Nebulae represent clouds of gas and dust which appear as hazy or fuzzy objects when viewed through a telescope and are characterized as one of four types (emission, planetary, reflection or dark). Emission nebulae, such as the Lagoon nebula (M8), simply glow, for example, with a stunning shade of red. Planetary nebulae appear as small greenish disks through a telescope, thus emulating the planets Uranus and Neptune, as a result of gas masses being thrown off by dying stars (ex. M27, Dumbbell nebula) or represent supernova remnants (ex. M1, Crab nebula). In contrast, reflection nebulae are characterized with gas surrounding young stars which reflect the stellar light (ex. M45, Pleiades) and, thus, yield beautiful images of nebulosity. Finally, dark nebulae are detectable and studied only using parts other than the visible spectrum and are believed to be associated with the formation of stars (ex. M16 in Serpens).

Note: The Iris Nebula in Cepheus is one of the most dramatic and brightest examples of a reflection nebula. Lying at a distance of 1400 light-years away and spanning six light-years in diameter, the central star at the middle of the nebula in the image below, HIP 103763 (mag 7.34), has its light reflected by interstellar dust particles in the immediate vicinity, thus leading to the creation of the dramatic wisps of predominantly blue nebulosity (the dust particles inevitably may have led to the same star's formation). As indicated by the image below, an open star cluster lies to the immediate west of the nebula and, as a result, this area is also listed in star cluster catalogs. Discovered by Herschel in 1794, the Iris Nebula lies a few degrees to the east of Alfirk (β-Cep, mag 3.19) and is ideally placed during summer where it is furthest north of the pole star around midnight.