Comet Names
What do all those letters and numbers mean?
Table of Contents

We have been asked a few times what all of those letters and numbers in a comet's designation mean. Here is the official word from the IAU and the Minor Planet Center.

As shown below, a comet's official designation contains information about the orbit of the comet, and the year, month, and order of discovery. By convention the "common name" of the comet follows the designation in parentheses.

There are some exceptions, especially for well-known periodic comets. Frequently these are simply referred to by their MPC sequence number and name (e.g., 1P Halley, 19P Borrelly).

Official Sequence Type Year of Discovery Half-Month of Discovery Order of Discovery
Contents Optional A, P, C, X, or D e.g., 2010 A-H,J-X Number
Details An official number assigned and maintained by the Minor Planets Center1 for Periodic (type = P) comets only. A = An object re-desginated as an Asteroid, P = A periodic comet, C = A non-periodic comet, X = A comet for which an official orbit cannot be determined, D = An object that has disappeared Four Digit year, not always used for Periodic comets A = Jan. 1-15, B = Jan. 16-31, C = Feb. 1-15, etc., I and Z not used2 The order of discovery for the given half-month.
Example 1: 1P/1682 Q1 (Halley) 1 P (Periodic) 1682 Q (Second half of August) 1
Example 2: C/2010 X1 (Elenin) C (Non-Periodic) 2010 X (First half of December) 1


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