The Lagoon Nebula, Messier 8, is a star forming region and emission nebula located about 5,000 light years away in the constellation Sagittarius, the Archer. It is about 140 by 60 light years in size, enormous considering that Neptune, the furthest planet in our solar system, orbits at only 4 light hours from the Sun.
The Lagoon Nebula is illuminated by ionized hydrogen gas. Ultraviolet radiation emitted by the young star cluster NGC 6530, which lies inside the cloud, causes surrounding gas atoms to lose electrons. These electrons recombine with their nuclei, and emit light in the process. The radiation and stellar winds from such young stars also eat away at the surrounding gas, carving it into the strange shapes we see in the nebula.