|H II region|
The Rosette Nebula (H-Alpha + RGB)
|Observation data: J2000.0 epoch|
|Right ascension||06h 33m 45s|
|Declination||+04° 59′ 54″|
|Distance||5,200 ly (1,600 pc)|
|Apparent magnitude (V)||9.0|
|Notable features||Multipart nebula|
|Designations||SH 2-275, CTB 21,Caldwell 49|
The Rosette Nebula (also known as Caldwell 49) is a large spherical H II region (circular in appearance) 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 formed from the nebula's matter.
The complex has the following NGC designations:
The cluster and nebula lie at a distance of some 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.
A survey of the nebula with the Chandra X-ray Observatory has revealed the presence of numerous new-born stars inside optical Rosette Nebula and studded within a dense molecular cloud. Altogether, approximately 2500 young stars lie in this star-forming complex, including the massive O-type stars HD 46223 and HD 46150, which are primarily responsible for blowing the ionized bubble. Most of the ongoing star-formation activity is occurring in the dense molecular cloud to the south east of the bubble.
A diffuse X-ray glow is also seen between the stars in the bubble, which has been attributed to a super-hot plasma with temperatures ranging from 1 to 10 million K. This is significantly hotter than the 10,000 K plasmas seen in HII regions, and is likely attributed to the shock-heated winds from the massive O-type stars.
On April 16, 2019 the Oklahoma Legislature passed HB1292 making the Rosette Nebula as the official state astronomical object. Oklahoma Governor Kevin Stitt signed it into law April 22, 2019. 
The cluster of stars is visible in binoculars and quite well seen in small telescopes while the nebula itself is more difficult to spot visually and requires a telescope with a low magnification. A dark site is a must to see it. Photographically the Rosette Nebula is easier to record and it is the only way to record the red color which is not seen visually.