A nebula consists of clouds of interstellar dust particles and gases. These clouds are the birthplace of new stars.
Gravity causes some of the nebular matter to join together in clumps. Heat and energy build up over millions of years until eventually enough of the hydrogen atoms fuse together to make the clump luminous. Once that happens, that part of the nebula has become a star.
There are three major types of nebulae, and a few sub-types:
- Diffuse (the most common type of nebula)
- Emission
- Reflection
- Dark
Planetary
Bright or Supernova remnant