The Bayer designation is the naming system for the brighter stars introduced by Johann Bayer in his star atlas Uranometria (1603), consisting 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 called Alpha, the next brightest Beta, and so on. In practice, there are many cases where the designations are out of order, and there are even cases where a star is named after a different constellation from the one in which it actually lies (according to the modern constellation boundaries). Two stars have double designations – Beta Tauri (Gamma Aurigae) and Alpha Andromedae (Delta Pegasi). Nonetheless, Bayer's system has proved useful and is widely used today.
The designation can be written either in full, as in Alpha Canis Majoris or Beta Persei, or as a lowercase Greek letter before the standard three-letter abbreviation of the constellation. Although most common Bayer letters are Greek, 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. Uppercase Latin Bayer designations never went beyond Q, and names such as W Virginis are variable star 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 binaries), but there are some exceptions such as the chain of stars π1, π2, π3, π4, π5, and π6 Orionis.