Rosette Nebula — 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.
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.
Open cluster NGC 2244 was discovered by Flamsteed about 1690. The nebula, however, was not even seen by William Herschel (who found the cluster); its different parts were discovered only by John Herschel (NGC 2239 = GC 1420 = h 392), Marth (NGC 2238 = GC 5361 = Marth 99), and Swift (NGCs 2237 and 2246)