The solar system consists of an average star, known as the sun, and nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. It also includes: the satellites of the planets, numerous comets, asteroids, metioroids and the interplanetary medium.

The sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The whole solar system, together with the local stars visible on a clear night, orbits the centre of our home galaxy, a spiral disk of 200 billion starts, which we call the Milkyway.

The Earth orbits the sun with eight other planets, millions of asteroids and perhaps trillions of comets. These objects are held in their orbits by the equilibrium motions of their gravitational attraction towards the sun and a perpendicular velocity away from the sun.

While the planets may appear to move through the night sky just as stars do, they are also moving in their own orbits around the sun. Repeated observations, infact, show that the planets move with respect to seemingly fixed stars in the distant background.


Except the Uranus and Venus, rest of the planets rotate the west to east direction, however, their period of revolution vary.