The Rosette Nebula (also known as Caldwell 49) is an H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formedfrom the nebula’s matter.

The complex has the following New General Catalogue (NGC) designations:

• NGC 2237 – Part of the nebulous region (Also used to denote whole nebula)
• NGC 2238 – Part of the nebulous region
• NGC 2239 – Part of the nebulous region (Discovered by John Herschel)
• NGC 2244 – The open cluster within the nebula (Discovered by John Flamsteed in 1690)^{[citation needed]}
• NGC 2246 – Part of the nebulous region

The cluster and nebula lie at a distance of 5,000 light-years from Earth and measure roughly 130 light years in diameter. The radiation from the young stars excites the atoms in the nebula, causing them to emit radiation themselves producing the emission nebula we see. The mass of the nebula is estimated to be around 10,000 solar masses.