Comet Names and Designations; Comet Naming and Nomenclature; Names of Comets (2024)

When a comet is discovered and confirmed, it is announcedby the Central Bureau for Astronomical Telegrams (CBAT)-- on behalf of the International Astronomical Union (IAU) --through its publications (the printed and electronicIAUCirculars, and occasionally also first via its electronic onlyCBETs). At the time of this announcement, it is usually given adesignation relating to the year of discovery, and (upon publication of thefirst orbit) also usuallya name that correspondsto the person, persons, or observing program that is creditedwith the discovery. (Sometimes naming is delayed for days or many weeksdue to debate over a proper name within the 16-member [as of July 2003] IAU Committeeon Small Bodies Nomenclature, which advises the CBAT on comet-naming issues.)Note that short-period comets are often recovered via prediction (or re-discovered accidentally) after having not been seen for some years,and if only making a second observed return to perihelion, such cometswill also get a provisional year-and-letter/number designation forthe current date of recovery (with a permanent-number designation usuallyto follow soon thereafter).

While comets dating back to Charles Messier of Parisin the late 18th century are now listed in catalogues as havingnames, the situation regarding recognized naming of cometshas been very complicated and non-uniform over the last coupleof centuries. The first definite comet to be credited internationallyas "belonging" to an astronomer was not until after 1759, whenthe comet that had been predicted by Edmund Halley in 1705to return in a few decades (being the same comet that had been seen in 1607and 1682) was indeed re-discovered in 1758. And, indeed,Halley's comet is the most famous of all comets today (though thename "Halley" is pronounced with a short "a", so that it rhymeswith the English word "alley", not like the long "a" in"Haley" of "Bill Haley and the Comets" fame). But inthe 19th century, it was typical to follow the example ofHalley's comet whereby (in general) comets were given names onlyafter they were observed at their second apparition (or returnto perihelion), meaning that most long-period comets werereferred to only by a number and year (as the third comet ofa given year) or by a year-and-letter or year-and-Roman-numeraldesignation. Beginning in the middle of the 19th century, astronomicalpublications sometimes gave names of discoverers in titles referringto observations of a given comet, but those names were usually put inparentheses: comet designations were given primacy, the namesbeing given in parentheses (if at all) after the year designation.This practice of referring only to multiple-apparition comets by thediscoverers' names, and to single-apparition comets by the designation,continued until the second world war (1940s).

In the late 19th century and early 20th century, some astronomersbegan to refer to short-period comets carrying the same discoverer name(e.g., Tempel, Brooks, Schwassmann-Wachmann, etc.) -- such as the first andsecond Tempel comets, or Tempel I and Tempel II, or Tempel (1) and Tempel (2), and finally Tempel 1 andTempel 2. For the last 50 years or so, this practice of using suffixedArabic numerals has been widely employed, but with the adoption in the 1990sof a new designation scheme (with the practical scheme of permanent numberingsof multi-apparition short-period comets), such numerals are redundantand unnecessarily complicated. Indeed, beginning in 1995, numerals wereno longer added to newly discovered comets, and with the change in nameof "Shoemaker 2" to "Shoemaker-LINEAR" in late 2000 upon its accidentalrediscovery, there is a gap leaving short-period comets named "Shoemaker 1","Shoemaker 3", and "Shoemaker 4". (The acronym "LINEAR" stands for the"Lincoln Near-Earth Asteroid Research" project, operated by the LincolnLaboratory of the Massachusetts Institute of Technology.)Thus, at the end of 2000, the ICQ adoptedthe practice of eliminating the suffixed numerals to comet names; this doesmean, however, that permanent numbers or year/letter/numberdesignations must be used with the name (of course, it is sufficient touse the permanent numbers or designations alone without the name, but notvice versa). The IAU adopted a policy of *optionally* including orexcluding suffixednumerals to comet names when it approved the new set ofcomet-namingguidelines in March 2003. Thus, the Minor Planet Center and theCentral Bureau for Astronomical Telegrams also no longer use comet-namesuffixed numerals. (While a few people who have dealt a lot with cometsover the last several decades will wish to continue using the redundantsuffixed numerals for nostalgic reasons, such use will fade intooblivion during thenext generation of astronomers -- so one might as well stop using themnow and concentrate instead on the more logical prefixed numerals. Thiswill make it easier on astronomers of the future, who will soon bewondering what the suffixed numerals stood for in the "old"literature, as the old suffixed numerals fall rapidly into dis-use.)

While it is assumed by many that all comets are named for theirdiscoverers, this is not strictly true. Some comets discovered long ago(1P/Halley, 2P/Encke, 27P/Crommelin) were named for astronomers who actuallyworked arduosly on their orbits to show that observations at different"apparitions" were one and the same comet. Others in the past have beenerroneously named for non-discoverers due to lack of accurate information.For comets that do not receive the names of the individual people involved,it is perhaps better thought of as "labelling" such comets (rather than"naming"). Some comets, then, have been "labelled" for spacecraftthat have detected them (including hundreds of comets labelled "SOHO" forthe sun-orbiting coronagraph spacecraft that has imaged many tiny comets veryclose to the sun that are usually invisible from the ground). Today thereare numerous professional CCD survey programs that scan the sky most clearnights of each month looking for near-earth objects (NEOs), which are usuallyminor planets (or more rarely, comets) that pass -- or can pass --within about 0.1 AU of the earth. Convention is now that most cometsfound by such surveys, which each employ numerous people, are labelled/namedusually (but not always) for the survey program name; thus, we havesome 117 comets labelled "LINEAR" as of Sept. 2003, 35 comets labelled for"NEAT", nine comets labelled for "LONEOS", seven comets labelled "Spacewatch",four comets labelled "Catalina", and three comets labelled "Tsuchinshan",Sometimes two-member teams will get both names on a comet, but twonames is a firm limit for such teams; occasionally a single astronomerfrom a large-survey program will be the observer, discoverer, andcommunicator of a new comet discovery, and such individual names are insuch cases sometimes allowed to go with the comet rather than the team name.The general rule today is that, once a comet has been announced widely via theInternet (WWW or e-mail), it is no longer eligible for additional namesto be added due to "independent discoveries". Some comets have neverbeen named, including most comets from the 18th century and earlier, andmany other comets discovered years after they were visible (from photographs,for example) and many comets that have no possible orbit determinations(due to few available observations).

In the 1930s and 1940s, it became customary onIAU Circulars to put the discoverer's name after the word "Comet",with the year designation given parenthetically. But in 1995,with the official IAU change to anewcomet-designation scheme that moreclosely resembles the minor-planet designation scheme in placefor most of the 20th century (having both "provisional unnumbered" and"permanent numbered" designations), the CBAT and its allied Minor PlanetCenter reverted to the standard19th-century format of giving year designations first withnames (if at all) parenthetically. This is because scientistsdealing with a lot of data in computer form will invariably wantto use a designation only for a given comet in a formthat will have a uniform number of sortable columns. (It may have madesome sense to refer to comets by name when there were not so many cometsaround, but nowadays with so very many comets discovered every year, itis really easier and more certain and safe to refer to comets by theirdesignation primarily and by their names in a more secondary manner.)Thus, comets are assigned provisionally a year-letter-number designationthat specifies the year, half-month, and sequence within thathalf-month of discovery (the year and half-month/sequence-numberbeing separated by a single space) -- and this is preceded bya "C/" for single-apparition comet or a "P/" for either amultiple-apparition comet or a single-apparition comet withorbital period less than about 30 years. (Sometimes a "D/" isused for short-period comets that cannot be predicted accurately andare essentially considered lost, due to limited observations.)The permanent numbers are given in chronological (historical) orderin which the comets are confirmed as returning to perihelion twoor more times, and are given as "nnnP" or "nnnP/name", wherennn is the number.

Many people use a popular approach and use only the name(and not the designation) when referring to a comet. It isnatural in everyday speech (discussions between two or three people),when talking about a given comet, to refer to it by name alone, asthere will usually not be any ambiguity amongst those partaking inthe discussion (and one can ask the other if not clear). But in formaltalks or lectures and in print, one should always use the comet'sdesignation (with or without the name) for absolute clarity.Even scientists get sloppy in thismanner in the literature, and one will find that few editorsseem to understand the usefulness of maintaining a unifiedapproach to comet nomenclature in a journal or conferenceproceedings -- so that one finds the authors (and, by default,the editors) carelessly using their own personal preferences(which may number a dozen different possible ways of referringto a comet!) in their own writings about a comet or comets.We strongly discourage this sloppiness and encourage all writers(especially scientists, but also regular journalists) tofollow the official CBAT/MPC/ICQ format for comet nomenclature,as is uniformly visible on all of our web pages and all ourpublications without exception. Thus, we have unnumbered,single-apparition comets like "C/1995 O1 (Hale-Bopp)" and numberedcomets like "1P/Halley", which can also be called comet "1P/1982 U1 (Halley)"for its most recent apparition, or simply "1P (Halley)" or even just "1P".This last term is often useful for use in tables and graphs/charts in particular,especially in the case of a comet with a really long name, where (forexample) "57P" alone may be preferable to "57P/du Toit-Neujmin-Delporte"when mentioned many times in a given paper (of course, the full designationand name should be given at the beginning of any paper on a particularcomet, for clarity). [Note that such unofficial abbreviations as "d-N-D"or "57P/d-N-D" are to be avoided, though a few scientists have a habitof using such awkward shorthand.]

In the case of discussing pre-1995 comets, itis recommended to use both the new-style and old-style designations whenreferring to such comets in text, for the convenience of readers who mayeither be familiar with older designations or who may be consulting olderliterature containing only the old-style designations. Thus, comet"C/1973 E1 (Kohoutek) = 1973 XII = 1973f", or "C/1973 E1 (Kohoutek; O.S.1973 XII = 1973f)".

Further reading:

Green, D. W. E. (1997). ICQ Guide to Observing Comets, p. 11.

Marsden, B. G. (1995).ICQ17, 3.

Index to the CBAT/MPC/ICQ pages.