More than one nebula are called nebulae. Nebulae are the basic building blocks of the universe. Sometimes the dust and gas in these clouds begins to contract, or squash together. When things such as clouds contract they get hotter. Nebulae A nebula is a huge, diffuse cloud of gas and dust in intergalactic space.
Nebulas exist within other galaxies as well as in our own Milky Way galaxy.
They are classified as planetary nebulas, supernova remnants, and diffuse nebulas, including reflecting, emission, and dark nebulas. Nebulae Nebulae derive their name from from the Greek word for cloud. They are gigantic clouds of dust and gas in the otherwise mostly empty space between the stars. This page was last updated on March 2001.