List of periodic comets
Periodic comets are defined for these purposes as those
comets having orbital periods of less than 200 years (also known as "short-period comets") "or" which have been observed during more than a single perihelionpassage (e.g. 153P/Ikeya-Zhang). (Note that "periodic comet" is also sometimes used to mean any comet with a periodic orbit, even if greater than 200 years.)
Periodic comets receive a permanent number prefix usually after the second perihelion passage, which is why there are a number of unnumbered periodic comets, such as
P/2005 T5 (Broughton).
In nearly all cases, comets are named after their discoverer(s), but in a few cases such as
2P/Enckeand 27P/Crommelinthey were named for a person who calculated their orbits (the orbit computers). The orbits of periodic comets are especially tricky to calculate because of all the possible perturbations from every planet, and in the days before electronic computers some people dedicated their entire careers to this. Even so, quite a few comets were lost because their orbits are also affected by non-gravitational effects such as the release of gas and other material that forms the comet's coma and tail.
Periodic comets sometimes bear the same name repeatedly (e.g. the nine Shoemaker-Levy comets or the twenty-three NEAT comets); the IAU system distinguishes between them either through the number prefix or by the full designation (e. g. 181P and 192P are both "Comet Shoemaker-Levy"). In the literature, an informal numbering system is applied to periodic comets (skipping the non-periodic ones), thus 181P and 192P are known as Comet Shoemaker-Levy 6 and Comet Shoemaker-Levy 1, respectively. Non-periodic Shoemaker-Levy comets are interleaved in this sequence:
C/1991 B1between 2 and 3, C/1991 T2between 5 and 6, C/1993 K1and C/1994 E2after Shoemaker-Levy 9.
In comet nomenclature, the letter before the "/" is either "C" (a non-periodic comet), "P" (a periodic comet), "D" (a comet which has been lost or has disintegrated), "X" (a comet for which no reliable orbit could be calculated —usually historical comets), or "A" for an object that was mistakenly identified as a comet, but is actually a
Some lists retain the "C" prefix for comets of periods larger than about 30 years until their return is confirmed (e.g. [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2008+E1 C/2008 E1 (Catalina)] vs. [http://pdssbn.astro.umd.edu/comet_data/periodic_comets.html P/2008 E1 (Catalina 9)] ).
Numbered periodic comets
Unnumbered periodic comets
* [http://www.cfa.harvard.edu/iau/lists/PeriodicCodes.html Minor Planet Center Periodic Comet Numbers]
* [http://www.cfa.harvard.edu/iau/CometDes.html Converter between old-style and new-style comet names]
* [http://www.cometography.com/periodic_comets.html Cometography.com Periodic Comets]
* [http://www.aerith.net/comet/catalog/index-periodic.html Seiichi Yoshida's Comet Catalog]
* [http://pdssbn.astro.umd.edu/comet_data/periodic_comets.html Periodic comets on the Planetary Data System Small Bodies Node]
* [http://cfa-www.harvard.edu/iau/lists/LastCometObs.html MPC: Dates of Last Observation of Comets] (periodic and non-periodic)
List of non-periodic comets
Minor Planet Center
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