In astronomy a nebula is defined as, "A diffuse cloud of particles and gases, mainly hydrogen that is visible either as a hazy patch of light, and either by emission or reflection, or an irregular dark region against a brighter background." That's a pretty good definition but when I see one, I define it as a breathtaking sight of colors and shapes in varying degrees of brilliance. I'm sure you have seen some of the images taken by the Hubble telescope over the years.
Did you know there are different kinds of nebulae? Yes, and some of the prominent ones are:
Stellar Nursery: This is a nebula where star formation is occurring. I like to refer to it as a "star nursery," as some scientists do. These nebulae are often illuminated by ultraviolet light which is emitted from the newborn stars. The Eagle nebula is a good example of a star nursery. But our closest star nursery is located in the constellation Orion, located only 1,350 light years from Earth. Just with the naked eye, (and when conditions are right), you can see a hazy patch by Orion's "sword," which is located just below the three stars in his belt. This is the Orion Nebula. With binoculars or a telescope you can see it even better.
Planetary Nebula: This is formed by a shell of gas which was ejected from certain kinds of intensely hot stars, as red giants or super giants. When these stars explode, only the super hot core remains. The first one, called the "Dumbbell Nebula" was discovered in 1764. These nebulae have nothing to do with planets.
Emission Nebula: This type of nebula glows because it is emitting light energy. The reddish light is created by the hydrogen atoms that are formed when electrons and protons combine. This process is caused when a very hot star stirs up a cloud of hydrogen gas. The "Horsehead Nebula" is in front of an emission nebula which illuminates the outline of the horse head.
Reflection Nebula: Is a type of nebula that glows as the dust in it reflects the light of nearby stars. These nebulae are often bluish in color because blue light is more efficiently reflected than red light. An example of one surrounds the Pleiades Cluster.
Ring Nebula: Just as the name implies, the Ring Nebula is a massive cloud of dust and gas that is shaped like a ring. There is a good example of one in Lyra, which is 2,000 light years from Earth.
Since there are so many of these scattered throughout the universe I like to visit the Hubble site to look at some of the images in their library. Looking at these is an awe-inspiring moment of how vast the universe really is and how tiny we are.
Please visit Hubble at http://hubblesite.org/gallery/album/nebula/
Have your own awe-inspired moment.
