In this second type of binary, 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. Eclipsing binaries are fairly easy to understand. The two stars in these systems need to be rather close to each other in order to block each other’s light. We plot this changing brightness on what is called a light curve. The orbital periods would be on the order of days, if not hours. Because of the periodic eclipses, these binaries appear as variable stars. Some eclipsing binaries have dramatic changes in brightness, whereas some don’t change by more than a hundredth of a magnitude. So much depends on the orbit.Try this simulation. The most famous eclipsing binary is Algol, discovered by John Goodricke two hundred years ago. Here is a video about The Demon Star.You will be doing the lab on eclipsing binary stars, using the simulation found in the link above.
In a spectroscopic binary, the two stars appear as one point of light, but the existance of two stars is revealed by their shifting spectral lines.Spectroscopic binaries will be in very close orbits, more often than not. A spectroscopic binary could also be an eclipsing binary if the two stars just happen to pass in front of each other. Otherwise, the Doppler Effect reveals their orbital motion. You, of course, know about the Doppler Effect. Also, this type of binary will show the spectra of two different stellar spectral types from a single point of light.