Naming the Stars (2) ...

Common names are fine for a few bright stars, but we can see thousands of stars with the naked eye and untold billions with telescopes. Therefore, we need more systematic methods to name all the stars that we see.

The Bayer Naming System
One more systematic method is the Bayer system, which names the brighter stars by assigning a constellation (using the Latin genitive case 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 right figure illustrates the Bayer system for the brighter stars in the constellation Orion. Betelgeuse is called alpha Orionis and Rigel is called beta Orionis in the Bayer system. The table below gives the Greek alphabet, with lower case letters on the left and upper case on the right in each column. Here is a list of Latin genitives for constellation names, complete with pronunciation.

The ordering of stars by brightness in the Bayer system is only approximate. For example, Rigel (beta Orionis) is actually slightly brighter than Betelgeuse (alpha Orionis), and Saiph (kappa Orionis) is the sixth brightest star in Orion even though kappa is the tenth letter of the Greek alphabet.

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 (see the figure below right). Here is a list of seventy of the brighter stars, including common names, Bayer names, positions on the celestial sphere, and spectral class (a measure of surface temperature for the star, as we shall discuss later when we consider the properties of stars).


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. As another example, Rigel is called 19-Orionis and Belelgeuse is called 58-Orionis in the Flamsteed system, indicating that Rigel is located further to the west than Betelgeuse in the constellation.

Special Star Catalogs
There are various special star catalogs in which stars may be given names according to some convention adopted for the catalog. Such specialized catalogs are of importance in astronomical research, but we won't discuss them further in our introductory course. However, we will often come upon names that originate from these catalogs. For example, here is a listing of star names from one such catalog. The following table lists the common, Bayer, and Flamsteed names, and the names from three commonly used catalogs, for the brighter stars in Orion.

Some Names for the Brighter Stars in Orion
Common Name Bayer Name Flamsteed Name Harvard Revised Catalog Henry Draper Catalog Hipparcos Catalog
Alnilam epsilon Orionis 46-Orionis HR 1903 HD 37128 HIP 26311
Alnitak zeta Orionis 50-Orionis HR 1948 HD 37742 HIP 26727
Bellatrix gamma Orionis 24-Orionis HR 1790 HD 35468 HIP 25336
Betelgeuse alpha Orionis 58-Orionis HR 2061 HD 39801 HIP 27989
Mintaka delta Orionis 34-Orionis HR 1852 HD 36486 HIP 25930
Rigel beta Orionis 19-Orionis HR 1713 HD 34085 HIP 24436
Saiph kappa Orionis 53-Orionis HR 2004 HD 38771 HIP 27366