stellar nomenclatureAlthough most of the brighter stars have special names, as with Sirius or Aldebaran, the general and most convenient method of naming stars was introduced (1603) by Johann Bayer. In the system of Bayer letters, letters of the Greek alphabet – alpha (α), beta (β), gamma (γ), delta (δ), epsilon (∊), zeta (ζ), eta (η), etc. – are allotted to stars in each constellation, usually in order of brightness. The Greek letter is followed by the genitive of the Latin name of the constellation, as with Alpha Orionis or in abbreviated form α Ori. When the 24 Greek letters have been assigned, small Roman letters – a, b, c, etc. – and then capitals – A, B, C, etc. – are used. The letters R–Z were first used by Friedrich Wilhelm August Argelander (1862) to denote variable stars in a particular constellation, and when those have been assigned the lettering RR–RZ, SS–SZ, etc., up to ZZ is employed. If that proves insufficient AA–AZ, BB–BZ, up to QZ (the 334th variable in the constellation) must be used (omitting Js), followed by V335, etc.
The fainter stars, usually invisible to the naked eye, are designated by their number in a star catalog. The numbers in John Flamsteed's Historia Coelestis Britannica (1725) are often adopted when a star has no Greek letter, as with 28 Tauri (Pleione in the Pleiades), the Flamsteed number generally being followed by the genitive of the constellation name. For stars unlisted in Flamsteed's catalog the number in some other catalog is used, the number being preceded by the abbreviation of the name – BD (Bonner Durchmusterung), HD (Henry Draper Catalog), etc. Flamsteed numbered the stars in a constellation in order of right ascension. Most modern catalogs ignore the constellation name and number purely by right ascension.