The solar system is comprised of the sun and other celestial bodies which do not have light of their own. These bodies are gravitationally bound to the sun and revolve in specific orbits around it. As of now, only one solar system is known in the entire universe. Our planet earth is part of this solar system. Astronomers have, however, conjectured that there might be more than a million such solar systems in the vast universe.
A galaxy is a a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction. The galaxy of which we are part is called the Milky Way and it can be seen in the night sky as a hazy band of light. The Milky Way is made up of about 200 to 400 billion stars, and our solar system is located within this system.
The sun, with all its planets, is revolving around the Milky Way Galaxy at an orbital speed of 200 km/s. The Milky Way is so large and spread out that it takes the sun about 200 million years to make a complete revolution around the centre of the galaxy. What is even more astonishing is the fact that there are about 100 billion such galaxies scattered in the vastness of the cosmos, with each galaxy composed of about 100 billion stars.
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