Johann Bayer was a German lawyer and uranographer. He was born in Rain, Lower Bavaria, in 1572.

Common names are handy for identifying the brightest stars in the sky, but astronomers needed a system for naming all the stars in the sky, including even the faintest ones.

The Bayer system is the first of two naming systems that incorporate constellation names into the identification of stars. It names the brightest stars by assigning a Greek letter (Alpha, Beta, Gamma, Delta, and so on) in an approximate order of decreasing brightness, along with the Latin possessive name of the constellation in which the star resides.

In this system, Sirius, which is in the constellation Canis Major, is known as Alpha Canis Majoris. Betelgeuse, which resides in the constellation Orion, is known as Alpha Orionis.

The ordering of stars by brightness in the Bayer system is only approximate. As an example, Rigel's name according to the Bayer system is Beta Orionis, suggesting it's the star in Orion just dimmer than Betelgeuse—but it's actually brighter. Brightness fluctuations in Betelgeuse make it brighter than Rigel at times, such as when the system was first introduced in 1603.