Sometimes a star will change luminosity not due to an eclipse, but due to some sort of physical characteristic. These are called variable stars or variables . These changes in brightness can range from 1/1000 of a magnitude to 20 magnitudes over a period of a fraction of a second to many years. Over 150,000 variables are known, and many others are suspected to be variables.
There are two major classes of variable stars: Pulsating Variables and Cataclysmic Variables . Pulsating variable stars swell and shrink, which affects the star’s brightness. One important class of pulsating variable stars is the Cepheid Variables .