The Rosette Nebula (NGC 2237-8, 46) with star cluster (NGC 2244)

Object: NGC 2237-8, 46 (nebula, Caldwell 49), NGC 2244 (open cluster, Caldwell 50)
Type: Emission nebula
Constellation: Monoceras
Distance: 4900 light years

Date: February 23rd, 24th. 2019
Equipment: ATIK 460EX, Vixen 114mm f5.3 ED114 refractor, NEQ6 mount, guiding with Lodestar X2/PHD

Subframes: 36 x 300s H-alpha, 15 x 200s each for RGB (2x2 binned), no flats, hot pixel removal in Astroart (no main frame darks).

The Rosette Nebula (also known as Caldwell 49) is a large H II region located near one end of a giant molecular cloud in the Milky Way galaxy region lying in the constellation of Monoceros.  The nebula has an apparent diameter of over a degree, more than twice the diameter of the full moon.  The open cluster NGC 2244 (Caldwell 50) is embedded within the nebulosity, and is easily seen in a small telescope.  The nebulosity itself is too faint to be seen visually from suburban skies, however.

The constellation of Monoceros is rather dim and ill-defined, lying to the east of its brilliant neighbour Orion.  The location of the Rosette is shown on the Stellarium sky map below:

Interestingly, recent research suggests that the shape of the Rosette nebula is a disc that is (rather fortuitously) orientated face-on to our Earth, rather than a sphere. 

Radiation from the hot young stars of NGC 2244 is sweeping out the gas from the centre of its parent nebula, an effect that can be quite easily seen in the above image.  Researchers at the University of Leeds have found that this cavity is far smaller than it should be given the age and mass of the cluster stars, and have proposed that a combination of magnetic field orientation and a disc-shaped cloud best accounts for the current appearance of the nebula.

The cluster and nebula measure roughly 130 light years in diameter.  The radiation from the cluster stars within the nebula causes the surrounding rarefied gases to fluoresce, producing the visible emission nebula.  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 the Rosette Nebula.  Altogether, approximately 2500 young stars lie in this star-forming complex.  Most of the ongoing star-formation activity is occurring in the dense molecular cloud to the south east of the bubble.

In his excellent book The Caldwell Objects, Steve O’ Meara corrects the still-widespread errors regarding the discovery and cataloguing of the Rosette Nebula. O’Meara credits the discovery of the Rosette’s central cluster, NGC 2244, to William Herschel, who unambiguously recorded the object in 1784.  The surrounding nebulosity was not seen by the eagle-eyed Herschel, but was discovered later in a piecemeal fashion – a testament to the faintness of it.  Albert Marth discovered a part of the bright north-west segment of the nebula (NGC 2238) in 1864, with E.E. Barnard recording a larger part of the same quadrant in 1883 (although Lewis Swift had actually observed it several years earlier).  In 1886, Swift found the bright patch of nebulosity in the eastern quadrant of the Rosette (NGC 2246), but it was not until the early 1890’s that photography showed the full extent of the nebula.

My image clearly shows the dark Bok globules that are strewn across the face of the Rosette.  The “globules” comprise of gas and dust, slowly coalescing from the surrounding nebula under its own forces of gravitational attraction, and are thought to be the birthplace of new stars and planets.

One of these curious areas, which stands out in the northern arch of the Rosette, resembles a leaping cat.  I’m not sure it has a common name or designation, but I have picked it out in the hydrogen alpha image stack, shown above.

I think the whole nebula resembles the skull of a fossilised pre-human, such as pithecanthropus, with the cluster NGC 2244 sitting in its left eye socket.

Colour image processing for the main image was conducted using my usual methods in AstroArt and PaintShop Pro, which are detailed here.

This is a bit of an improvement on my first attempt at imaging this object some 12 years ago.