NGC 1931, the Fly Nebula (left side) is an emission and reflection nebula, and has been referred to as a miniature version of the Orion Nebula, as it shares some of the same characteristics. There is a smaller version of M42's "Trapezium" in the hot, young star cluster in the centre of the emission nebula. It is about 3 arcmins in size and is 4000 - 7000 light years from Earth.

IC 417, the Spider Nebula (center right) is an emission nebula and star forming region. The nebula contains a young open cluster (Stock 8), and is energized by its hot, massive blue stars which are still embedded in glowing hydrogen gas. The bluish clouds of gas at the top of the image are locations of new star formation.

The nebulosity emits all of its light in isolated emission lines. The most prominent of those is the H line, which was exclusively recorded to obtain the image shown above, displayed here in gray tones. At a wavelength of 656 nm, it is located at the red end of the visual spectral range, and cannot be not very well perceived by the human eye during nighttime.

NGC 1931 - Fly Nebula and IC 417 - Spider Nebula, which this image is part of.