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: NGC 6611 is more commonly referred to as the Eagle Nebula and a 1995 photo by the Hubble Space Telescope involving a small region at its core has become one of the most famous and most-recognized results ever produced by the HST. More specifically, the 1995 photo involving "The Pillars of Creation" depicts star formation with rich evidence of many protostars being in the immediate vicinity. This large expanse of H-II emission lies approximately 6500 light-years away in the constellation of Serpens and spans another 75 light-years across. Similar to other emission nebulae, an open cluster is also associated with the Eagle Nebula and which is embedded within the nebulosity while spanning 15 light-years across and with an apparent diameter of 7 arc-minutes. The open cluster within the Eagle Nebula (NGC 6611) was first discovered by Philippe Loys de Cheseaux in 1745 while the nebula (IC 4703) itself by Messier in 1764.