Variable stars are stars that appear to vary in brightness over time.

Photometry is the measurement of a star’s brightness over time.

Image Credit: STScI, NASA, AURA, Lowcountry Hall of Science and Math, College of Charleston.

For many types of these stars, the variation in brightness regularly repeats and the periods range from a couple of hours to hundreds of days.

Image Credit: Stanlekub

Observations of variable stars are normally presented in the form of a light curve.

Variable stars are vitally important in astronomy for the information they can provide on the properties of stars.

Image Credit: ThomasK Vbg / CC BY-SA 3.0