A stellar atmosphere is the outer layer of a star, where gases and plasma exist. This region plays a crucial role in the star's appearance and behavior, influencing its brightness and temperature. The atmosphere is composed mainly of hydrogen and helium, along with trace amounts of other elements. The study of stellar atmospheres helps astronomers understand the processes occurring within stars, including nuclear fusion and stellar evolution. By analyzing light emitted from these atmospheres, scientists can determine a star's composition, age, and distance from Earth, contributing to our knowledge of the universe.