2.1.2 What is a nebula?
The word nebula (plural, nebulae) comes from the Latin word meaning unclear, or literally ‘mist’. When we look at Orion with binoculars, or even the naked eye, if it is sufficiently dark, we can see that just above the tip of Orion’s sword is a fuzzy patch. This is the Orion Nebula.
Early astronomers described features in the night sky they could not resolve (i.e. could not get clear images of) as nebulae. We now know that the Orion Nebula, also known as M42, is actually a massive cloud of gas and dust. The gas is mainly hydrogen and helium, although there are significant amounts of other gases, including oxygen. The dust is mainly made from silicon and oxygen, similar to the minerals which make up many of the rocks on Earth.