A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars.
Most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria (named after Urania, the Greek Muse of Astronomy, along with Uranus, the Greek god of the sky and heavens). Bayer assigned a lower-case Greek letter, such as alpha (α), beta (β), gamma (γ), etc., to each star he catalogued, combined with the Latin name of the star’s parent constellation in genitive (possessive) form. (See List of constellations for the genitive forms.) For example, Aldebaran is designated α Tauri (pronounced Alpha Tauri), which means "Alpha of the Bull". (The letters of the Greek alphabet were used in antiquity as numerals, so Bayer's scheme might be regarded as a numbering system.)
A single constellation may contain fifty or more stars, but the Greek alphabet has only twenty-four letters; when these ran out, Bayer began using lower-case Latin letters: hence s Carinae (s of the Keel) and d Centauri (d of the Centaur). Within constellations having an extremely large number of stars, Bayer eventually advanced to upper-case Latin letters, as in G Scorpii (G of the Scorpion) and N Velorum (N of the Sails). The last letter used by Bayer was Q.
Is Alpha always the brightest star?
For the most part, Bayer assigned Greek and Latin letters to stars in rough order of apparent brightness, from brightest to dimmest, within a particular constellation. Since in a majority of constellations the brightest star is designated Alpha (α), many people wrongly assume that Bayer meant to put the stars exclusively in order of their brightness, but in his day there was no way to measure stellar brightness precisely. Traditionally, the stars were assigned to one of six magnitude classes, and Bayer's catalog lists all the first-magnitude stars, followed by all the second-magnitude stars, and so on. Within each magnitude class, Bayer made no attempt to arrange stars by relative brightness.
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