Halley’s Comet may be one of the most famous comets, but these moving bodies within our solar system are much more frequent than 75years between appearances. The beautiful tail that often captures the eye and imagination of astronomers and dedicated photographers alike is a clump of cold rock and ice that’s warmed into water vapor as it passes the sun. Billions of comets are believed to exist within the solar system, with only a tiny fraction coming close enough to the earth each year to be observed by either the naked eye or highly-trained scientists with their eyes firmly planted heavenward. It only makes sense that when someone finds a comet that they’d want to be able to christian it with a name. However, if John Smith discovers a comet today and expects it be named Smith’s Comet, he may be surprised with the official name designation he actually receives.

Comet Naming Guidelines

The guidelines for naming a comet have changed significantly over the years. Initially, a comet was named after the person who discovered it, as in Halley’s Comet named after English astronomer and mathematician Edmond Halley. A systematic naming of comets remained in effect until 1994. Under this system, a comet was named based on its provisional designation of the year of its discovery. This was followed by a lowercase letter indicating the order of discovery of comets the particular year a comet was reported for naming. Today, however, a comet is named according to a complex system created by the International Astronomical Union. The result is names like C/2012 S1 (ISON) and C/2013 R1 (Lovejoy) rather than Caesar’s Comet or Donati’s Comet.

The First Letter of the Type of Comet

The first letter of the name of a “new” comet is the first letter of the type of comet that it is. The four basic types of comets recognized by the International Astronomical Union are:

• C – for comets on paths higher than the sun’s escape velocity (usually a single pass)
• P – for comets on a specific periodic orbit (it’s known when they will come back)
• D – for comets that disintegrate or become lost after their initial discovery
• X – for comets with no known orbit (usually comets discovered before accurate orbit calculations existed)

The Year and Half-month of When the Comet Was Discovered

The second part of the name of a comet is the year it was discovered along with the specific half-month designation. Half-month designations for the purpose of naming a comet are based on the letters of the alphabet in order. Each month is given two letters to denote a half of the month. The half-months for January, for example, are “A” and “B” while February would be “C” and “D” and so-on throughout the year.

The Last Names of the First Two People to Report the Comet

The final part of the equation is the last names of the first two people/groups to have reported the comet. At one point, the name of a comet could extend to at least three people to have discovered it. The three names were then hyphenated. Today, the name of a comet is limited to the first two people to officially report the comet to the International Astronomical Union. In some cases, there may be disputes over who reported what first. However, that doesn’t appear to be much of an issue since a person reporting a newly discovered comet first or second is given credit unless their proof of discovery is discredited or flawed in some way.

Using the Name of An Observatory or Group

These days, many comets are officially reported by an observatory or other specific scientific agency as a whole rather than by a single individual. In this case, the name of the observatory or agency is used in place of the last name. Using the comet name C/2012 S1 (ISON) as an example, it can be determined that this comet made a single pass before heading out into the vastness of space not likely to return again. It was discovered in the second half of September of 2012. Since the discovery was reported by a group (Russian International Scientific Optical Network observatory, in this case), the group name replaces the part of the comet name that would be held by an individual discoverer.


While the current rules for naming a comet are pretty much standard, there are exceptions to the rule. The most common exception is when a comet that was previously known to exist is determined to be a comet that returns on a regular basis rather than a one-time sighting as was initially reported, or at least observed at some point. While Halley is given credit for the comet that bares his name, for instance, that particular comet is believed to have been observed as far back as 240 BC. Technically, it’s still possible for a comet to be designated one way after its initial discovery and proven to be another type of comet a later point in time.

Get Started By Reporting Your Comet

The very first step in reporting what is believed to be a new or undiscovered comet is to report it to the International Astronomical Union. Aside from this being the first step towards obtaining naming rights, officially reporting a comet allows the discovered to determine whether or not they really have an undiscovered comet. It is possible that a comet could have already been reported by at least two individuals or it may already have a name. If everything checks out, the process of assigning a name gets underway.


Cynthia Lopez