The “Trifid”, aka M20 lies in the constellation Sagittarius at a distance of 5,000 light-years and has a diameter of ~40 light-years. The Trifid is an example of three different types of nebulosity. The bright red central portion is an emission nebula consisting mainly of fluorescent hydrogen radiated by the central star cluster. The dense dust clouds which obscure the light of the core are an example of dark nebulae. The bluish dust surrounding the red core reflects surrounding star light and is appropriately known as a reflection nebula.