Nebulae. Lagoon Nebula (M8, NGC 6523; centre left) and the Trifid Nebula (M20, NGC 6514; top right). Located some 3500 light years away in the constellation Sagittarius, the nebulae are clouds of interstellar gas and dust. Their red glow comes from hydrogen gas ionised and lit up by hot young stars with the nebulae. The blue part of the Trifid Nebula is a cooler dust cloud which reflects the blue light of hot stars. Several small, round and dark areas are seen within the Lagoon nebula. They are known as Bok globules and are clouds of interstellar dust and gas undergoing a phase of contraction which may lead to the formation of protostars.