In the pre-tele­scope era the word Neb­ula was used by observ­ers to describe any “fuzzy” patch present in the night sky that was­n’t sharp like a plan­et or star. The objects presen­ted in this gal­lery are “fuzzy”, but nerver­the­less of dif­fer­ent nature.

Emis­sion Neb­u­lae are also known as HII regions and rep­res­ent bright clouds of fluor­es­cing hydro­gen gas enger­gized by very hot young stars. They mostly shine in a red col­or, the char­ac­ter­ist­ic emis­sion line of hydro­gen. A very nice example is the Rosette Neb­ula (NGC 2244).

Reflec­tion Neb­u­lae refer to clouds of dust with embeded stars which reflect their light. The Great Ori­on Neb­ula (M42) is a clas­sic­al example of this kind of nebula.

Plan­et­ary Neb­u­lae rep­res­ent the last phase of a stars life. When nuc­le­ar power ceases to with­stand the gravi­tity of a sun­like star, it will blow a part of its mater­i­al into space. A typ­ic­al example of this fla­vor of neb­u­lae is the fam­ous Ring Neb­ula (M57) in Lyra.

[descrip­tion from Robert Gend­ler­’s primer]