|RR Lyrae variable stars
A member of a large class of pulsating stars of type A2-F6 with periods less than 1 day. They are similar to Cepheids, except that their periods are much shorter and are less luminous. RR Lyrae stars belong to Population II and are often found in globular clusters (hence one of their older names cluster variables) or elsewhere in the galactic halo. They are used as distance indicators (standard candle) out to more than 200 kpc.