The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. It radiates this energy mainly as light, ultraviolet, and infrared radiation, providing the energy for life on Earth.
The Inner Solar System consists of the four terrestrial planets—Mercury, Venus, Earth, and Mars—orbiting within the Asteroid Belt, all composed primarily of rock and metal.