What is a nebula ?
The simplest definition for a nebula is a cloud of gas and dust.
So what do they do and where did they come from ?
Many nebulae form from a collapse of a star (Supernova) which causes all the layers of the star to burst and release gas through space. This becomes a nebula. The ironic thing is that from that gas other stars form. It is kind of the life cycle of the stars.
Types of nebulae
The first and most known kind is an emission nebula. When light passes through the nebula the atoms become excited and go to a higher energy level. When they drop back down the emit light causing the gas to glow. The different colors in the nebula are caused by different kind of gases. The most famous example of an emission nebula is The Great Nebula in Orion (M42).
The second type on our list is reflection nebula. Reflection nebulae are positioned behind a star cluster form our perspective. The nebula reflects the light of the nearby stars and assumes the color of the stars. Unlike emission nebula, reflection nebula don’t emit any light themselves. Most famous example is The Pleiades (M45).
You can see some sort of clouds near the stars these are reflection nebulae.
Emission nebula + Reflection nebula = Diffuse nebula
Occasionally emission nebula are sometimes seen together with a reflection nebula we call those a diffuse nebula. A great example is the Trifid nebula.
Third is dark nebula. You can’t see a dark nebula hence the name but there is a trick. If you place an emission nebula behind it you could see it. Dark nebulae are very dense that they block the light behind them. The most famous example is the horse-head nebula in Orion.It is placed behind an emission nebula called IC-434.
Moving on we’ve got a planetary nebula. I am not going to go into details much but it is formed when a star dies and the outer layers form around the white dwarf in a spherical shape. A great example is M57 in the constellation Lyra.
If you look closely you can see the white dwarf in the middle.
Last but not least is supernova remnants. Which i hope you guessed it is the aftermath of a supernova. Take a look at this supernova remnant known as the Crab nebula (M1) in the constellation of Taurus.