This narrowband image captures a series of deep sky objects in the constellation of Cassiopeia at a declination of +60 degrees.
The largest object in this image is Sh2-157. This bright emission nebula is located 8000 light-years away and is over 200 light-years across. This nebula has been described as a ring nebula surrounding the Wolf-Rayet star WR 157. WR 157 is a member of the Markarian 50 star cluster. Although I can see the emission fronts expanding from the WR 157 source star, the surrounding structures are very complex and it seems a bit simplistic to me to just describe this fascinating object as a ring nebula.
The most striking object in this image is NGC 7635, the Bubble Nebula, which is located about 7,000 light years away. Although it looks small in the image, the bubble diameter is about 7 light years across. A closeup image of the Bubble is shown
here. This object is caused by a stellar wind emitted from the source star (another Wolf-Rayet star). These WR stars expel a significant amount of mass, resulting in the expanding gas bubble which is contained by the molecular cloud which surrounds it.
Several additional deep sky objects, including a star cluster (NGC 7510), a planetary nebula (PLN 110-0.1), a reflection nebula (GN 25.13.3) and 2 emission nebulae (Sh2-157A & Sh2-159) are identified on the annotated image.
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