Over last weekend (3rd October) we had some more fine dry weather and I was able to do some more observation with my Dwarf 3 smartscope. The moon was at last quarter but wouldn't rise till 22:44 BST. Astronomical twilight now ends at 20:36 BST. I decided to have a go at a pairing of objects - the open cluster M52 and the Bubble Nebula (NGC 7625, Caldwell 11) in Cassiopeia. I set the telescope to point midway between them. Unfortunately, due to the way the telescope was pointing at set up, I hit the tracking limits and the observation was cut short early. Here is what I obtained after 73x15s:-
The first frame was taken at 22:00 BST and the last at 22:21. The duo-band filter was employed and the gain was set to 60. Auto parameters were used in Stellar Studio. I have increased the saturation and brightness of the image in Photoshop and binned it x2 (please click on the image to see a full-size view).
The Bubble Nebula can be seen in the upper centre of the image and M52 in the lower centre. Here is a closeup view of the nebula seen at the full resolution of the scope:-
You can see clearly how this nebula gets its name. The shell of illuminated gas and dust really does look like a bubble. People have mistaken this object for a planetary nebula (the shell of gas puffed off by a dying star) but the mechanism by which this cavity has been produced is different. Here there is a massive (45 solar mass) O-type star that is emitting copious amounts of ultraviolet radiation. The star is the brightest object within the spherical bubble in this image. The UV radiation is pushing material away from it (via radiation pressure) and creating a void in the giant molecular cloud in which it sits. I am not clear as to why the star isn't located in the centre of the bubble as I would expect. Note that NGC 7625 actually refers to the whole of the HII region illuminated by this star (and others) and this can be seen to spread over most of this cropped frame.
All text and images © Duncan Hale-Sutton 2026
