Designations of stars (and other celestial bodies) and their naming is currently primarily mediated in the scientific community by the International Astronomical Union (IAU), a de facto authority. The IAU states that it is keen to make a distinction between the terms name and designation. To the IAU, name refers to the (usually colloquial) term used for a star in everyday speech, while designation is solely alphanumerical and used almost exclusively in official catalogues and for professional astronomy. Many of the names and some of the designations in use today were inherited from the time before the IAU existed. Other designations are being added all the time.
The Bright Star Catalogue, which is a star catalogue listing all stars of apparent magnitude 6.5 or brighter, or roughly every star visible to the naked eye from Earth, contains 9,096 stars. Pre-modern catalogues listed only the brightest of these. Hipparchus in the 2nd century BC enumerated about 850 stars. Johann Bayer in 1603 listed about twice this number. Only a minority of these have proper names; all others are designated by numbers from various catalogues. Only in the 19th century did star catalogues list the naked-eye stars exhaustively. The most voluminous modern catalogues list on the order of a billion stars, out of an estimated total of 200 to 400 billion in the Milky Way.
In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin dated July 2016 included a table of the first two batches of names approved by the WGSN (on 30 June and 20 July 2016) together with names of stars adopted by the IAU Executive Committee Working Group on Public Naming of Planets and Planetary Satellites during the 2015 NameExoWorlds campaign and recognized by the WGSN. Further batches of names were approved on 21 August 2016, 12 September 2016, 5 October 2016 and 6 November 2016. These were listed in a table included in the WGSN's second bulletin dated November 2016. All are included on the current IAU Catalog of Star Names, last updated on 7 November 2016.
- 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 (e.g., Alniyat can refer to Sigma Scorpii or Tau Scorpii, 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 or Flamsteed 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 stars named after people.
Two second-magnitude stars, Alpha Pavonis and Epsilon Carinae, were assigned the proper names Peacock and Avior respectively in 1937 by Her Majesty's Nautical Almanac Office during the creation of The Air Almanac, a navigational almanac for the Royal Air Force. Of the fifty-seven stars included in the new almanac, these two had no classical names. The RAF insisted that all of the stars must have names, so new names were invented for them. These names have been approved by the IAU WGSN.
- It lists many Assyrian/Babylonian and Sumerian star names recovered by archaeology, and some of these (e.g. Sargas and Nunki) have come into general use.
- It lists many Chinese star names (e.g. Cih alias Tsih), though these have not come into general usage.
- Allen represented the "kh" sound by 'h' with a dot above (ḣ) and at least one astronomy book (by Patrick Moore), using Allen as a source, has misread this unfamiliar letter as 'li'.
A few stars are named for individuals. These are mostly names in common use that were taken up by the scientific community at some juncture. The first such case (discounting characters from mythology) was Cor Caroli (α CVn), named in the 17th century for Charles I of England. The remaining examples are mostly named after astronomers, the best known are probably Kapteyn's Star and recently Tabby's Star.
In the absence of any better means of designating a star, catalogue numbers are generally used. Many star catalogues are used for this purpose; see star catalogues.
The first modern schemes for designating stars systematically labelled them within their constellation.
- The Bayer designation is such a system, published by Johann Bayer in 1603. It introduced a system of designating the brightest stars in each constellation by means of Greek (or less often Latin) letters, and is still widely used. Bayer generally assigned letters by magnitude class: 1st magnitude stars received the earliest letters in the alphabet, followed by 2nd magnitude stars, and so forth (though there are many exceptions). The original list of Bayer designations contained 1,564 naked-eye stars, and several stars not catalogued by Bayer have been added by subsequent astronomers.
- The Flamsteed designation also lists stars by constellation, but by number rather than letter, ordering them by increasing right ascension rather than by decreasing brightness. These numbers were assigned not by Flamsteed himself but by the French astronomer J. J. Lalande in a French edition of Flamsteed's catalogue published in 1783.
- The Gould designation for stars visible from the southern hemisphere, introduced by Benjamin Gould (1879), also lists stars by constellation, numbered by increasing right ascension.
- Hevelius and Bode both numbered stars within constellations similarly. Their number systems have fallen out of use, but their designations even now are occasionally mistakenly treated as Flamsteed designations. 47 Tucanae, a number assigned by Bode, is a famous example.
Full-sky star catalogues detach the star designation from the star's constellation and aim at enumerating all stars with apparent magnitude greater than a given cut-off value.
- The Histoire Céleste Française (1801) enumerated 47,390 stars to magnitude 9.
- The Bonner Durchmusterung (1859) was the most complete star catalogue compiled without the aid of photography. It listed a total of 320,000 northern stars, expanded by the Cordoba Durchmusterung (1892) and the Cape Photographic Durchmusterung (1896).
- The Henry Draper Catalogue (1924) listed 225,300 stars to magnitude 10, extended to a total of 359,083 in 1949. The HD numbers remain in widespread use for stars that do not have a Flamsteed or Bayer designation.
- The Bright Star Catalogue of 1930 listed all stars brighter than magnitude 6. It was supplemented to include stars down to magnitude 7.1 in 1983.
- The Catalogue astrographique was compiled between 1891 and 1950 with the aim of listing all stars to magnitude 11, resulting in a list of 4.6 million stars. It is under continued development, now under custody of the U.S. Naval Observatory.
- The USNO-B1.0 catalogue contains over a billion objects, and is also under continued development at the U.S. Naval Observatory.
- The online Guide Star Catalog II (2008) contains 945 million stars to magnitude 21.
Variable stars that do not have Bayer designations are assigned designations in a variable star scheme that superficially extends the Bayer scheme with capital Latin letters in front of the constellation name, starting with letters R to Z. Such designations mark them as variable stars, examples are R Mira, RR Lyrae, etc. (Many variable stars also have designations in other catalogues.)
When a planet is detected around a star, the star is often given a name and number based on the name of the telescope or survey mission that discovered it and based on how many planets have already been discovered by that mission e.g. HAT-P-9, WASP-1, COROT-1, Kepler-4.
Sale of star names by non-scientific entities
Star naming rights are not available for sale via the IAU. Rather, star names are selected on a non-commercial basis by a small number of international organizations of astronomers, scientists, and registration bodies, who assign names consisting usually of a Greek letter followed by the star's constellation name, or less frequently based on their ancient traditional name.
However, there are a number of non-scientific "star-naming" companies that offer to assign personalized names to stars within their own private catalogs. These names are used only within that company (and usually available for viewing on their web site), and are not recognized by the astronomical community, or by competing star-naming companies. A survey conducted by amateur astronomers discovered that 54% of consumers would still want to "name a star" with a non-scientific star-naming company even though they have been warned or informed such naming is not recognized by the astronomical community.
- "Contests to name moons and exoplanets irk International Astronomical Union". Phys.Org. Retrieved 26 November 2016.
- "Now, people can name newly discovered planets, stars and other celestial bodies". The Economic Times. Retrieved 26 November 2016.
- "Naming Stars". IAU. Retrieved 26 November 2016.
- The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version)
- "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- "Final Results of NameExoWorlds Public Vote Released" (Press release). IAU.org. 15 December 2015.
- "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 24 November 2016.
- "IAU Catalog of Star Names". Retrieved 24 November 2016.
- NASA in 1971 compiled a "technical memorandum" collecting a total of 537 named stars. Rhoads, J. W.,Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars, NASA-CR-124573 (1971).
- Sadler, Donald H. (2008). "A Personal History of H.M. Nautical Almanac Office" (PDF). United Kingdom Hydrographic Office. Retrieved 2010-09-26.
- Richard Hinckley Allen (1963-06-01). Star Names: Their Lore and Meaning. Dover Publications. ISBN 978-0486210797.
- "Bayer's Uranometria and Bayer letters". Ian Ridpath. Retrieved 2016-11-12.
- "Flamsteed numbers – where they really came from". Ian Ridpath. Retrieved 2016-11-12.
- Naming of Astronomical Objects
- Andersen, Johannes. "Buying Stars and Star Names". International Astronomical Union. Retrieved 2013-06-04.
- Haselden, Derek. "Naming and Buying Stars: What you should know". Solent Amateur Astronomers. Retrieved 2016-08-10.
- List of popular star names
- The Naming of Stars from the National Maritime Museum
- The Straight Dope: Can you pay $35 to get a star named after you?
- Naming Stars
- Star Properties documentation