As of this writing, there are 3,635 comets named SOHO, over 300 comets named LINEAR, some 179 comets named PANSTARRS, 82 comets named McNaught, 62 comets named NEAT, and so on.
Except for the comets discovered by Scottish-Australian astronomer Robert H. McNaught (1956-), all of the above comets were discovered by various automated surveys.
SOHO = Solar and Heliospheric Observatory (spacecraft)
LINEAR = Lincoln Near-Earth Asteroid Research
Pan-STARRS = Panoramic Survey Telescope and Rapid Response System
NEAT = Near-Earth Asteroid Tracking
How do we distinguish between comets having the same name? Each has a separate comet designation. The first Comet LINEAR has a designation of P/1997 A2, and the most recent Comet LINEAR has a designation of C/2017 B3.
A comet designation starts with one of the following prefixes:
P/ – a periodic comet (orbital period < 200 years or confirmed observations at more than one perihelion passage)
C/ – non-periodic comet (orbital period ≥ 200 years and confirmed observations at only one perihelion passage)
X/ – comet for which no reliable orbit could be calculated (generally, historical comets)
D/ – a periodic comet that has disappeared, broken up, or been lost
A/ – an object that was mistakenly identified as a comet, but is actually a minor planet (asteroid, trans-Neptunian object, etc.)
I/ – an interstellar object that did not originate in our solar system
This is then followed by the year of discovery, a letter indicating the half-month of discovery, followed by the numeric order of discovery during the half-month.
So, we can see that the first Comet LINEAR, P/1997 A2, is a periodic comet discovered in 1997, between January 1 and January 15 of that year, and it was the second comet to be discovered during that period of time. After the second perihelion passage, P/1997 A2 (LINEAR) was subsequently given the periodic comet number prefix of 230, so the full designation for this comet is now 230P/1997 A2 (LINEAR).
Likewise, the most recent Comet LINEAR (at the time of this writing), C/2017 B3, is a non-periodic comet discovered in 2017 between January 16 and January 31, the third comet discovered during that period of time.
Interestingly, if different periodic comets have the same name, they are sequentially numbered. Perhaps the most famous example is Comet Shoemaker-Levy 9 that broke up and crashed into Jupiter during July 1994. There are a total of nine periodic comets named Shoemaker-Levy. They are:
192P/1990 V1 Shoemaker-Levy 1
137P/1990 UL3 Shoemaker-Levy 2
129P/1991 C1 Shoemaker-Levy 3
118P/1991 C2 Shoemaker-Levy 4
145P/1991 T1 Shoemaker-Levy 5
181P/1991 V1 Shoemaker-Levy 6
138P/1991 V2 Shoemaker-Levy 7
135P/1992 G2 Shoemaker-Levy 8
D/1993 F2 Shoemaker-Levy 9
However, four additional non-periodic comets were discovered by the Carolyn & Gene Shoemaker and David Levy team. They have not received a numeric suffix and are all called “Comet Shoemaker-Levy”:
C/1991 B1 Shoemaker-Levy
C/1991 T2 Shoemaker-Levy
C/1993 K1 Shoemaker-Levy
C/1994 E2 Shoemaker-Levy
This strikes me as a bit strange. Why afford a numeric suffix to a comet name only when it is a periodic comet? Why not give all comets named “Shoemaker-Levy” a numeric suffix. Normally, we would number them all in order of discovery, but since the nine periodic comets have already received a number, we would have to number the four non-periodic comets as C/1991 B1 (Shoemaker-Levy 10), C/1991 T2 (Shoemaker-Levy 11), C/1993 K1 (Shoemaker-Levy 12), and C/1994 E2 (Shoemaker-Levy 13).
I would like to see all comets, both periodic and non-periodic, receive a numeric suffix to their names whenever there is more than one. So, instead of Comet LINEAR we would have Comet LINEAR 1, Comet LINEAR 2, Comet LINEAR 3, and so on.
By the way, the days of amateur astronomers discovering a new comet will probably soon come to a close. Though this is a little sad, it does tell us that the entire sky is being monitored much more closely than in the past, by a number of automated surveys. And that is a good thing, because we will be much less likely to miss anything “new” in the sky.
None One of the comets this year (so far) have has been discovered by amateurs.
UPDATE – November 20, 2018: California amateur astronomer and prolific comet hunter Don Machholz, along with Japanese amateur astronomers Shigehisa Fujikawa and Masayuki Iwamoto, independently discovered a new comet on November 7. The new long-period comet has been named C/2018 V1 (Machholz-Fujikawa-Iwamoto). Remarkable!
Here is the current tally of comet discoveries (or recoveries) this year:
Pan-STARRS (Panoramic Survey Telescope and Rapid Response System)
C/2018 A1 (PANSTARRS)
364P/2018 A2 (PANSTARRS)
C/2018 A4 (PANSTARRS)
P/2018 A5 (PANSTARRS)
C/2018 F4 (PANSTARRS)
P/2018 H2 (PANSTARRS)
P/2018 L1 (PANSTARRS)
P/2018 L4 (PANSTARRS)
P/2018 P3 (PANSTARRS)
P/2018 P4 (PANSTARRS)
C/2018 P5 (PANSTARRS)
372P/2018 P6 (McNaught) [recovery of P/2008 O2]
ATLAS (Asteroid Terrestrial-impact Last Alert System)
C/2018 A3 (ATLAS)
C/2018 E1 (ATLAS)
C/2018 K1 (Weiland) [H. Weiland, ATLAS]
C/2018 L2 (ATLAS)
C/2018 O1 (ATLAS)
MLS (Mt. Lemmon Survey)
C/2018 A6 (Gibbs) [A.R. Gibbs, MLS]
C/2018 B1 (Lemmon)
P/2018 C1 (Lemmon-Read) [M.T. Read, Spacewatch, Kitt Peak]
C/2018 C2 (Lemmon)
C/2018 EF9 (Lemmon) [originally classified as an asteroid]
C/2018 F1 (Grauer) [A.D. Grauer, MLS]
C/2018 F3 (Johnson) [J.A. Johnson, MLS]
C/2018 KJ3 (Lemmon) [originally classified as an asteroid]
P/2018 L5 (Leonard) [G. Leonard, MLS]
C/2018 R3 (Lemmon)
C/2018 R5 (Lemmon)
SONEAR (Southern Observatory for Near Earth Asteroid Research)
C/2018 E2 (Barros) [Joao Barros, SONEAR]
NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer)
C/2018 EN4 (NEOWISE) [originally classified as a Centaur asteroid]
C/2018 N1 (NEOWISE)
366P/2018 F2 (Spacewatch)
CSS (Catalina Sky Survey)
367P/2018 H1 (Catalina)
C/2018 M1 (Catalina)
C/2018 R4 (Fuls) [D.C. Fuls, CSS]
NEAT (Near-Earth Asteroid Tracking)
368P/2018 L3 (NEAT)
370P/2018 P2 (NEAT)
ASAS-SN (All Sky Automated Survey for SuperNovae)
C/2018 N2 (ASASSN)
OGS (ESA Optical Ground Station)
369P/2018 P1 (Hill) [recovery of P/2010 A1]
371P/2018 R1 (LINEAR-Skiff) [recovery of P/2001 R6]
373P/2018 R2 (Rinner) [Jean-Francois Soulier, Maisoncelles, and Krisztian Sarneczky, University of Szeged, Piszkesteto Station (Konkoly), independently recovered P/2011 W2]
374P/2018 S1 (Larson) [Krisztian Sarneczky and Robert Szakats, University of Szeged, Piszkesteto Station (Konkoly), recovered P/2007 V1]
375P/2018 T1 (Hill) [Krisztian Sarneczky, University of Szeged, Piszkesteto Station (Konkoly), recovered P/2006 D1]