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: An expansive emission nebulosity lying between Deneb (α-Cyg) and Sadr (γ-Cyg) hosts the three bright reflection nebulae comprised of NGC 6914, the reflection nebula at the center of the image below, NGC 6914a to the immediate south and 6914b to the immediate north. Also known as vdB 131 (NGC 6914a) and vdB 132 (NGC 6914b), these reflection nebula represent collections of newly formed hot stars which light-up the dust in their immediate environment, thus leading to the characteristic (blue) reflection nebulosity. The glowing ionized hydrogen gas in the general area and which also surrounds these young stars (Cygnus OB association) is the building material which leads to their formation. Also visible in the image below are large areas of "dark" nebulosity and where interstellar dust obstructs the light from passing through. This nebulosity lies about 6000 light-years away and spans approximately 100 light-years across.