The Orion Nebula Click on image for full size (48K GIF) Image courtesy of NASA

Nebulae come in a variety of shapes. But their appearance is usually due to the type of energy source which is lighting them up. There is lot of gas that we can't see in the Galaxy. Something must happen for the nebulae to reveal themselves.

So, what happens to make nebulae glow? It depends on the type of nebulae. Some are involved in the formation of new stars. These are stellar nurseries called HII regions. The young stars found in HII regions are extremely hot and provide a lot of energy for lighting up nebulae. Some nebulae are created by dying stars: supernova remnants and the planetary nebulae surrounding white dwarfs.