Binary Stars
In this next section, you'll be investigating binary star systems. It had been thought, for a long time, that binary and multiple stars accounted for more than half the stars in our galaxy, but that view may be changing. Our Sun is a solitary star, as far as we know. We have discovered all sorts of combinations of spectral types in binary systems. These are just a few types of binary star systems, however, which we will study.
Visual binaries: In this type the two stars as seen as separate points of light. The orbital period of the stars is generally very long, and the observer must be very patient, for several decades of observations are generally required. Since the discovery of binary stars by William Herschel over two hundred years ago, the orbits of hundreds of these systems have been catloged. One of the most famous visual binaries are the two stars Alcor and Mizar in the handle of the Big Dipper. Another star system that was discovered early in the twentieth century is Sirius.
Eclipsing Binaries: in this second type, the presence of two stars is indicated by periodic eclipses. Eclipsing binaries are one type of variable star. Algol is a prime example of a classical eclipsing binary. Algol was the first star recognized to be an eclipsing binary by John Goodricke back in 1782, and is a very easy star to find for the rest of us. Sky & telescope magazine provides a list of the times of minimum light for Algol.
The lab on eclipsing binaries will use this site to simulate your binary systems for you to analyze. This site has a program that you can download to also create different eclipsing binary systems .
Here is a nice page about the mythology of Algol, which is unfortunately ruined with a lot of nonsense about astrology.
Spectroscopic Binaries: In this type of binary system, only one point of light is seen in a telescope. However, the spectra of two different stars show periodic Doppler shifts, indicating orbital motion. See it here.
Astrometric Binaries: This final type shows only one star. However, that single star shows either visual or spectroscopic proof of orbital motion, usually due to a faint, unseen companion. As with other binary star systems, astrometric binaries can be used to determine the stars' mass.
Look here for a veritable gold mine of resources for binary stars.
What You Need to Know About Binary Stars
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Updated March 7, 2011