(See description below)
Nebula NGC 2170
This region in the constellation of Monoceros displays a wonderful mix of nebula types. The bluish areas are reflection nebulas, so-named because they reflect the light of nearby stars. The dust particle size in these areas preferentially reflects blue light, similar to cigarette and other kinds of smoke. The red areas are emission nebulas, and shine by a different mechanism: ultraviolet light from nearby stars excites hydrogen and other gas atoms in the nebula, which then emit light of their own in specific colors. Finally, what looks a bit like black ink spilled across the image constitutes a dark nebula, and is only seen because of the light that it blocks. In other words, the dark nebula is seen in silhouette.