The stars on the celestial sphere are named in several different ways. As a
result, the brighter stars may have more than one name. We give a brief overview
of naming stars here. A somewhat more extensive discussion may be found in this Sky
and Telescope article.
Common Names
Most of the brighter
stars in the sky have common names that are of historical and mythological
significance. For example, the bright red star in the shoulder region of the
constellation Orion (the Hunter) is called Betelgeuse, which comes from Arabic
and means (roughly) "the armpit of the mighty one" (see adjacent figure). The
brightest star in Orion is a blue-white star called Rigel that is situated at
the opposite corner of the constellation from Betelgeuse (adjacent figure).
As another example, the brightest star in the constellation Cygnus (the Swan) is situated near the aft portion of the beast and is called Deneb, which is also Arabic in origin and means "the tail of the hen".
The Bayer Naming System
Common names are fine
for a few bright stars, but we need a more systematic method to name all the
stars that we see. One more systematic method is the Bayer system, which names
the brighter stars by assigning a constellation (using the Latin possessive of
the name) and a greek letter (Alpha, Beta, Gamma, Delta, Epsilon, . . .) in an
approximate order of decreasing brightness for stars in the constellation. The
adjacent figure illustrates for Orion. Betelgeuse is also called
Alpha-Orionis and Rigel is called Beta Orionis in the Bayer
system.
The ordering of stars by brightness in the classical Bayer system is only approximate. For example, Rigel (Beta Orionis) is actually slightly brighter than Betelgeuse (Alpha Orionis), and Kappa Orionis is considerably brighter than the position of Kappa in the Greek alphabet would suggest.
As a final
example, the brightest star in the nighttime sky is Sirius, which is in the
constellation Canis Major and is termed Alpha Canis Majoris in the
Bayer naming system.
The Flamsteed Naming System
The Bayer system is a little more systematic than a set of common names, but there are only a finite number of letters in the Greek alphabet, so it cannot be used easily to name very many stars. The Flamsteed naming system can in principle be used to name any number of stars. In this system one uses the same Latin possessive of the constellation name as in the Bayer system, but the stars are distinguished, not by their brightness, but by their nearness to the western edge of the constellation by assigning an arabic numeral. Thus, the closest star to the western edge of the constellation Cygnus is called 1-Cygni in the Flamsteed system and 61-Cygni denotes the star that is the 61st closest to the western edge.Star Catalogs
There are various specialized star catalogs in which stars may be given names according to some convention. Such specialized catalogs are of importance in astronomical research, but we won't discuss them further in our introductory course.
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