NGC 7635 - Bubble Nebula in Cassiopeia

The Bubble Nebula (NGC 7635) is a peculiar 12th magnitude planetary nebula. The open star cluster M 52 appears nearby.

It was discovered in 1787 by Friedrich Wilhelm Herschel. With an 8 telescope, the nebula is visible as an extremely faint and large shell around the magnitude 8.7 star SAO 20575. The nearby 7th magnitude star on the west hinders observation, but one can view the nebula using averted vision. Using a 16 to 18-inch scope, one can see that the faint nebula is irregular, and elongated in the north-south direction.

NGC 7635 is about 11,000 light years away. The "bubble" in NGC 7635 is about 10 light years across. It was created by a fierce stellar wind from the hot, young, massive central star, which has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The nebula is being energized by the hot central star, causing it to glow. The central star SAO 20575 is thought to have a mass of 10-20 solar masses.