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Cepheid L Carinae

A variable star is a star that is sometimes brighter or dimmer. Most stars have only very small differences in brightness, like the Sun. But some stars can vary hugely.

There are generally two types of variable stars:

• A star being eclipsed, where the changes in brightness are from perspective, are called extrinsic variables. For example, in a solar eclipse the moon gets between the sun and Earth. Binary star systems sometimes show eclipses, as do planetary systems with giant planets.
• Stars whose brightness actually changes are called intrinsic variables. The stars get bigger and smaller over time. Some pulsate at a constant rate, some do not. All of them change the rate at which energy is put out, which changes their appearance to us.