What is Nebula?
Nebula refers to the region or cloud of space dust and gases, including hydrogen, helium and other ionized gases that appear as a hazy bright or dark patch. It is also called as nebulosity. The word nebula came from the Latin word for cloud.
Nebula represents either the regions of newly forming stars or the remains of the dead or dying stars.
They have different types, sizes and shapes. There are four main types of nebulas;
1. Planetary nebulas:
About 200 years ago, William Herschel referred some form of spherical clouds as the planetary nebulae as they were round like the planets. Planetary nebulae are created when the star explodes its outer layer. These outer layers of gas expand just like the shape of a ring or bubble. At the center of planetary nebulae, remaining form of star could be seen.
2. Reflection nebulas:
Reflection nebula refers to the dust and gas cloud glowing by the reflection of light from the nearby stars. Brightest reflection nebulae refer to the places of new star formation. Sometimes, the thickness of the gas inhibits the visibility of the new stars.
3. Emission nebulas:
These refer to the glowing hot gases and dust clouds in space. These nebulas reach the high temperature after absorbing light from the nearby stars. They are usually present where new stars are forming.
4. Absorption nebulas:
Absorption nebulas or dark nebulas are the dark clouds in space that block the light from the space behind it by absorption. Dark nebulas are difficult to spot but with the brighter region of the space behind it.
Some of the more prominent nebulae are the Carina, Crab, Manatee, Eagle, Orion (showing many newly forming stars), Pelican, Ring, Helix and Rosette Nebula.
Source: Cool Cosmos