The Sun is extremely hot and self-luminous body. It is made of hydrogenous matter. It is the star nearest to the Earth. Its mass is about 1.989 x 1080 kg. Its radius is about 6.95 x 108 m. Its distance from the Earth is 1.496 x 1011 m. This is known as astronomical unit (AU). Light of the sun takes 8 minutes 20 seconds to reach the Earth. The gravitational force of attraction on the surface of the Sun is about 28 limes that on the surface of the Earth.
Sun rotates about its axis from East to West. The period of revolution is 34 days at the pole and 25 days at the equator. The density of material is one fourth that of the Earth. The inner part of the Sun is a bright disc of temperature 14 x 106 K known as photosphere. The outer most layer of the Sun of temperature 6000 K is called chromosphere.