| Emission nebula | |
|---|---|
| H II region | |
 Wide field image of NGC 7635 as captured by theHubble Space Telescope | |
| Observation data:J2000epoch | |
| Right ascension | 23h 20m 48.3s[1] |
| Declination | +61° 12′ 06″[1] |
| Distance | 7100[2] to 11000[3][4] ly (3,400 pc) |
| Apparent magnitude (V) | ~10[5] |
| Apparent dimensions (V) | 15′ × 8′[6] |
| Constellation | Cassiopeia |
| Physical characteristics | |
| Radius | 3[2] to 5[7][4] ly |
| Notable features | Shell aroundSAO 20575[1] |
| Designations | Bubble Nebula[1] Sharpless 162 (Sh2-162) Caldwell 11 |
| See also:Lists of nebulae | |
NGC 7635, also known as theBubble Nebula,Sharpless 162, orCaldwell 11, is anH II region[1]emission nebula in the constellationCassiopeia. It lies close to theopen clusterMessier 52. The "bubble" is created by thestellar wind from a massive hot, 8.7[1]magnitude young centralstar, SAO 20575 (BD+60°2522).[7] The nebula is near a giantmolecular 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 byWilliam 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 usingaverted 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]
