The Rosette Nebula is a large, circular emission nebula in the constellation Monoceros. It surrounds a cluster of hot, young stars known as the Rosette Cluster (NGC 2244). The brightest parts of the nebula have their own NGC catalog numbers.
Discovery and History
Open cluster NGC 2244 was discovered by John Flamsteed around 1690, and also found by William Herschel. The nebula, however, was not seen by Herschel; its different parts were discovered by his son, John Herschel, Marth, and Swift.
Today, the following NGC numbers are used to describe the various parts of the nebula. But note that their descriptions in the original NGC (in quotes) are quite different:
Amateur Observation
The Rosetta Nebula is a vast cloud of dust and gas extending over 1° across, and covers an area about 5 times that of the full moon. With a total magnitude of 4.8, the star cluster NGC 2244 is visible in binoculars, and seen quite well in small telescopes. The cluster appears about 24' across; the brightest star, at its southeast corner, is 12 Monocerotis.
The nebula itself is more difficult to spot visually, and requires telescope with low magnification at a dark site. Good sky transparency, and a wide-field eyepiece, will show a faint circular glow around 80' x 60' in diameter, with a central "hole" containing NGC 2244.
Once identified, high power may be used to see brightness variations and dark material along the nebula’s edge. Telescopes in the 8 to 12 inch range reveal dark lanes snaking across the faint glow. Two dark globules are easily seen in the western and northern sections of the nebulosity.
The Rosette Nebula is easier to observe photographically; this is the only way to record its red color, which is not seen visually.
Physical Properties
The Rosette is an H II region at a distance of some 5,200 light years, near one end of a large molecular cloud in Monoceros (though distance estimates vary considerably). Its diameter is about 130 light years, and the central hole is about 30 light years across. The nebula is estimated to contain around 10,000 solar masses.
The open cluster NGC 2244 is closely associated with the nebulosity, having recently formed from the nebula itself. Ultraviolet radiation from its hot O-type stars energizes the nebula, causing it to fluoresce. They heat the surrounding gas to a temperature around 6 million K, generating large amounts of X-ray emission seen by the Chandra X-ray Observatory in 2001.
Stellar winds from this group of stars have swept out the hollow at the center of the Rosette. These stellar winds exert pressure on the interstellar cloud, and compress it. This leads to star formation, which is currently still ongoing in this vast cloud of interstellar matter; astronomers announced the finding of a very young star with a Herbig-Haro jet in 2004.