Star designation

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The International Astronomical Union (IAU) is the internationally recognised authority for assigning designations to stars (and other celestial bodies). Many of the star names in use today were inherited from the time before the IAU existed. Other names, mainly for variable stars (including novae and supernovae), are being added all the time. Most stars, however, have no name and are referred to, if at all, by means of catalogue numbers. This article briefly surveys some of the methods used to designate stars.

1 Proper names
2 Bayer letters
3 Flamsteed numbers
4 Variable designations
5 Catalogue numbers
6 Unofficial names
7 Eponyms

[edit] Proper names

Most bright naked eye stars have traditional names, most of which derive from Arabic, but a few from Latin. See List of traditional star names for a list of some of these names.

There are a number of problems with these names however:

Spellings are often not standardized (Almach or Almaach or Almak or Alamak)
Many stars have more than one name of roughly equal popularity (Mirfak or Algenib or Alcheb; Regor or Suhail al Muhlif; Alkaid or Benetnasch; Gemma or Alphecca; Alpheratz and Sirrah)
Because of imprecision in old star catalogs, it may not be clear exactly which star within a constellation a particular name corresponds to (eg, Alniyat, Chara).
Some stars in entirely different constellations may have the same name: Algenib in Perseus and Algenib in Pegasus; Gienah in Cygnus and Gienah in Corvus, Alnair in Grus and Alnair in Centaurus.

In practice, the traditional names are only universally used for the very brightest stars (Sirius, Arcturus, Vega, etc) and for a small number of slightly less bright but "interesting" stars (Algol, Polaris, Mira, etc). For other naked eye stars, the Bayer designation is often preferred.

In addition to the traditional names, a small number of stars that are "interesting" can have modern English names. For instance Barnard's star has the highest known proper motion of any star and is thus notable even though it is far too faint to be seen with the naked eye. See the list of stars named after people.

[edit] Bayer letters

Johann Bayer introduced a system of designating the brightest stars in each constellation by means of Greek (or less often Latin) letters, a system which is still widely used. See Bayer designation for details.

[edit] Flamsteed numbers

John Flamsteed's numbering of stars within constellations have also remained popular, although Bayer's Greek letters are usually preferred when there is a choice. See Flamsteed designation for details.

[edit] Variable designations

Variable stars which do not have Bayer designations are given special designations which mark them out as variable stars. See variable star designation for details.

[edit] Catalogue numbers

In the absence of any better means of designating a star, catalogue numbers are generally used. A great many different star catalogues are used for this purpose, see star catalogues.

[edit] Unofficial names

Note that there are companies that purport to name obscure stars after paying customers, but these names are recognized by nobody except the registering company and the customer, and there is nothing to stop two companies from claiming the same star, or even one company from registering the same star to two customers. See the Buying a Star FAQ or the IAU's discussion for more information.