RR Lyrae

RR Lyrae is the prototype star of the RR Lyrae class of pulsating variable stars, which rhythmically brighten and dim over periods typically ranging from a few hours to about a day. These stars serve as crucial 'standard candles' because their intrinsic brightness is related to their pulsation period, allowing astronomers to measure distances to globular clusters and the galactic halo.

RR Lyrae is located in the constellation Lyra, the same constellation that contains the bright star Vega. Its variability was first noted by Williamina Fleming at the Harvard College Observatory around 1901, during systematic surveys of photographic plates.

RR Lyrae stars follow a well-established period-luminosity relationship: by measuring how long it takes a star to complete one pulsation cycle, astronomers can determine its intrinsic brightness. Comparing this to the star's observed apparent brightness from Earth allows them to calculate the distance, a technique especially useful for measuring distances to globular clusters within the Milky Way.

The star RR Lyrae has a pulsation period of approximately 13.5 hours, meaning it completes one cycle of brightening and dimming in just over half a day. Its apparent magnitude varies between roughly 7 and 8, making it too faint to see with the naked eye but readily observable with a small telescope.