Galaxy is coming from Greek word “galaxi” and is a vast collection of billions of stars, dust and hydrogen gas, isolated in space from similar systems. Galaxies are the building blocks of the universe. There are about 100 billion galaxies in the universe, and each galaxy has on an average 100 billion stars. The two important galaxies in the universe are:
- Milky way galaxy
- Andromeda galaxy
Milky Way galaxy comprises of billions of stars, hydrogen gas and dust. It is 100,000 light years in diameter.