An RR Lyrae star, like a Cepheid variable, also pulsates because of internal processes. It too follows a period-luminosity relation, and can be used as a standard candle. In fact, RR Lyrae stars were used as standard candles before Cepheids; they helped astronomers determine the size of the Milky Way galaxy by measuring the distances to star clusters that orbit the center of our galaxy. RR Lyraes are not as famous as Cepheids as standard candles, mostly because they are somewhat fainter than Cepheids and are not easily usable at very large (intergalactic) distances. Still, they are uniquely valuable because they are much older than Cepheids, so they can be used as distance indicators to objects with older stellar populations.