Variable stars are stars that exhibit changes in brightness over time. These changes can occur for a variety of reasons, including pulsations, eclipses in binary systems, and changes in mass transfer between stars. Studying variable stars can provide valuable information about the physical properties of stars, such as their mass, size, and age. Variable stars are categorized into different classes based on the nature of their variability, such as Cepheid variables, RR Lyrae variables, and eclipsing binaries. Researchers study variable stars to better understand stellar evolution, the structure of galaxies, and the universe as a whole.