The Trifid Nebula was discovered by Charles Messier in 1764 and was entered into his catalogue as M20. The name Trifid, first used by Sir John Herschel, is derived from Latin and means “split into three parts”. It is an unusual combination of three types of nebulae: the red part is an emission nebula, energised by the bright young stars at its centre, in which ionised hydrogen is emitting light. The blue part is a reflection nebula, where gas and dust more distant from the hot, blue stars, reflect their light. Finally there is a dark nebula, clouds of dust which block the light from the bright nebulae behind them.