RR Lyrae variable

The RR Lyrae variable stars fall in a particular area on a Hertzsprung–Russell diagram of color versus brightness.

RR Lyrae variables are periodic variable stars, commonly found in globular clusters and other old stellar populations in galaxies. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.