Every time there’s a comet in the inner solar system, as it makes it in news and media, the names are followed by some set of alphabets and numbers with a slash in there somewhere. Well, what if we told you, that, that string you see is the real name of the comet.
Human Names
Whenever we hear a comet (especially those that become visible to us using small telescopes), we know the comets through the names given to them. It was Halley’s Comet, Hale-Bopp, NEOWISE, SWAN and now Leonard.
These names are given to these comets depending upon the discovering instrument/observatory or person.
We are quite familiar with the story of Halley’s comet. It being discovered by Edmund Halley. Similarly Hale-Bopp was named after its discoverers, Alan Hale and Thomas Bopp and Comet Leonard is named after G. J. Leonard from the Mount Lemmon Observatory.
Similarly, comets like NEOWISE was named after the space telescope (instrument) that discovered it. NEOWISE stands for Near-Earth Object Wide-field Infrared Survey Explorer. While the space telescope is responsible for the discovery of several different planets, the sensational comet C/2020 F3 is known as comet NEOWISE due it being a naked-eye comet and grabbing media attention.
So when we say Comet NEOWISE, we mean C/2020 F3 and when we say Haley’s Comet, we mean 1P/Halley.
Technical Names
So cutting right to the chase, what do these numbers slashes and alphabets mean?
In the current day scenario, we find the comet’s technical name consists of an alphabet followed by a slash. What do these mean?
The First Letter
The first letter denotes the character. The following are the commonly assigned values:
- P/ : Periodic Comet. This identifier lets us know that the comet is periodic and will visit the inner solar system in the future. It also means that the comet has a closed orbit with an eccentricity less than 1.
- C/ : Non-Periodic Comet. An identifier that is an exact opposite of the P/ identifier, meaning the comet is not periodic and will never return to the inner solar system. It’s orbit is said to be open with an eccentricity greater than 1. This identifier can also mean that the comet may return to the solar system after a very long time (a span of centuries).
- I/ : Interstellar Comet. A comet with this identifier is said to have come from Interstellar space. This is usually determined by its orbital properties usually denoting a hyperbolic trajectory. See: 1I/2017 U1 ʻOumuamua.
- D/ : Disappeared/Lost Comet. A comet with the designation starting with D/ is a comet which has been observed once but could not be tracked further due to the lack of data.
- A/ : Asteroid/Possible Comet. These are objects that are identified as a possible comet, but leter turn out to be asteroids with comet like orbit.
- X/ : Unknown Comet. Like all things unknown, this symbol denotes comets whose orbit could not be determined and are not precisely observed.
The Year
The second part of the designation after the slash, is typically the year when the comet was discovered.
Eg. Comet Hale-Bopp which was observed in 1995 is designated C/1995 O1.
However, some comets with historical observations have this part in their designations skipped. Eg. Comet Haley with the Designation 1P/Halley.
Date/Period of observation
Following the year of discovery, we have a combination of a letter and number each that denotes the period of the year during which the comet was discovered. This follows the same logic as naming asteroids.
The number following the letter denotes the order of discover. Ex. Comet Machholz designated ‘C/2004 Q2’ was discovered by Donald Machholz on August 27, 2004. This was the second comet discovered during that second half of month August after C/2004 Q1, Hence the number 2 following Q.
Complete Name
Once the comet has been designated, the name of the comet is enclosed (usually) between brackets and that’s the full name of the Comet.
Now you know that when we say P/1 Haley is the designated name of Haley’s Comet, it is periodic comet discovered by someone named Haley.
and when you read C/2021 A1 Leonard, you know it is a 1st non-periodic comet discovered in 2021, during the first half of January by someone named Leonard.