Emission and Reflection Nebulae

An emission nebula is a glowing cloud of interstellar gas. The gas is emitting light of its own accord cause by some stimulus such as a nearby star exciting the gas. A reflection nebula is a cloud of dust and gas that reflects the light of nearby stars.

The Crescent Nebula - NGC 6888

M20, The Trifid Nebula

Bubble Nebula

M17 - Swan Nebula