Bayer designation

Many of the brighter stars are given names which are known as Bayer designations. These designations, which were introduced by Johann Bayer in his star atlas Uranometria in 1603, consist of a Greek letter followed by the genitive of the name of the constellation in which the star lies. In principle, the brightest star of the constellation should be given the designation Alpha, the next brightest Beta, and so on. In practice, there are numerous examples where the designations are out of order, and there are even cases where a star has a designation for a constellation in which it does not lie (according to the modern constellation boundaries). Two stars have double designations, β Tau (γ Aur) and α And (δ Peg). Nonetheless, these designations have proved useful and are widely used today.

There are two common ways in which Bayer designations can be written. The designation can be written out in full, as in Alpha Canis Majoris or Beta Persei, or a lowercase Greek letter can be used together with the standard 3-letter abbreviation of the constellation, as in α CMa or β Per.

Although most common Bayer letters are Greek, it should also be mentioned that the system was extended, first by using lowercase Latin letters, and then by using uppercase Latin letters. Most of these are little used, but there are some exceptions such as h Persei (which is actually a star cluster) and P Cygni. Note that uppercase Latin Bayer designations never went beyond Q, and names such as W Virginis are variable designations, not Bayer designations.

A further complication is the use of numeric superscripts to distinguish between stars with the same Bayer letter. Usually these are double stars (mostly optical doubles rather than true binary stars), but there are some exceptions such as the chain of stars π¹, π², π³, π⁴, π⁵ and π⁶ Orionis.

See also Flamsteed designation and star designations.