Nebulae (plural of Nebula) are one of the most magnificent stellar phenomena to behold. A nebula is a cloud of interstellar gas and dust particles that are illuminated in some manner. The word nebula is derived from Latin and means "cloud".
Some nebulae are believed to be regions of new star formation while others are the remains of dead or dying stars.
Types of Nebula
There are four main types of nebulae:Planetary Nebulae
Planetary nebulae are clouds of dust and gases that surround certain stars. They form during the late stages of the life of some stars. When the star starts to collapse the outer layers of gas are ejected by the star. These layers of gas surround the star and glow with energy from the central star.
Planetary nebulae got their name from early astronomers because they appeared to look like planets when viewed with small telescopes. They are not otherwise related to planets. (Dumbbell Nebula or Ant Nebula)Reflection Nebulae
Reflection nebulae are clouds of dust and gas which are illuminated by the reflected light from nearby stars. The gas atoms in the nebula doesn't give off it's own light, but rather reflects the light from the nearby stars.Emission Nebulae:
Emission nebulae are glowing clouds of interstellar gas and dust which have been excited by some nearby energy source, usually a very hot star. The ultraviolet light from the hot star energizes the gas atoms within the nebula and causes the nebula to emit light.
The Great Nebula in Orion (M42) visible within the Orion constellation is a prime example of an emission nebula. M42 is around 1,600 light-years away from our galaxy and has a diameter of around 20 to 30 light years.Absorption Nebulae
Absorption nebulae are dense clouds which absorb light from behind and thus appear darker than their surroundings. An example of a absorption nebula is the Horsehead Nebula in Orion
- NASA/ NOAO
- Rough Guide to the Universe - John Sealzi (ISBN: 1858289394)