NGC 2174, the Monkey Head Nebula, is a large emission nebula associated with star cluster NGC 2175 in Orion near the border of Gemini. It also contains some small patches of blue reflection nebulosity.

NGC 2174 is 40 arcminutes in diameter, larger than the full Moon, and is bright enough to be seen in binoculars. It is believed to be located 6,400 light-years away from us. It was discovered by Jean Marie Edouard Stephan in 1877.

Ionized hydrogen gas in the nebula glows red, powered by hot ultraviolet radiation from HD 42088, the brightest star in the cluster. NGC 2174 lies two degrees southwest of supernova remnant IC 443, and four degrees due south of open cluster M35.

There is some confusion in the catalog designations for this nebula. The Revised New General Catalogue of Nonstellar Astronomical Objects by Sulentic and Tifft lists NGC 2174 as a diffuse nebula, and NGC 2175 as a cluster with nebulosity. Sky Catalogue 2000.0 by Hirshfeld and Sinnott lists it as NGC 2174-5 and gives a size as 40 x 30 arcminutes with a note that says "contains cluster."

The NGC/IC Project lists NGC 2174 as a small knot of nebulosity inside of the larger NGC 2175. This is probably correct, although many star charts and popular common usage refer to the large nebula as NGC 2174.

The name "Monkey Head" is a popular name and as with other common names has no official or scientific standing.

North is up in this image.

NGC 2174 Catalogs: NGC 2174 Common Name: Monkey Head Nebula Object Type: Emission Nebula Magnitude: 6.8v Size: 40' x 30' Constellation: Orion Image Field Centered At: RA: 06h 09m 43s Dec: +20° 31' 45"