There are over 200 stars with proper names, most of which are of Roman, Greek or Arabic origin. However, only a couple of dozen or so of these names are used regularly, examples of which include Arcturus in Boötes, Algenib in Perseus and Betelgeuse in Orion.
A system whereby Greek letters were assigned to stars was introduced by the German astronomer and celestial cartographer Johann Bayer (1572 – 1625) in his star atlas Uranometria, published in 1603. Bayer’s system is applied to the brighter stars within any particular constellation, which are given a letter from the Greek alphabet, followed by the genitive case of the constellation in which the star is located. This genitive case is simply the Latin form meaning ‘of’ the constellation. Examples are the stars Alpha Boötis and Beta Centauri which translate literally as ‘Alpha of Boötes’ and ‘Beta of the Centaur’.
As a general rule, the brightest star in a constellation is labelled Alpha, the second brightest Beta, the third brightest Gamma and so on, although there are some constellations where the system falls down. An example is Gemini where the principal star (Pollux) is designated Beta Geminorum, the second brightest (Castor) being known as Alpha Geminorum.
There are only 24 letters in the Greek alphabet, the consequence of which was that the fainter naked eye stars needed an alternative system of classification. The system in popular use is that devised by the English Astronomer Royal John Flamsteed (1646 – 1719) (right) in which the stars in each constellation are listed numerically in order from west to east. Although many of the brighter stars within any particular constellation will have both Greek letters and Flamsteed numbers, the latter are generally used only when a star does not have a Greek letter.