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 cluster Messier 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_☉.

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]

• Lists of nebulae