![August 2009 Trifid Nebula](https://www.astronomy.com/wp-content/uploads/sites/2/2023/02/august-2009-trifid-nebula.jpg)
In the Trifid Nebula (M20), three dense dust lanes cut across glowing gas clouds. The combination creates the object’s distinctive appearance.
Jim and Janet Castano/Adam Block/NOAO/AURA/NSF
A nebula is a vast cloud of gas and dust. The physical processes that shape its appearance differ depending on whether it is an emission nebula or a planetary nebula.