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 important for astronomers because they help in understanding stellar evolution and the structure of the universe. There are different types of variable stars, such as Cepheid variables and RR Lyrae stars. These stars have predictable brightness patterns, making them useful as standard candles for measuring distances in space. By studying variable stars, scientists can gain insights into the life cycles of stars and the dynamics of galaxies.