For thousands of years, human beings have used the night sky to navigate, keep track of the seasons, and inspire myths and legends. The tradition of naming stars is as old as history itself. Before modern times, however, humans could only name the stars that were visible in the night sky--a tiny fraction of the number of stars we can see today with powerful telescopes. Some stars have beautiful and evocative names, while some stars are designated by unimaginative-sounding groups of numbers and letters. So how do stars get their names?
Today, most stars are not given proper names. However, a few stars have kept names given many years ago. Here are a few ways a star may have come by its name.
Tradition. Some stars stand out from the rest. These "stars among stars" have been singled out with traditional names for centuries. Polaris, for example, is the one star that seems to occupy a fixed position in the heavens. People have been using it as a navigation aid for millennia, and it has had many different names in various cultures. In addition to Polaris, Western culture occasionally refers to it as the North Star or the Pole Star.
Ancient star catalogues. Some star names have been preserved in the works of ancient astronomers. Perhaps the earliest star catalogue we know of was written by Gan De, a Chinese astronomer who lived in the 4th century BC. The Western world's first star catalogue was written by Timocharis, an astronomer from Alexandria, about a hundred years later.
Most of the ancient star names still in use today, however, can be traced to the 2nd century AD. Ptolemy, a Greek mathematician and astronomer who lived in Egypt almost two thousand years ago, wrote a star catalogue in The Almagest, a mathematical and astronomical document outlining star and planetary motions and mechanics.
Ptolemy's catalogue contains over a thousand stars. Most of these are identified first by their position within a certain constellation; second by their longitude and latitude; and third by their magnitude, or brightness. He did give a few stars special names, most of which are in common use today. These include Arcturus, Sirius, Regulus, Capella, and Spica.
Medieval Arabic translations. In the Middle Ages, Ptolemy's Almagest was adopted by Arabic astronomers, who translated many of the original Greek names into Arabic. Most of the Arabic names were derived from Ptolemy's descriptions of the locations of the stars within their constellations. For example, Arab astronomers named a star within the left foot of Orion the Hunter "Rigel," which is Arabic for "foot." Other stars whose names derive from Arabic include Deneb, Betelgeuse, Vega, and Altair.
Prominent astronomers. A very few stars are named after the astronomers who studied them. Barnard's Star, for example, is a red dwarf named after E. E. Barnard, who discovered it in 1916. Van Maanen's Star is the second white dwarf star ever found, and it was named after Adrian Van Maanen, its discoverer. Bessel's Star is named after George Friedrich Bessel, who measured its distance from Earth in 1838.
Powerful people. Even more rarely, a star can be named after an important figure in history. For example, the brightest star in the Canes Venatici (Hunting Dogs) constellation is named Cor Caroli, meaning "Heart of Charles." Historians are not sure whether it was named in honor of King Charles I or King Charles II of England.
Bayer designations. During the early 17th century, German astronomer Johann Bayer traveled by ship to different hemispheres in search of stars to observe. Bayer compiled a star catalogue in which he named stars by designating first a lower-case Greek letter, such as alpha or gamma, and then the Latin name of the constellation each star could be found in. The Latin constellation names were usually given in the possessive form, to indicate the star "belonged" to that constellation. Many of these names are still in use today, including Alpha Centauri, Alpha Canis Majoris, and Beta Persei.
Modern sky catalogues. The situation gets a bit complicated when it comes to the way stars are named today. Astronomers are performing new sky surveys and compiling star catalogues to record new discoveries every day. Some of these catalogues are extremely large--the Guide Star Catalogue II, for example, contains over 998 million stars. There are too many stars to give each one a unique proper name. As a result, most naming conventions depend on a series of numbers indicating the star's location, brightness, and other factors. An example is SDSSp J153259.96-003944.1. The lettered section (SDSSp) indicates that the designation is from the Sloan Digital Sky Survey of preliminary objects, and the numbers give the star's location in the sky.
The stars we see when we look into the sky on a clear night are only a tiny fraction of the number we can see through a powerful telescope--and those in turn represent only a tiny amount of the total number of stars too far away to see. With the billions of stars in existence, it's not practical to give each one a special name of its own. That makes the few stars with proper names almost unique in the universe.