Naming Stars

Many stars have common names while many more have designations that look like aviation parts, strings of numbers and letters. Who is to know NGC 188 isn’t a particular sized bolt used in a Boeing 747 wing frame? The fact is there are billions of stars and giving them common names would be a hopeless, and indeed pointless task. In the ancient times of stargazing names in Arabic were given, while Latin and Greek put in a later appearance. Many of the stars in those early times were associated with gods or myths. Quite a few of these are retained in the catalogues today. With the increasing ability of telescopes and modern astronomical equipment astronomers have been able to resolve fainter and more distant stars, even reporting that a “star” is actually a multiple of as many as four identifiable points of light.

The Orion Nebula
Also known by catalogue numbers M42 and NGC 1976 the Orion Nebula is captured here in both visible light and infra-red by Nasa’s orbiting Spitzer Telescope – 17th May 2016.

As the star maps have grown so the nomenclature has been augmented. For example, the Constellation Orion is named after the giant and handsome hunter in Greek mythology. Each star in this constellation is further identified using the Greek alphabet in lower-case, after the genitive. This was a system introduced in 1603 by Johann Bayer (1572 – 1625) and referred to in astronomy as the “Bayer letters”. This starts with ‘α’ (alpha) for the brightest star in the constellation, then β (beta) and so on until all the stars in the group are named. The last star, if there were to be as many as 24, would be called ω (omega). If there were more stars than this then Bayer had to resort to using the Roman letters, A-Z. Although this practice was later dropped you may come across stars so named in the early catalogues, such as P Cygni in the constellation Cygnus. Note that the prefix R-Z and double letters RR-ZZ are now used to identify variable stars (see separate entry).

In the case of Orion the brightest star, Rigel, is actually called Beta Orionis, but don’t let this confuse you. The problem is that Betelgeuse (Alpha Orionis) is a variable star and at the top of its pulse is just a tad brighter than Rigel! As a further example of the nomenclature we can find in Orion: Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis) and Mintaka (Delta Orionis).

In 1712 English astronomer John Flamsteed (1646 – 1719) introduced another system in which the stars were numbered in order of their right ascension (celestial co-ordinate) from west to east across their constellation. For example, 56 Cygni denotes a star that is 56th closest to the western side of the Constellation Cygnus.

There are other designations in the names of stars. For example, TTS refers to “T Tauri stars”, a class of variable stars named after the prototype star in the Constellation Taurus. They are young stars around ten million years old or so, having recently become visible as they begin to consolidate, shrink and approach their new life as a main sequence star.

As mentioned, the prefix R and upwards is used for variable stars. For instance, R Coronae Borealis is the prototype for hydrogen deficient, carbon rich supergiants that fade by several magnitudes at irregular intervals. They are quite rare and may be classed as R CrB, or just RCB after the prototype.

Other prefixes you may come across include “PSR” for pulsars, and “SN” for supernova.

In 1888 the New General Catalogue of Nebulae and Star Clusters (NGC) was published and later expanded to include the Index Catalogue (IC). These two are the leading catalogues for nebulae, star clusters and galaxies. They cover over 13 000 objects, all identified by either an NGC or an IC number.

Charles Messier (1730 – 1817) complied a catalogue of “non-comets”. He catalogued 110 in all and they are listed with the M prefix. His first true discovery was M3, a globular cluster in the Canes Venatici Constellation, and also labelled NGC 5272. The majority of his list covers open and globular clusters. However, M1 is actually a supernova remnant.  M27, the Dumbbell Nebula, is a planetary nebula, while M33 is a spiral galaxy called the Triangulum Galaxy. These examples also carry NGC or IC catalogue numbers.

So you can understand that the catalogues are a bit mixed up being applied to galaxies, nebulae and star clusters. M58 (also known as NGC 4579) is a normal barred spiral galaxy in the constellation Virgo. M31 (or NGC 224) is much better known as the Andromeda Galaxy.

It’s all academic really and I don’t suppose a common standard of naming the objects of the universe will ever arise. In any event one has to bear in mind that objects in the sky can have multiple designations depending on which listing you are using.

Letters of the Greek Alphabet
NameLower case

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By Nigel Benetton, science fiction author of Red Moon Burning and The Wild Sands of Rotar.

Last updated: Wednesday, 24th February 2021