The Universe - Nebulae
Nebula (plural nebulae) was the word once used for any fuzzy patch of light in thr night sky. Nowdays, many nebulae are known to be galaxies instead.
Many nebulae are gigantic clouds of gas and space dust.
Glowing nebulae are named because they give off a dim, red light, as the hydrogen gas in them is heated by radiation from nearby stars.
The Great Nebula of Orion is a glowing nebula just visible to the naked eye.
Reflection nebulae have no light of there own. The can only be seen because starlight shines off the dust in them.
Dark nebulae not only have no light of there own, they also soak up all light. They can only be seen as patches of darkness, blocking out light from the stars behind them.
The Horsehead nebula in Orion is the best-known dark nebula. As its name suggests, it is shaped like a horse's head.
Planetary nebulae are thin rings of gas cloud which are thrown out by dying stars. Despite their name, they have nothing to do with planets.
The Ring nebula in Lyra is the best-known of the planetary nebulae.
The Crab nebula is the remains of a supernova that exploded in AD 1054.