The Greek letters assigned to the stars in a constellation, usually in order of brightness as presented by Johann Bayer in his sky atlas (1603).

Johann Bayer was a German lawyer and uranographer (celestial cartographer or someone who maps stars, galaxies, and other celestial bodies). He is most famous for his star atlas Uranometria, published in 1603, which was the first atlas to cover the entire celestial sphere.

It introduced a new system of star designation which has become known as the "Bayer designation". It introduced twelve new constellations to fill in the far south of the sky, which was unknown to ancient Greece and Rome.