The Monkey Head Nebula (SH2-252 in the Sharpless catalog, NGC 2174) is another, extended emission nebula in the constellation of Orion. In difference to the Orion Nebula or the Horsehead Nebula this region is not located inside the Orion Giant Molecular Cloud A (GMC A) or the Giant Molecular Cloud B (GMC B) but has an approximately five times larger distance from earth. As in the case of the Orion Nebula the intense radiation from a young, massive O-type star (HD 42088) is ionizing the surrounding gas which results in the red color of the cloud. Inside the extended emission region several bright, compact spots (A, B, C, E and F) can be identified. These spots are associated with young B-type like stars which form compact HII regions.

Emission nebula like the Monkey Head Nebula emit most of the visible light in well-defined emission lines. They are therefore ideal targets for Narrow-band observations. In Narrow-band observations special filters are used which only transmit the light of a single spectral line. Pictures made with a Narrow-band filter are black and white pictures. To get a color (RGB) picture, one has to combine three pictures made with different filters. The above color picture was made with three Narrow-band filters for the Halpha (red), OIII (green) and SII (blue) emission lines using a remote telescope (T21) from the iTelescope network in New Mexico/USA.