From the June 2009 issue

What determines the particular shape of nebulae like the Dumbbell, Trifid, and Lagoon?

Cristian Lares, Goldsboro, North Carolina
By | Published: June 22, 2009 | Last updated on May 18, 2023
August 2009 Trifid Nebula
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.