Nebulas are magnificently beautiful celestial clouds composed mostly of hydrogen gas and interstellar dust particles. Many nebulas throughout the universe exist in galaxies. There are many types of nebulas; more specifically, four main types. The categories are Planetary, Diffuse, Supernova Remnants and Dark Nebulas. There are also nebulas under the category Herbig-Haro. These types are very bright and small. This effect is due to jets of gas and other particles which are expelled by a star during its stages of formation.
Planetary Nebulas, as their name suggests, resemble planets. In actuality, however, these nebulas are the shells of star material a red giant sheds during its death stages (when it transforms into a white dwarf star). Since these red giants shed layers, or clouds of gas and other material, this goes along with the definition of a nebula. These types of nebulas are very common and it is usually of no surprise when new ones are spotted.