Bellatrix (Gamma Orionis)
Coordinates, Hipparcos distance (252 ly), magnitude 1.64, B2 III spectral standard, and observing guide for Bellatrix in Orion.
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 |
|---|---|---|---|---|---|
| Apparent visual magnitude (V) | 1.64 mag | ± 0.02 mag | Johnson UBV photoelectric photometry (0.05-mag slow micro-variability) | definitive | Hipparcos New Reduction Catalog |
| Trigonometric parallax | 12.92 mas | ± 0.52 mas | Hipparcos New Reduction astrometric solution (77.4 ± 3.1 pc) (J2000.0) | definitive | Hipparcos New Reduction Catalog |
| Distance in light-years | 252.4 ly | ± 10.2 ly | Derived from Hipparcos parallax 12.92 ± 0.52 mas | definitive | Hipparcos New Reduction Catalog |
| Photospheric radius | 5.75 R☉ | ± 0.25 R☉ | Narrabri intensity interferometry angular diameter (0.72 ± 0.04 mas) at 77.4 pc | high-confidence | SIMBAD Astronomical Database (CDS) |
| Effective temperature | 21800 K | ± 400 K | UV & optical B2 III standard-star spectrophotometry | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Bellatrix (Gamma Orionis Blue Giant Star) at RA 05h 25m 07.86s, Dec +06° 20′ 58.9″ within Orion, 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
Bellatrix (Gamma Orionis, Latin for 'the Female Warrior' or 'Amazon Star') marks the western (right-hand) shoulder of Orion the Hunter, shining at apparent visual magnitude 1.64 as the third-brightest star in Orion after Rigel and Betelgeuse and the twenty-fifth brightest star in the entire night sky. While most of Orion's bright stars belong to the distant Orion OB1 association (~1,200–1,500 light-years away), Hipparcos parallax measurements (12.92 ± 0.52 mas) prove that Bellatrix is a foreground star lying just 77.4 ± 3.1 parsecs (252 light-years) from Earth—roughly a third the distance of Rigel and less than a fifth the distance of Orion's Belt!
With an effective surface temperature of 21,800 K, a mass of ~7.7 solar masses, and a radius of 5.75 solar radii, Bellatrix radiates roughly 9,210 times the bolometric luminosity of the Sun (mostly in the ultraviolet). Since 1943, its clean spectrum of neutral helium (He I) and ionized silicon lines has served as a primary anchor standard defining the B2 III spectral class in the Morgan–Keenan system.
Estimated to be ~25 million years old, Bellatrix is near the critical mass boundary (~8 solar masses) separating stars that end their lives as massive oxygen-neon-magnesium white dwarfs from those that undergo electron-capture core-collapse supernovae.
Practical Visual Observing Guide
- Located 7.5° west of Betelgeuse across Orion's shoulders, offering an immediate side-by-side color comparison between a 21,800 K icy blue-white B2 giant (Bellatrix) and a 3,600 K deep orange-red M1 supergiant (Betelgeuse).
- Sweep the surrounding 1.5° field with 10×50 binoculars to see a sparse scattering of 6th-to-9th magnitude B- and A-type stars belonging to the foreground Bellatrix (ASCC 18) moving group.
Catalog Cross-Identifications & Aliases
Common Aliases: γ Orionis · Amazon Star · HD 35468 · HIP 25336 · 24 Orionis
| Catalog Authority | Identifier |
|---|---|
| HIP | HIP 25336 |
| HD | HD 35468 |
| SIMBAD | * gam Ori |
| WIKIDATA | Q13041 |
Related Objects, Comparisons & Guides
Betelgeuse (Alpha Orionis Red Supergiant)
Coordinates, competing optical vs radio distances (168 vs 222 pc), radius, Great Dimming physics, and observing guide for Betelgeuse.
Rigel (Beta Orionis Blue Supergiant)
Coordinates, Hipparcos distance (264 pc), luminosity (120,000 L☉), Rigel BC companion, and observing guide for Rigel in Orion.
Mintaka (Delta Orionis Eclipsing Multiple)
Coordinates, distance (~1,200 ly), magnitude 2.23, 5.73-day O-star eclipsing binary, interstellar Ca II discovery, and guide for Mintaka.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
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
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- 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