Welcome to Astronomy 101. In this series, we explain fundamental concepts and describe intriguing objects in the cosmos. In this episode, I’ll discuss some of the most familiar sights in the heavens — nebulae.
A “nebula,” the Latin word for cloud, is basically a collection of dust and gas in space. Odds are, if you’re looking at some transfixing bit of astrophotography, the subject will either be a galaxy or a nebula. Originally, astronomers thought they were one and the same and thought of objects like the Andromeda Galaxy as a spiral nebula within our galaxy. Once they learned our Milky Way was not the entire universe, however, they began distinguishing between the two.