RR Lyrae is a type of variable star that is used as a standard candle in astronomy. These stars are typically found in globular clusters and are characterized by their periodic brightness changes, which occur over a few hours. The variations in brightness are due to pulsations in the star's outer layers. RR Lyrae stars are important for measuring distances in the universe. Their consistent pulsation periods allow astronomers to determine their absolute brightness, making it easier to calculate how far away they are. This property helps in understanding the structure and scale of our galaxy, the Milky Way.