How Asteroids And Supernovae Are Named

How Asteroids and Supernovae Are Named

As most people know, constellations, dwarf planets and natural satellites are commonly named using a mythology theme. Andromeda, Haumea and Enceladus are examples – but what about the millions of other objects? Here’s how they number Asteroids and Supernovae.


Asteroids are all indexed with consecutive numbers in the order of their discovery. With half a million asteroids indexed, only 22,000 have names. Asteroids which have no name are just given a number e.g. Asteroid 487901.

Naming also uses mythology for some objects, such as 1 Ceres and 2 Pallas. However, many asteroids are named after worthy people, including astronomers like our good friend Prof. Fred Watson (Asteroid 5691 Fredwatson).

Asteroid 1 Ceres is also a dwarf planet (Credit NASA Dawn Mission)
Asteroid 1 Ceres is also a dwarf planet (Credit NASA Dawn Mission)

Other names are a mixture of fiction, geographic features and locations, observatories and whatever seems to take their fancy.

For many years the discoverer retained the privilege of naming the asteroid him or herself but nowadays the authority rests with the Minor Planet Centre, although the discoverer may submit a proposed name.

My two favourites asteroids are 920 Rogeria and 9739 Powell but unlike Fred, I cannot claim any credit.

Rogeria was a woman’s name chosen by the prolific discoverer Karl Reinmuth, who is credited with discovering 395 asteroids between 1914 and 1957. He named a lot of them after women, so he must have been a popular guy with the ladies!

Asteroid 9739 Powell was named after James Powell, a geology professor at Oberlin College, US.


I recently imaged a supernova for the first time (in M61) and went looking for its designation: SN 2020 jfo.

Wait a minute, I thought, what does “jfo” mean?

When it comes to cataloguing huge numbers of sky objects, names generally consist of alphanumeric numbering systems with some creative methodology.

M61 galaxy with supernova SN 2020 jfo
 Image © Roger Powell
2020-05-24 M61 galaxy with SN 2020 jfo
Image © Roger Powell

Historical supernovae are named after the year in which they occurred, for example SN 1572 occurred in the year 1572. There were not many supernovae observed until the advent of big telescopes, which brought intergalactic supernova within our reach. So changes to the naming system occurred in 1885 and 1988.

First one and then two capital alphabet numbers were added, so the first twenty-six supernovae of the year were suffixed A to Z, (SN 1885A to SN 1885Z) then the twenty-seventh and twenty eighth discoveries became SN 1986AA to 1988ZZ etc.

This allowed a maximum of 26×26=676 listings but the number of discoveries continues to increase, so since 2016, a lower case three-character designation system was introduced.

The first 26 supernovae of each year are still named using the same sequence, e.g. SN 2020A (with capital letters) and after SN 2020Z has been reached, the numbering system changes and pairs of lower case letters are employed instead: aa, ab, and so on. If that sequence runs out, a third letter is added.

Hence the M61 supernova SN 2020 jfo which I imaged is the 690th supernova discovery so far this year. (26×26) + 14 = the 690th supernova of 2020.


This article first appeared in Prime Focus Magazine:

Prime Focus Magazine - June 2020
My article page.
Prime Focus Magazine – June 2020


  1. Thank you for the info, Roger. I like learning how discoveries are named. It’s all very logical.


    1. Thanks, Fran. I’m going to write a future article on how some other object names are allocated (e.g. star TYC 2002-1055-1). I have no doubt there is logic involved but I haven’t discovered it yet!


  2. Fascinating! What makes the difference between which asteroids receive names versus those that don’t? Are previously unnamed asteroids ever named later or do they stay numbers if not named on discovery?

    Liked by 1 person

    1. My understanding is that asteroids can be named by the Minor Planet Centre at their own convenience – but normally well after discovery. They would be working with limited resources. Naming 22,000 of them is not a bad effort!
      The discoverer submits proposed names for approval but there does not seem to be any mechanism for others to propose names, which is a pity.

      Liked by 1 person

      1. Thank you! I was wondering. I’ve seen some of the lists of asteroid names and that got me curious about the process. It is a pity more people can’t submit names, but I suppose the Minor Planet Centre would be swamped with ideas if anyone could name an asteroid. 😅

        Liked by 1 person

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