Blue Snowball Nebula (NGC 7662 / Caldwell 22)
Coordinates, Gaia DR3 distance (1.76 kpc), magnitude 8.3, vivid O-III/He-II blue-green excitation, and observing guide for NGC 7662 in Andromeda.
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) | 8.3 mag | ± 0.1 mag | Integrated CCD aperture photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 5740 ly | ± 260 ly | Gaia DR3 trigonometric parallax of 13.2-mag central star (1.76 ± 0.08 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent outer crown diameter | 0.55 arcmin | ± 0.05 arcmin | Outer optical shell (32″ × 28″; bright inner ring is 17″ × 12″) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Blue Snowball Nebula (NGC 7662 in Andromeda) at RA 23h 25m 53.95s, Dec +42° 32′ 05.8″ within Andromeda, 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 Blue Snowball Nebula (NGC 7662, Caldwell 22) is one of the brightest and most vibrantly colored planetary nebulae in the northern autumn sky, situated 5,740 light-years (1.76 ± 0.08 kiloparsecs) away in northern Andromeda. Discovered by William Herschel on October 6, 1784, NGC 7662 packs an integrated visual magnitude of 8.3 into a compact 32 × 28 arcsecond oval disk, giving it an extraordinary surface brightness (~14.8 mag/arcsec²) that readily stimulates the human eye's color-sensing cone photoreceptors.
Why does NGC 7662 look decidedly blue-turquoise rather than purely emerald-green like many other planetary nebulae? Its central white-dwarf progenitor is scorching hot—exceeding 100,000 K—which floods the inner cavity with hard ultraviolet photons energetic enough (>54.4 eV) to doubly ionize helium. Strong blue He II (468.6 nm) and H-beta (486.1 nm) emission blend with the teal [O III] doublet (495.9/500.7 nm) to shift the perceived visual hue toward icy blue.
High-resolution Hubble Space Telescope and Chandra X-ray imaging show that NGC 7662 is a triple-shell system consisting of a bright, tilted inner prolate rim (17 × 12 arcseconds) enclosing a hot X-ray wind bubble, surrounded by a softer 32-arcsecond middle crown and faint polar FLIER jets.
Practical Visual Observing Guide
- Easy to star-hop via the 'Fredrick's Glory' asterism (ι, κ, and λ Andromedae): move 2.5° west-southwest from Iota Andromedae to 5th-magnitude 13 Andromedae, then nudge 25′ southwest.
- Even a 60–90 mm refractor at 60×–100× reveals a non-stellar, distinctly blue-tinted orb that looks strikingly like the planet Neptune or Uranus on steroids.
- Because the central star is relatively faint (magnitude 13.2) against the blazing inner ring, use 250×–400× in a 200–300 mm+ telescope to resolve the bright 17″ × 12″ inner C-shaped ring floating inside the softer 32″ outer snowball.
Catalog Cross-Identifications & Aliases
Common Aliases: NGC 7662 · Blue Snowball Nebula · Caldwell 22
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 7662 |
| SIMBAD | NGC 7662 |
| WIKIDATA | Q488502 |
Related Objects, Comparisons & Guides
Cat's Eye Nebula (NGC 6543 in Draco)
Coordinates, Gaia DR3 distance (1.07 kpc), William Huggins 1864 nebulium spectroscopy, and high-power observing guide for NGC 6543 in Draco.
Blinking Planetary (NGC 6826 in Cygnus)
Coordinates, Gaia DR3 distance (1.30 kpc), magnitude 8.8, rod/cone averted-vision blinking illusion, and observing guide for NGC 6826 in Cygnus.
Saturn Nebula (NGC 7009 in Aquarius)
Coordinates, Gaia DR3 distance (1.26 kpc), magnitude 8.0, low-ionization ansae jets, and high-power observing guide for NGC 7009 in Aquarius.
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.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
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