The differences between these various types of nebulae is often as nebulous as the nebulae themselves.

As you visit the various sites, you will find that some contain components of two or three of the following types.

Some of these are most simply grouped under the term "Diffuse Nebulae" which, however, doesn't differentiate between the various ways that different parts of a particular nebula might be accurately described.

Dark Nebulae	© Anglo-Australian Observatory, Photograph by David Malin, text © David Malin.
	Anglo-Australian Observatory Horsehead The Web Nebulae

Emission Nebulae

Eta Carinae - Hubble Anglo-Australian Observatory The Web Nebulae

UPDATED: 04/01/08 (no joke!)