The Sun's corona is the outermost layer of the Sun's atmosphere, extending millions of kilometers into space. It is visible during a total solar eclipse as a halo of plasma surrounding the Sun. The corona is much hotter than the Sun's surface, with temperatures reaching up to 1 million degrees Celsius. The corona is composed mainly of ionized gases, or plasma, and is responsible for the solar wind, a stream of charged particles that flows outward into the solar system. This layer plays a crucial role in space weather, affecting satellites and communication systems on Earth.