Most stars have constant luminosity and radius on short timescales. However, some stars display periodical changes in luminosity, and these are called variable, or pulsating stars. Periods range from a few hours to a few months, with the more luminous stars taking longer to go through one cycle. This is significant since a measurement of the period can then be used to calculate the absolute magnitude of the star. Comparing this to the apparent magnitude allows the calculation of the distance to the star. This is useful as we can then accurately measure distances to far off galaxies containing these stars. The stars usually used for these types of calculations are called Cepheids. These are particularly bright supergiant stars and can therefore be seen for large distances, acting as ‘standard candles’.
Authors: Carolyn Brinkworth and Claire Thomas
Last updated: July 2001