Vast amounts of ultra-violet radiation are required to make the gas hot enough to shine. An example of a nebula in which the gas itself glows is M42, The Orion nebula , located in the sword of Orion. This nebula is located 1,500 light years away, along our spiral arm in the Milky Way galaxy. Many faint stars are also present, which have not yet finished gravitationally collapsing,yet still have become hot enough to be self-luminous. The gas in the Orion nebula contains large amounts of ionized hydrogen and oxygen.
Atoms are ordinarily neutral in charge.
When an atom heats up, it begins to lose electronsand becomes positively charged, or ionized. Different atoms lose electrons at different temperatures. The oxygen electrons in the Orion nebula are bound more tightly than the hydrogen electrons. There are four extremely luminous O-type stars which contribute the bulkof the illumination of the Orion nebula. This cluster is known as the Trapezium, because of its trapezoidal shape.