Variable stars represent a wide variety of stars that undergo brightness variation over some period of time. You can explore a wide range of variable stars with Wolfram|Alpha. For example, pulsating variable stars, such as Mira variable stars and Cepheid variable stars, actually expand and contract, resulting in a change in luminosity and surface temperature. Investigate eclipsing variable stars, such as Algol, which change in brightness due to one object in the system blocking the light from another object in the system. Some variable stars have nearly random periods; others have regular periods that can be used to derive their luminosity. Some variable stars are cataclysmic in nature, such as classical novae, and may or may not repeat.