Lagoon and Trifid nebulae. Optical image of the Lagoon (M8, NGC 6523; lower centre) and Trifid (M20, NGC 6514; upper right) nebulae. These are both in the constellation Sagittarius. These nebulae are huge clouds of gas and dust which glow due to the ionisation of their hydrogen gas by radiation from hot, young stars embedded in them. The Lagoon nebula contains several dark and dense clouds of dust, known as Bok globules. These appear as small black areas silhouetted on the brighter nebula. It is thought that they may eventually coalesce into new stars. Most large nebulae are now thought to be starbirth regions.