they were observed (e.g. the Great Comet of 1680). Later a convention arose of using the names of people associated with the discovery (e.g. Comet Hale–Bopp) or the first detailed study (e.g. Halley's Comet) of each comet. During the twentieth century, improvements in technology and dedicated searches led to a massive increase in the number of comet discoveries, which led to the creation of a numeric designation scheme. The original scheme assigned codes in the order that comets passed perihelion (e.g. Comet 1970 II). This scheme operated until 1994, when continued increases in the numbers of comets found each year resulted in the creation of a new scheme. This system, which is still in operation, assigns a code based on the type of orbit and the date of discovery (e.g. C/2012 S1).

Named by year

The Great January Comet of 1910, named after the date it appeared Comet 1910 A1.jpg
The Great January Comet of 1910, named after the date it appeared

Before any systematic naming convention was adopted, comets were named in a variety of ways. Prior to the early 20th century, most comets were simply referred to by the year when they appeared e.g. the "Comet of 1702".

Particularly bright comets which came to public attention (i.e. beyond the astronomy community) would be described as the great comet of that year, such as the "Great Comet of 1680" and "Great Comet of 1882". If more than one great comet appeared in a single year, the month would be used for disambiguation e.g. the "Great January comet of 1910". Occasionally other additional adjectives might be used.

Named after people

Possibly the earliest comet to be named after a person was Caesar's Comet in 44 BC, which was so named because it was observed shortly after the assassination of Julius Caesar and was interpreted as a sign of his deification. Later eponymous comets were named after the astronomer(s) who conducted detailed investigations on them, or later those who discovered the comet.


Halley's Comet, named after Edmond Halley who first calculated its orbit. It now has the numerical designations 1P/Halley and 1P/1682 Q1. Halley's Comet, 1910.JPG
Halley's Comet, named after Edmond Halley who first calculated its orbit. It now has the numerical designations 1P/Halley and 1P/1682 Q1.

After Edmond Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759, that comet became known as Halley's Comet. [1] Similarly, the second and third known periodic comets, Encke's Comet [2] and Biela's Comet, [3] were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their apparition.


Comet Holmes, named after its discoverer Edwin Holmes. It also has the numerical designation 17P/Holmes. 17pHolmes 071104 eder vga.jpg
Comet Holmes, named after its discoverer Edwin Holmes. It also has the numerical designation 17P/Holmes.

The first comet to be named after the person who discovered it, rather than the one who calculated its orbit, was Comet Faye  – discovered by Hervé Faye in 1843. However, this convention did not become widespread until the early 20th century. It remains common today.

A comet can be named after up to three discoverers, either working together as a team or making independent discoveries (without knowledge of the other investigator's work). The names are hyphenated together, using en dashes where possible. For example, Comet Swift–Tuttle was found first by Lewis Swift and then by Horace Parnell Tuttle a few days later; the discoveries were made independently and so both are honoured in the name. When the discoverer has a hyphenated surname (e.g. Stephen Singer-Brewster), the hyphen is replaced by a space (105P/Singer Brewster) to avoid confusion.

From the late 20th century onwards, many comets have been discovered by large teams of astronomers, so may be named for the collaboration or instrument they used. For example, 160P/LINEAR was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) team. Comet IRAS–Araki–Alcock was discovered independently by a team using the Infrared Astronomy Satellite (IRAS) and the amateur astronomers Genichi Araki and George Alcock.

In the past, when multiple comets were discovered by the same individual, group of individuals, or team, the comets' names were distinguished by adding a numeral to the discoverers' names (but only for periodic comets); thus Comets Shoemaker–Levy  1  to  9 (discovered by Carolyn Shoemaker, Eugene Shoemaker & David Levy). Today, the large numbers of comets discovered by some instruments makes this system impractical, and no attempt is made to ensure that each comet is given a unique name. Instead, the comets' systematic designations are used to avoid confusion.

Systematic designations

Original system

Until 1994, comets were first given a provisional designation consisting of the year of their discovery followed by a lowercase letter indicating its order of discovery in that year (for example, Comet 1969i (Bennett) was the 9th comet discovered in 1969). Once the comet had been observed through perihelion and its orbit had been established, the comet was given a permanent designation of the year of its perihelion, followed by a Roman numeral indicating its order of perihelion passage in that year, so that Comet 1969i became Comet 1970 II (it was the second comet to pass perihelion in 1970) [4]

Current system

C/2004 Q2, the second comet discovered in the second half of August 2004. It is also known as Comet Machholz after its discoverer Donald Machholz. Machholz-cutout.jpeg
C/2004 Q2, the second comet discovered in the second half of August 2004. It is also known as Comet Machholz after its discoverer Donald Machholz.

Increasing numbers of comet discoveries made this procedure awkward, as did the delay between discovery and perihelion passage before the permanent name could be assigned. As a result, in 1994 the International Astronomical Union approved a new naming system. Comets are now provisionally designated by the year of their discovery followed by a letter indicating the half-month of the discovery and a number indicating the order of discovery (a system similar to that already used for asteroids). For example, the fourth comet discovered in the second half of February 2006 was designated 2006 D4. Prefixes are then added to indicate the nature of the comet:

For example, Comet Hale–Bopp's designation is C/1995 O1. After their second observed perihelion passage, designations of periodic comets are given an additional prefix number, indicating the order of their discovery. [7] Halley's Comet, the first comet identified as periodic, has the systematic designation 1P/1682 Q1.

Separately to the systematic numbered designation, comets are routinely assigned a standard name by the IAU, which is almost always the name or names of their discoverers. [8] When a comet has only received a provisional designation, the "name" of the comet is typically only included parenthetically after this designation, if at all. However, when a periodic comet receives a number and a permanent designation, the comet is usually notated by using its given name after its number and prefix. [9] For instance, the unnumbered periodic comet P/2011 NO1 (Elenin) and the non-periodic comet C/2007 E2 (Lovejoy) are notated with their provisional systematic designation followed by their name in parentheses; however, the numbered periodic comet 67P/Churyumov–Gerasimenko is given a permanent designation of its numbered prefix ("67P/") followed by its name ("Churyumov–Gerasimenko").

Interstellar objects are also numbered in order of discovery and can receive names, as well as a systematic designation. The first example was 1I/ʻOumuamua, which has the formal designation 1I/2017 U1 (ʻOumuamua).

Relationship with asteroid designations

Sometimes it is unclear whether a newly discovered object is a comet or an asteroid (which would receive a minor planet designation). Any object that was initially misclassified as an asteroid but quickly corrected to a comet incorporates the minor planet designation into the cometary one. This can lead to some odd names such as for 227P/Catalina–LINEAR  [ it ], whose alternative name is 227P/2004 EW38 (Catalina-LINEAR), derived from the original provisional minor planet designation 2004 EW38.

In other cases, a known asteroid can begin to exhibit cometary characteristics (such as developing a coma) and thus be classified as both an asteroid and a comet. These receive designations under both systems. There are only eight such bodies that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson–Harrington (107P/Wilson–Harrington), 7968 Elst–Pizarro (133P/Elst–Pizarro), 60558 Echeclus (174P/Echeclus), 118401 LINEAR (176P/LINEAR), (300163) 2006 VW139 (288P/2006 VW139), (323137) 2003 BM80 (282P/2003 BM80), and (457175) 2008 GO98 (362P/2008 GO98).

Related Research Articles

Comet Astronomical object

A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

2060 Chiron Large 200km centaur/comet with 50-year orbit

2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt.

Comet Encke Periodic comet with 3-year orbit

Comet Encke, or Encke's Comet, is a periodic comet that completes an orbit of the Sun once every 3.3 years. Encke was first recorded by Pierre Méchain on 17 January 1786, but it was not recognized as a periodic comet until 1819 when its orbit was computed by Johann Franz Encke. Like Halley's Comet, it is unusual in its being named after the calculator of its orbit rather than its discoverer. Like most comets, it has a very low albedo, reflecting only 4.6% of the light its nucleus receives, although comets generate a large coma and tail that can make them much more visible during their perihelion. The diameter of the nucleus of Encke's Comet is 4.8 km.

In ancient times, only the Sun and Moon, a few stars, and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are discovered every year. Astronomers need to be able to assign systematic designations to unambiguously identify all of these objects, and at the same time give names to the most interesting objects, and where relevant, features of those objects.

Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated. Approximately 47 % of the more than 1,100,000 known minor planets remain provisionally designated, as hundreds of thousands have been discovered in the last two decades.

Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-type or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. David Jewitt defines a damocloid as an object with a Jupiter Tisserand invariant (TJ) of 2 or less, while Akimasa Nakamura defines this group with the following orbital elements:

Bielas Comet Disintegrated periodic comet

Biela's Comet or Comet Biela was a periodic Jupiter-family comet first recorded in 1772 by Montaigne and Messier and finally identified as periodic in 1826 by Wilhelm von Biela. It was subsequently observed to split in two and has not been seen since 1852. As a result, it is currently considered to have been destroyed, although remnants appeared to have survived for some time as a meteor shower, the Andromedids.

60558 Echeclus is a centaur, approximately 84 kilometers (52 miles) in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation 2000 EC98 (also written 2000 EC98). Research in 2001 by Rousselot and Petit at the Besançon observatory in France indicated that it was not a comet, but in December 2005 a cometary coma was detected. In early 2006 the Committee on Small Bodies Nomenclature (CSBN) gave it the cometary designation 174P/Echeclus. It last came to perihelion in April 2015, and was expected to reach about apparent magnitude 16.7 near opposition in September 2015.

11P/Tempel–Swift–LINEAR is a periodic Jupiter-family comet in the Solar System.

166P/NEAT Periodic comet with 51 year orbit

166P/NEAT is a periodic comet and centaur in the outer Solar System. It was discovered by the Near Earth Asteroid Tracking (NEAT) project in 2001 and initially classified a comet with provisional designation P/2001 T4 (NEAT), as it was apparent from the discovery observations that the body exhibited a cometary coma. It is one of few known bodies with centaur-like orbits that display a coma, along with 60558 Echeclus, 2060 Chiron, 165P/LINEAR and 167P/CINEOS. It is also one of the reddest centaurs.

118401 LINEAR, provisional designation 1999 RE70, is an asteroid and main-belt comet (176P/LINEAR) that was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) 1-metre telescopes in Socorro, New Mexico on September 7, 1999. (118401) LINEAR was discovered to be cometary on November 26, 2005, by Henry H. Hsieh and David C. Jewitt as part of the Hawaii Trails project using the Gemini North 8-m telescope on Mauna Kea and was confirmed by the University of Hawaii's 2.2-m (88-in) telescope on December 24–27, 2005, and Gemini on December 29, 2005. Observations using the Spitzer Space Telescope have resulted in an estimate of 4.0±0.4 km for the diameter of (118401) LINEAR.

Minor planet Astronomical object in direct orbit around the Sun that is neither a planet or a comet

A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Before 2006, the International Astronomical Union (IAU) officially used the term minor planet, but during that year's meeting it reclassified minor planets and comets into dwarf planets and small Solar System bodies (SSSBs).

Lost comet Comet which was not detected during its most recent perihelion passage

A lost comet is one which was not detected during its most recent perihelion passage. This generally happens when data is insufficient to reliably calculate the comet's location or if the solar elongation is unfavorable near perihelion passage. The D/ designation is used for a periodic comet that no longer exists or is deemed to have disappeared.

Comet Swift–Tuttle Periodic comet and parent of the Perseid meteors

Comet Swift–Tuttle is a large periodic comet with a 1995 (osculating) orbital period of 133 years that is in a 1:11 orbital resonance with Jupiter. It fits the classical definition of a Halley-type comet with an orbital period between 20 and 200 years. The comet was independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862.

40P/Väisälä Periodic comet with 10 year orbit

40P/Väisälä is a periodic comet that was discovered on February 8, 1939. Its orbit was determined on April 26, 1939. In 1994, the diameter of its nucleus was found to be 4.2 km, similar in size to that of Comet Encke.

<span class="nowrap">C/2014 UN<sub>271</sub></span> (Bernardinelli-Bernstein) Oort cloud comet

C/2014 UN271 (Bernardinelli-Bernstein), or simply 2014 UN271, or the Bernardinelli–Bernstein comet (nicknamed BB), is a large Oort cloud comet discovered by astronomers Pedro Bernardinelli and Gary Bernstein in archival images from the Dark Energy Survey. When first imaged in October 2014, the object was 29 AU (4.3 billion km) from the Sun, almost as far as Neptune's orbit and the greatest distance at which a comet has been discovered. During 2021, it will approach the Sun from a distance of 20.8 AU (3.1 billion km) to 19.5 AU (2.9 billion km) and will reach its perihelion of 10.9 AU (just outside of Saturn's orbit) in January 2031. The current 3-sigma uncertainty in the comet's distance from the Sun is ±60000 km. It is the largest Oort cloud comet discovered. It will not be visible to the naked eye because it will not enter the inner Solar System.


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