Exploring the Planets

Comet Names

Comets are given unique designations that include the year and half-month of discovery, with the half-month given with upper-case letters (A = Jan. 1-15, B = Jan. 16-31, C = Feb. 1-15, etc.; letters I and Z are not used). A numeral (1, 2, 3, etc.) follows the letter within the half-month. Thus, three comets discovered in the first half of March 2002 would be known as C/2002 E1, C/2002 E2, and C/2002 E3. A "P/" is used instead of "C/" when the comet has an orbital period under 30 years. Once a "periodic" or "short-period" comet has been observed to return to perihelion twice, it is given a permanent number that precedes the comet name (thus, 1P/Halley, 2P/Encke, 152P/Helin-Lawrence, etc.). This designation scheme replaced in 1995 Roman numerals. In the 19th century, astronomers sometimes referred also to returning short-period comets with names that reflected the discoverers (beginning in the 18th century with Halley's comet), and during the 20th century, comet names began to be very widely used in addition to the designations. The official use now is to give the comet's designation, followed by its name parenthetically; thus, comet C/1995 01 (Hale-Bopp). Permanently numbered periodic comets are usually written with the number and the name; thus, 1P/Halley, or 19P Borrelly.

Comet discoveries are reported (usually by e-mail) to the Central bureau for Astronomical Telegrams (so-called for historical reasons, when telgrams used to be used), which is operated for the International Astronomical Union by the Smithsonain Astrophysical Observatory in Cambridge, Massachussetts. Before comets are designated and announced by the Bureau, they must be comfirmed, and this usually involves observations by an experienced second observer at a second observing site.