Stars are celestial bodies that emit light of their own. Our sun is also a star. It is convenient to express distances of stars in light years. Stars appear to move from east to west. The pole star appears to be stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth. Some groups of stars appear to form recognizable groups known as constellation. The Sun is the star nearest to the Earth. It is the source of almost all energy on the Earth. The Sun is the main source of heat and light for all the planets.