Pulsating variable stars are a type of star that changes brightness over time due to periodic expansions and contractions. This behavior is caused by internal processes, such as changes in temperature and pressure, which affect the star's outer layers. Common examples include Cepheid variables and RR Lyrae stars, which are used in astronomy to measure distances in the universe. These stars typically have a regular cycle, with some pulsating every few hours while others may take days or weeks. The study of pulsating variable stars helps astronomers understand stellar evolution and the physical properties of stars, contributing to our knowledge of the cosmos.