Some stars do not always shine with the same degree of brightness. Stars that vary in the intensity of their brightness are called variable stars.
Some stars do not always shine with the same degree of brightness. Stars that vary in the intensity of their brightness are called variable stars. There are over 20,000 known variables. They do not all vary for the same reason.
Some variable stars are binary variables. They are double stars, stars that are revolving around each other, and can thus alternately eclipse each other. This causes the point of light that is seen as one star to change in brightness.
Other variable stars are single stars called intrinsic variables. They change in brightness for different reasons. They seem to pulsate. Some of them have regular rhythm of variation; some have very irregular rhythms. Some complete their cycles of variable in a few days; other take years to complete a cycle. Betelgeuse is an irregular intrinsic variable.
A certain type of variable star is called a Cepheid variable. The study of the variations of these stars can tell astronomers how far the star is from earth. Delta Cepheus was the first star of this type to be discovered.
Novae and supernovae stars have bursts of brightness and then become faint.