Alnilam
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Pronunciation | /ælˈnaɪlæm/ |
| Right ascension | 05h 36m 12.81s |
| Declination | −01° 12′ 06.9″ |
| Apparent magnitude (V) | 1.69 (1.64 – 1.74) |
| Characteristics | |
| Evolutionary stage | Blue supergiant |
| Spectral type | B0 Ia |
| U−B color index | −1.03 |
| B−V color index | −0.18 |
| Variable type | α Cygni |
| Astrometry | |
| Radial velocity (Rv) | 25.9 km/s |
| Proper motion (μ) | RA: 1.49 mas/yr Dec.: −1.06 mas/yr |
| Parallax (π) | 1.65±0.45 mas |
| Distance | 1,250±26 ly (384±8 pc) |
| Absolute magnitude (MV) | −6.89 |
| Details | |
| Mass | 28.4±2.0 M☉ |
| Radius | 33.6±1.8 (equatorial) R☉ 22.3±1.2 (polar) R☉ |
| Luminosity | 271,000±38,000 L☉ |
| Surface gravity (log g) | 3.01±0.10 cgs |
| Temperature | 25,000±1,000 K |
| Rotation | 4.27+1.00 −0.00 days |
| Rotational velocity (v sin i) | 220+40 −100 km/s |
| Age | 4.47 Myr |
| Other designations | |
| Alnilam, TD1 4963, ε Ori, 46 Orionis, Orionis, BD−01°969, FK5 210, HD 37128, HIP 26311, HR 1903, SAO 132346, 參宿二 | |
| Database references | |
| SIMBAD | data |
Alnilam is the central star of Orion's Belt in the equatorial constellation of Orion. It has the Bayer designation ε Orionis, which is Latinised to Epsilon Orionis and abbreviated Epsilon Ori or ε Ori. This is a massive, blue supergiant star some 1,250 light-years distant. It is estimated to be 270,000 times as luminous as the Sun, and 28 times as massive.