A variable star is a type of star whose brightness changes over time. This variation can occur for several reasons, including changes in the star's size, temperature, or the presence of nearby objects that block its light. Variable stars are classified into different types based on their behavior, such as Cepheid variables, which have a regular pattern of brightness changes, and RR Lyrae stars, which are older and typically less luminous. Astronomers study variable stars to learn more about the universe, including the distances to galaxies and the properties of stellar evolution. By observing these stars, scientists can gather valuable data that helps improve our understanding of the life cycles of stars and the dynamics of star clusters.