Some observations require a decent preparation, while other observations come as a pleasant surprise. On a clear night, after I had observed the Belt of Orion with my 8x56 binoculars, I swept the view across the border into the Monoceros region. I wanted to check if the open cluster NGC 2244 was worth a view from my backyard with my binoculars. Last time that I had seen NGC 2244 was with my 100mm refractor. Back then, the eyepiece was equipped with an UHC filter. The Rosette Nebula, NGC 2237, was a faint and difficult target, which vanished when I removed the UHC filter. The sighting with my binoculars could only be inferior to the previous observation. NGC 2244 can be found on a straight line from Betelgeuze to Procyon. I started with Betelgeuze, slewed my view slowly eastward and ran into NGC 2244 within a few seconds. The cluster glowed like a beacon in the dark. As soon as I centred the open cluster in the eyepieces, it lost a bit of its sparkling grandeur. But when I moved the binoculars, NGC 2244 seemed highlighted again in my averted vision. The cause of this effect is the presence of the low surface brightness of the surrounding nebula: the Rosette Nebula! Now Iâ€™m not saying that my binoculars show a detailed object. But they do allow the detection of the presence of this faint nebula, even without any filters. The Rosette Nebula can be named together with the California Nebula, or with NGC 2024. These objects are all difficult to see, but with the right amount of patience, experience and persistence, they are within reach of a pair of binoculars.
The main showpiece is the rectangular shaped open cluster NGC 2244. It is a sparse cluster and counts only one medium star, two faint stars and five very faint stars. The brightest star, 12 Monocerotis, at the SE corner of the cluster is not even a cluster member but a foreground star. NGC 2244 would be a rather boring object if it was not accompanied by the Rosette Nebula, NGC 2237. It takes time and patience to reveal the Rosette in binoculars. A little trick that might help is to keep the field â€˜in motionâ€™. The human retina is more sensitive to moving objects. A slow wobble with the binoculars is sufficient to stimulate the sensitivity of our eyes. The northern region of the Rosette Nebula appears to be the brightest feature of the amorphous glow. The sky E of 12 Mon also shows a brightening. The sky next to the western border of the cluster seems a tad darker, as if there is a hole in the nebula. Keep in mind that these features do not appear immediately. It takes time and patience to reveal these subtle aspects of the Rosette complex.
The Rosette cluster is almost 5000 l-y away and is related to the Monoceros OB2 association. Like the Trapezium stars in the Orion nebula, the cluster members of NGC 2244 are born in the Rosette nebula. They are estimated to be very young: less than 1 million years. Long-exposure pictures show that these young giant stars have blown a hole in the Rosette complex. The Rosette Nebula is huge. It measures over 1Â° in the eyepieces. The Rosette Nebula measures 85 to 100 l-y across, which is 3 to 4 times larger than the Orion Nebula, which is 3 times closer to us. We can only imagine how magnificent the view of the Rosette Nebula would be if it was at the same distance as the Orion Nebula.
The accompanying sketch might not reveal the whole Rosette complex at first sight. I decided to draw the nebula not too bright. You may need to darken the room and to take your time and use averted vision to see the soft tenuous glow of NGC 2237 in the sketch. You can also use the slider at the right side of the windows, and slowly scroll this post. The movement will stimulate the eyes to see subtle brightness variations.
Site : Bekkevoort, Belgium ( 51Â° N )
Date : February 14, 2008
Time : around 21.30UT
Binoculars : Bresser Spezial-Jagd 8x56
Filter : none
Mount : Trico Machine Sky Window
Seeing : 2/5
Transp. : 2.5/5
Sky brightness : 19.60 magnitudes per square arc second near zenith (SQM reading).
Sketch Orientation: N up, W right.
Digital sketch made with Corel Paint Shop Pro X2, based on a raw pencil sketch.
(Note: if the sketch does look too dark on your monitor, try to darken the room.)