3. Galaxy

Galaxies are building blocks of the universe. Galaxy is a vast system of billions of stars, which also contains a large number of gas clouds mainly of hydrogen gas (where stars are born), and dust, isolated in space from similar system.

Classification of galaxies

Galaxies are usually classified on the basis of their shape and are of three types :

1) Spiral

2) Elliptical

3) Irregular

Some of the brightest galaxies are elliptical galaxies but spiral galaxies are usually much bigger than others. We live on the outer edge of a spiral type of galaxy called milky way.