NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an
H II region[1]emission nebula in the constellation
Cassiopeia. It lies close to the
open clusterMessier 52. The "bubble" is created by the
stellar wind from a massive hot, 8.7[1]magnitude young central
star, SAO 20575 (
BD+60°2522).[7] The nebula is near a giant
molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow.[7] It was discovered in November 1787 by
William Herschel.[5] The star BD+60°2522 is thought to have a mass of about 44 M☉.
Amateur observation
NGC 7635 and its environs imaged through an 8-inch amateur telescope
With an 8-or-10-inch (200 or 250 mm) telescope, the nebula is visible as an extremely faint and large shell around the star.[6][1] The nearby 7th magnitude star on the west hinders observation, but one can view the nebula using
averted vision.[6] Using a 16-to-18-inch (410 to 460 mm) scope, one can see that the faint nebula is irregular, being elongated in the north south direction.[6]
