A binary star is a system where two stars orbit around a common center of mass. These stars can be very close together or far apart, and they can vary in size, brightness, and type. Binary stars are important for astronomers because they help determine the masses of stars, which is crucial for understanding stellar evolution. There are two main types of binary stars: visual binaries, which can be seen separately through telescopes, and spectroscopic binaries, which are identified by analyzing their light spectra. Studying binary stars contributes to our knowledge of the universe, including the life cycles of stars and the formation of planetary systems.