Naming Stars

As individual naming is not exactly practical for a large number of stars, a more schematical nomenclature is needed. Several of these schemes have been introduced, and a number of them is still in use today (see our list of bright stars for examples).

The earliest naming system which is still popular was introduced by Johann Bayer in his Uranometria star catalog of 1603. As many predecessors and successors, he used constellations to identify stars within them. To distinguish the stars in each constellation, he labelled them with Greek letters, and approximately in the order of their (apparent) brightness, so that the brightest star was labelled Alpha, the second brightest Beta, an so on. For example, the brightest star in Cygnus the Swan is Alpha Cygni (note the use of the genitive of the Latin constellation name) which is also called Deneb, or the brightest star in Leo the Lion is Alpha Leonis, also called Regulus. Misestimates and other irregularities are the reasons why this is only an approximate scheme: For example, the brightest star in Gemini the Twins is Beta Geminorum (Pollux) while Alpha Geminorum (Castor) is only the second brightest star of the constellation. Unfortunately, the Greek alphabet has only 24 letters, and many constellations contain many more stars, even if the naming is restricted to those visible to the naked eye; Bayer employed low case letters a .. z and then upper case letters A .. Z for the stars number 25 to 50 and 51 to 76 in each constellation, respectively.

Another popular naming scheme is the use of the so-called Flamsteed numbers, which were introduced in the catalog Historia Coelestis Britannica which had been compiled by John Flamsteed (1646-1719), and was published unauthorised in 1712 after editing by Edmond Halley (1656-1742); Flamsteed's own corrected publication of this work did not contain the numbers, btw. In this scheme, stars of each constellation are numbered in the order of their Right Ascension (for example: 61 Cygni). Because the numbers were taken from the preliminary, error-rich version of the catalog, there are many deviations from the desired order in the numbers.

Other schemes have been introduced, e.g. one by Gould which is occasionally referenced as, e.g., 38G Puppis. But these are no more very popular now.

Fainter stars are normally identified by their numbers in some catalog, such as the Bonner Durchmusterung (BD), the Henry Draper Catalog (HD) or the General Catalog (GC) of Boss, for example, BD +75 deg 752 (star number 752 in the Declination zone +75 deg) = HD 197433 = GC 28804. BD is supplemented by the Cordoba Durchmusterung (CD) and the Cape Durchmusterung for southern stars. Other lists commonly used are the Smithonian Astrophysical Observatory Catalog (SAO), the Bright Star Catalog (Harvard Revised Photometry, HR), or the Positions and Proper Motions Catalog (PPM); find more e.g. in our list of Star Catalogs. An example with a lot of names is Betelgeuse = Alpha Orionis = HR 2061 = BD +7 1055 = HD 39801 = SAO 113271 = PPM 149643, at RA 05:55:10.306, Dec +07:24:25.35 (2000.0), the bright red supergiant in Orion.

Components of binary or multiple stars are usually labelled by capital roman letters, following the designation of the star, may this be a common name, Bayer or Flamsteed designation, or a catalog number. For example, the brightest star in the sky, Sirius, has a white dwarf companion which is identified each of the following designations: Sirius B, Alpha Canis Majoris B, or e.g. HD 48915 B.

A notable nomenclature scheme has been developed for variable stars, by Friedrich Wilhelm Argelander in 1862. He proposed to reserve the letters "R" to "Z" for naming the variable stars in each constellation, as Bayer's naming scheme had left these over in each case (and some constellations had a star "Q" in this scheme, e.g. Centaurus, Puppis and Vela). At that time, the 9 possible names per constellation seemed more than enough, as the number of known variables was small. However, it turned out that it was completely insufficient, and thus the scheme was first extended to two-letter designations, then even to numbers. Eventually, variables are named as follows: The designation of variables consists of one or two letters and constellation name (such as U Sagittarii or RR Lyrae) or a number preceded by "V" and the constellation name (e.g., V 1500 Cygni). In each constellation, the first variable discovered is assigned the letter "R" and the genitive of the constellation name, e.g., "R Andromedae" (a long period variable), the second one is "S" (e.g., "S Andromedae" is the supernova which occured in the Andromeda galaxy, M31), and so on up to "Z" for number 9; then the tenth variable is assigned "RR", followed by "RS" etc up to "RZ", "SS" (not "RS"), etc up to "SZ", and so on up to "YY", "YZ", "ZZ", and then "AA", "AB", etc to "AZ", "BB" to "BZ", up to "QQ" to "QZ" (where the letter "J" is not used to avoid confusion with the letter "I"). Counting, this scheme provides 334 designations for each constellations, and variables starting from number 335 are designated "V 335", "V 336" etc. Those already assigned a Bayer designation are not given a new name according to this scheme (such as Delta Cephei, Beta Lyrae, Beta Persei [Algol], or Omicron Ceti [Mira]).

Variable stars are classified by types which are then named after one typical representative, e.g., "Mira stars", "RR Lyrae stars", or "Delta Cephei stars" (often called "Cepheids" in deviation from the usual scheme).

Special names are assigned for new novae and supernovae. Novae are named according to their constellation together with the year of their occurrance (e.g., "Nova Cygni 1975"), and later given a variable star designation ("Nova Cygni 1975" is also "V 1500 Cygni"). Supernovae are named for their year of occurrance and an uppercase letter, e.g., "SN 1987A". If the alphabet is exhausted, double lower case naming is used: [Year] aa .. az, ba .. bz, etc; e.g., "SN 1997bs".

A summary of guidelines for naming stars and other astronomical objects has been brought out in 1983 by the IAU: First Dictionary of the Nomenclature of Celestial Objects.

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