The Sun is a star at the center of our solar system that is the primary source of energy for life on Earth: Composition The Sun is made of plasma, a state of matter that is similar to gas but with most of the particles ionized. The Sun is mostly made of hydrogen and helium. Size The Sun is about 100 times wider than Earth and 10 times wider than Jupiter. It has a radius of about 700,000 kilometers (432,000 miles). Mass The Sun is more than 333,000 times more massive than Earth and contains about 99.8% of the mass in the solar system. Energy The Sun's core is heated by nuclear fusion reactions, which produce energy that radiates from the Sun's surface as visible light, infrared radiation, and ultraviolet energies. Gravity The Sun's gravity holds the solar system together, keeping everything in its orbit. Rotation The Sun rotates at different speeds in different parts. At its equator, the Sun rotates once in 25 Earth days, while at its poles it rotates once every 36 Earth days. Surface The part of the Sun that we see from Earth is called the photosphere. The Sun doesn't actually have a solid surface because it's a ball of plasma. Future The Sun has enough nuclear fuel to stay as it is now for another 5 billion years. After that, it will swell to become a red giant, then shed its outer layers, and eventually collapse to become a white dwarf.