The designation of comets

The designation of comets is a complex topic in which many changes have occurred over time. Until the mid-18th century, comets were simply designated by the year of their occurrence. The first to receive a different name was Halley’s comet, so named in 1759 by La Caille (1713-1762). Then, comets often took the name of their discoverer, or of the person who established their period, if periodic; this was the case of comets Encke and Lexell.

In the 20th century, a provisional designation indicated the year of their discovery followed by a lowercase letter giving the order of this discovery in that year. Then a final designation was given after about two years, including the year of perihelion passage followed by a serial number in Roman numerals. Thus, comet West, discovered in 1975 and which passed at perihelion on February 25, 1976, was first called 1975n and later 1976 VI. This system had drawbacks. The number of discovered comets increasing rapidly, it depleted the letters of the alphabet and one had to start the alphabet again and add a number: the 27th comet of year xxxx was affected by the provisional designation xxxxa1. Sometimes comets are discovered after perihelion passage, which leads to inconsistencies. Finally, some short-period comets are observable throughout their orbit, making unfounded object their provisional designation.