NGC 2238: 'The Rosetta Nebula'
Object type: emission nebula and open cluster
Size: ~ 80 x 60'
Visual Brightness: ~ 6.0
Constellation: Monoceros
Distance: ~ 4500 light years
Exposure data
Date: 2007-02-09
Location: Postalm/Austria (1300m)
Telescope: TMB 80/480 (3.1" Apo f=480mm) + 0.8 TV reducer/flattener
Camera: Starlight XPress SXV-H9
Astronomik H-alpha filter (13nm)
Bicolor technique: (courtsey to Steve Cannistra)
Image type: Ha
(Ha,sG,OIII)
Binning: all 1x1
Exposure time: Ha
25x8m
Exposure time: OIII 18x8m
Exposure time total: 5h 36m
Discovered by John Flamsteed about 1690.
The Rosetta Nebula is a vast cloud of dust and gas, extending over an area of more than 1 degree across, or about 5 times the area covered by the full moon. Its parts have been assigned different NGC numbers: 2237, 2238, 2239, and 2246. Within the nebula, open star cluster NGC 2244 is situated, consisted of the young stars which recently formed from the nebula's material, and the brightest of which make the nebula shine by exciting its atoms to emit radiation. Star formation is still in progress in this vast cloud of interstellar matter; a recent finding of a very young star with a Herbig-Haro type jet by astronomers at the NOAO has been announced in Press Release NOAO 04-03 on January 22, 2004.
Although various values for its distance occur in the literature, our adopted distance from the Sky Catalog 2000 implies a true diameter of the nebula of about 130 light years. Burnham quotes a mass estimation of 10,000 (Minkowski 1949) to 11,000 (Menon 1962) solar masses, so it is one of the more massive diffuse nebulae.
In the hollowed-out centre of the Rosette nebula lies NGC 2244, the cluster of young stars recently formed there. The cluster has itself created the cavity, radiation pressure and stellar winds from the stars blowing the gas and dust away from the young cluster. The hottest (and brightest) members of the group are seen as distinctly blue on this photograph, a colour corresponding to a surface temperature around 20,000K which may be compared with the Sun's 5500K. The nebula and its cluster is at a distance of about 4500 light years and shows many streaks and globules of dust, remnants of the cloud from which the stars form
More information can be found at:
http://www.seds.org/messier/xtra/ngc/n2244.html