| NGC 7635 | |
| Type: | H II REGION |
| Epoch: | J2000 |
| Dist Ly: | 7100 to 11000 |
| Dist Pc: | 3,400 |
| Appmag V: | ~10[1] |
| Size V: | 15 × 8 |
| Radius Ly: | 3 to 5 |
| Constellation: | Cassiopeia |
| Notes: | Shell around SAO 20575 |
| Names: | Bubble Nebula Sharpless 162 (Sh2-162) Caldwell 11 |
NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region 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 magnitude young central star, SAO 20575 (BD+60°2522). 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. It was discovered in November 1787 by William Herschel.[1] The star BD+60°2522 is thought to have a mass of about .
With an 8or telescope, the nebula is visible as an extremely faint and large shell around the star. The nearby 7th magnitude star on the west hinders observation, but one can view the nebula using averted vision. Using a 16to scope, one can see that the faint nebula is irregular, being elongated in the north south direction.