There are a number of stars in the sky. The sun is the most important star for us. There are a large number of smaller heavenly bodies which revolve around the sun. The sun exerts a strong gravitational pull on all these bodies and keeps them rotating in their respective orbits. The planets, their satellites and a large number of other heavenly bodies, kept moving around the sun taken together form the solar system. Planets, satellites (moons), asteroids, comets and meteors are the constituents of the solar system. The sun is at the centre of the solar system.