NGC 7635 - Diffuse Nebula in Cassiopeia

At a distance of 7,100 light-years from Earth, NGC 7635 (the Bubble Nebula) is located in the constellation Cassiopeia and has a diameter of 10 light-years. This spectacular diffuse nebula can be found about six degrees west-northwest of 2nd-magnitude Beta Cassiopeiae, and just 35 arcminutes southwest of the beautiful open star cluster M52. If you watch carefully, a wealth of detail can be seen in this shell of glowing gas, especially through large apertures. A 6-inch telescope will reveal the nebula as a bright, uniform disk two arcminutes across, surrounding a 9th- magnitude star.

Diffuse nebula NGC 7635. Doug Williams, NOAO/AURA/NSF [larger image]

However, if you use a large telescope, NGC 7635 becomes even more spectacular. Using averted vision, a fainter glow surrounding the central region becomes visible. This feature appears extended east - west and has a somewhat brighter western edge.

Finder map - field width 15 degrees, stars to magnitude 9.5.

• Averted vision - A technique used by amateur astronomers when they observe faint objects. Consists of looking at the object "out of the corner of the eye" - with peripheral vision - in order to detect it more easily. This works because the most optically sensitive part of the retina is off-center.