Orion the Hunter is one of the best-known constellations in the sky. Just below Orion's belt his sword holds a treasure, the beautiful Orion Nebula. This object, also known as M 42, is a wide complex of gas and dust, illuminated by several massive and hot stars at its core, the Trapezium stars. For astronomers, the Orion Nebula, located some 1,500 light years from Earth, is surely one of the most important objects, as it contains one of the nearest and most active stellar nurseries in the Milky Way, the galaxy in which we live.