1. Nebulas are a mixture of the gasses hydrogen and helium, as well as dust and plasma.
2. The beautiful pictures of nebulae that the Hubble telescope beams down are actually three different channels of black and white, which are mixed and painted by scientists to produce the vibrant colors we see in magazines and on television. (The layers are painted according to the composition of the different gasses within the specific nebula.)
3. The word nebula means "cloud" in Latin; indeed, nebulae are space. Variously, the meaning has also been given to mean "mist"; it's fitting, because their varying appearances sometimes do look like a cloud of mist.
4. The galaxy Andromeda was initially believed to be a nebula before Edwin Hubble proved that Andromeda was actually a galaxy all its own in the 1920's. Before then, it was believed that other galaxies were merely nebulas and that the universe only consisted of the Milky Way.
5. If you look closely enough, you can see the Orion Nebula near Orion's belt. It looks like a tiny dot to the naked eye, even though it's sixty light-years across.
6. There are two means by which nebulae generally form. Nebulas are often the result of a giant star or a white dwarf going supernova. The Crab Nebula was formed by a supernova in the year 1054.This event was observed by many cultures during the time; when we look at the Crab Nebula, it's hard to imagine that many people can trace back their ancestry before the time it existed. Nebulae such as the Crab Nebula are proof that our universe is constantly changing.
The other means by which a nebula can form is when the gas and dust in space (known as the interstellar medium) becomes so dense, it starts to be pulled in by gravity.
7. Stars can be born inside nebulas, such as the Crab Pulsar which resides within the Crab Nebula. The Crab Pulsar is an extremely young, spinning star, which emits radio waves. Because of its unique nature, changes in the Crab Nebula can be seen in a matter of days (1). This time scale is relatively short compared to the long life spans and slow growth of most celestial bodies.
8. The Cat's Eye Nebula, recognizable in pictures for its vivid colors and vague resemblance to an eye, is a planetary nebula. Planetary nebulae are emission nebulae and often form in the wake of white dwarfs.