A cataclysmic variable is a binary star system that periodically has a huge explosion at the surface of one of the stars. Most often, the cataclysmic variable consists of a white dwarf and a main sequence star. Matter from the larger, more distended main sequence star flows down toward the surface of the white dwarf. When the accreted material reaches a certain critical mass, it detonates in a powerful thermonuclear explosion. The star is not destroyed, though. After this big flare-up, the cycle of accretion and explosion occurs again, sometimes after a few hours, and sometimes after a few centuries.

One particular kind of cataclysmic variable is called a classical nova. This is not to be confused with a supernova, which is an explosion that obliterates a star. Still, even though classical novae are not quite as titanic, they are very powerful and impressive.