The ancients believed that the sky was perfectly constant, reflecting a notion god-like perpetuity. The discovery of variable stars put to rest forever the idea of eternally unchanging heavens.
Variable stars fall into four major physical classifications.
These are stars that exhibit varying brightness due to periodic changes in their internal structure. Novae are now understood to be members of binary systems that become unstable due to transfer of matter from one star to the other. Supernovae are the explosive results of instabilities in super-giant stars. We observe these eclipses as a variety of possible light curves that can tell us alot about the sizes and other properties of the two stars. The observation of variable stars is one of the last areas where the amateur can contribute observations with real scientific value.