The Rosette Nebula (Caldwell 49) is a large spherical H-II region, near the huge molecular cloud in the constellation Unicorn (Monoceros). The cluster and nebula are about 5,000 light years away from Earth and have a diameter of about 130 light years. The mass of the nebula is estimated at about 10,000 solar masses.

In the centre of the Rosette Nebula lies the open cluster NGC 2244 (Caldwell 50), which is formed by the matter of the nebula. Gases are stimulated to glow by the surrounding hot O and B type stars. In the centre of the nebula, NGC 2244 has already cleared a bubble about 12 light years in size due to strong solar winds. Gas clouds still expand by some 20 km/s, so some spectacular star clusters will remain in a few million years.

The Rosette Nebula contains hydrogen and dust, which reflects the light of the very hot stars in NGC 2244, especially in the blue. The pronounced OIII line in the spectrum of the Rosette Nebula is also interesting, which indicates the presence of abundant oxygen.

The Rosette Nebula Complex has the following NGC identifiers

NGC 2237 - part of the nebula region (also used to name the 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 in the nebula (discovered by John Flamsteed 1690)

NGC 2246 - Part of the nebulous region