Bubble Nebula (NGC 7635 / Caldwell 11 / Sharpless 2-162)
Coordinates, Gaia DR3 distance (2.52 kpc), O6.5f star BD+60 2522 off-center wind cavity, and observing guide for NGC 7635 in Cassiopeia.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Integrated visual magnitude (V) | 10 mag | ± 0.3 mag | Integrated nebular photometry (excluding V=8.67 BD+60 2522) | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 8220 ly | ± 290 ly | Gaia DR3 astrometric parallax of driving star BD+60 2522 (2.52 ± 0.09 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent bubble & Sh2-162 diameter | 15 arcmin | ± 1.5 arcmin | Surrounding Sh2-162 H II cloud (15′ × 8′; spherical bubble is 3.5′ × 3.0′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Bubble Nebula (NGC 7635 in Cassiopeia) at RA 23h 20m 48.00s, Dec +61° 12′ 06.0″ within Cassiopeia, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
The Bubble Nebula (NGC 7635, Caldwell 11, embedded within Sharpless 2-162) is a remarkably spherical 3.5-arcminute (~7-light-year) stellar-wind cavity located 8,220 light-years (2.52 ± 0.09 kiloparsecs) away in the Perseus Spiral Arm in western Cassiopeia, just 35 arcminutes southwest of the open cluster Messier 52. William Herschel discovered the bright northern knot of the bubble on November 3, 1787, and the Hubble Space Telescope celebrated its 26th anniversary in April 2016 with a breathtaking mosaic of the entire iridescent soap-bubble shell.
Blowing the bubble is BD+60 2522 (SAO 20575), an 8.67-magnitude O6.5(n)fp massive star of ~44 solar masses whose 1,800–2,500 km/s stellar wind sheds mass a million times faster than the solar wind. Why does BD+60 2522 sit conspicuously off-center in the northeastern quadrant of a nearly circular bubble? Hydrodynamic simulations show that while the hot interior X-ray shock bubble equalizes pressure uniformly in all directions, the northeastern rim is slamming into a cold, dense molecular cloud wall that brakes its expansion, whereas the southwestern hemisphere expands freely into lower-density gas.
Right beside BD+60 2522 inside the northeastern rim, intense ultraviolet radiation illuminates a bright golden knot of dense molecular pillars and cometary globules that are slowly being photoevaporated inside the wind cavity.
Practical Visual Observing Guide
- Located just 35 arcminutes southwest of the open cluster M52 in western Cassiopeia; both fit comfortably in the same 1° low-power eyepiece field.
- In an 80–150 mm telescope, look first for the 8.7-magnitude driving star BD+60 2522 and the bright fan-shaped H II knot clinging immediately to its north and west.
- Tracing the delicate 3.5-arcminute curved northern and southern rim of the Bubble itself requires dark skies, a 200–350 mm+ aperture at 100×–160×, and an O-III or UHC filter.
Catalog Cross-Identifications & Aliases
Common Aliases: NGC 7635 · Bubble Nebula · Caldwell 11 · Sharpless 2-162
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 7635 |
| SIMBAD | NGC 7635 |
| WIKIDATA | Q488501 |
Related Objects, Comparisons & Guides
Messier 52 (NGC 7654 Salt-and-Pepper Cluster)
Coordinates, Gaia DR3 distance (1.49 kpc), magnitude 6.9, heavy differential dust extinction, and observing guide for M52 in Cassiopeia.
Crescent Nebula (NGC 6888 Wolf-Rayet Bubble)
Coordinates, Gaia DR3 distance (1.80 kpc), WR 136 Wolf-Rayet wind collision physics, and O-III filter observing guide for NGC 6888 in Cygnus.
Thor's Helmet (NGC 2359 Wolf-Rayet Bubble)
Coordinates, Gaia DR3 distance (3.67 kpc), WR 7 Wolf-Rayet star HD 56925, winged-helmet shock geometry, and observing guide for NGC 2359.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.
Surface Brightness & Extended Objects Guide
Why surface brightness (mag/arcsec²) governs nebula and galaxy visibility more than integrated magnitude, and how exit pupil controls eyepiece contrast.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg