Owl Cluster (NGC 457 / Caldwell 13)
Coordinates, Gaia DR3 distance (2.88 kpc), magnitude 6.4, Phi Cassiopeiae supergiant eyes, and observing guide for NGC 457 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) | 6.4 mag | ± 0.1 mag | Integrated CCD aperture photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 9390 ly | ± 230 ly | Gaia DR3 astrometric parallax of ~700 OB members (2.88 ± 0.07 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent diameter | 13 arcmin | ± 1 arcmin | Visual and photographic core extent | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| OB supergiant turnoff age | 0.021 Gyr | ± 0.003 Gyr | Gaia DR3 B-supergiant turnoff & red supergiant isochrone fitting | high-confidence | ESA Gaia Archive — Data Release 3 |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Owl Cluster (NGC 457 / ET Cluster) at RA 01h 19m 35.00s, Dec +58° 17′ 27.0″ 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 Owl Cluster (NGC 457, Caldwell 13—also famously known at star parties as the 'ET Cluster' or 'Kachina Doll Cluster') is one of the most recognizable stick-figure open clusters in the sky, located 9,390 light-years (2.88 ± 0.07 kiloparsecs) away inside the Perseus Spiral Arm in Cassiopeia. Discovered by William Herschel on October 18, 1787, the cluster spans 13 arcminutes (~36 light-years physically) and is only ~21 million years old.
What gives NGC 457 its unmistakable owl or extraterrestrial silhouette is the brilliant pair of 'eyes' on its southeastern edge—5.0-magnitude yellow-white F0 Ia supergiant Phi-1 Cassiopeiae (φ¹ Cas) and 7.0-magnitude blue-white B6 Ib supergiant Phi-2 Cassiopeiae (φ² Cas, HD 7902)—from which two curving wings of 9th-to-11th magnitude B-type stars sweep outward on either side of a stick-like body and two stubby feet.
If Phi-1 Cassiopeiae is a true co-eval member at NGC 457's 9,390-light-year distance, its absolute visual magnitude reaches an extraordinary M_V ≈ −8.8 (roughly 250,000 times the luminosity of the Sun), placing it among the most luminous yellow hypergiants in the Milky Way alongside the 8.6-magnitude M1.5 Iab red supergiant V466 Cassiopeiae (HD 236697) glowing warmly near the owl's western wingpit.
Practical Visual Observing Guide
- Easy to locate just 2.0° south-southwest of Ruchbah (δ Cassiopeiae), the lower-left knee of the Cassiopeia W.
- Visible in 7×50 binoculars as a V-shaped comet tail streaming northwest from naked-eye star Phi Cassiopeiae.
- In any 60–150 mm telescope at 40×–90×, the glaring yellow-and-blue double eyes (φ¹ and φ² Cas), outstretched wings, and ruby-red heart star V466 Cas make it an instant crowd favorite.
Catalog Cross-Identifications & Aliases
Common Aliases: NGC 457 · Owl Cluster · ET Cluster · Dragonfly Cluster · Caldwell 13
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 457 |
| SIMBAD | NGC 457 |
| WIKIDATA | Q671284 |
Related Objects, Comparisons & Guides
Double Cluster (NGC 869 & NGC 884)
Coordinates, Gaia DR3 distance (2.29 kpc), age 14 Myr, supergiant population, and observing guide for NGC 869 and NGC 884 in Perseus.
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.
Jewel Box Cluster (NGC 4755 / Kappa Crucis)
Coordinates, Gaia DR3 distance (1.97 kpc), magnitude 4.2, supergiant color contrast in the Herschel 'A' asterism, and observing guide for NGC 4755.
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.
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.
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