Gamma Geminorum
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Gemini |
| Right ascension | 06h 37m 42.71050s |
| Declination | +16° 23′ 57.4095″ |
| Apparent magnitude (V) | 1.915 |
| Characteristics | |
| Spectral type | A1IV + G |
| U−B color index | +0.137 |
| B−V color index | +0.005 |
| Astrometry | |
| Radial velocity (Rv) | −12.5 km/s |
| Proper motion (μ) | RA: +13.81 mas/yr Dec.: −54.96 mas/yr |
| Parallax (π) | 29.84±2.23 mas |
| Distance | 109 ± 8 ly (34 ± 3 pc) |
| Absolute magnitude (MV) | −0.68 |
| Orbit | |
| Period (P) | 4,614.51 days |
| Eccentricity (e) | 0.8933 ± 0.0013 |
| Periastron epoch (T) | 244399.13 ± 0.77 |
| Argument of periastron (ω) (secondary) | 312.60 ± 0.60° |
| Semi-amplitude (K1) (primary) | 11.881 ± 0.068 km/s |
| Details | |
| γ Gem A | |
| Mass | 2.81 M☉ |
| Radius | 5.16±0.77 R☉ |
| Luminosity | 207.3+37.2 −31.5 L☉ |
| Surface gravity (log g) | 3.56±0.08 cgs |
| Temperature | 9,190±130 K |
| Metallicity [Fe/H] | –0.12 dex |
| Rotational velocity (v sin i) | 10.7±0.2 km/s |
| γ Gem B | |
| Mass | 1.07 M☉ |
| Other designations | |
| Alhena, 24 Geminorum, BD+16°1223, FK5 251, GCTP1539.00, HIP 31681, HD 47105, HR 2421, SAO 95912 | |
| Database references | |
| SIMBAD | data |
Gamma Geminorum (γ Geminorum, abbreviated Gamma Gem, γ Gem), formally named Alhena /ælˈhiːnə/, is the third-brightest object in the constellation of Gemini. It has an apparent visual magnitude of 1.9, making it easily visible to the naked eye even in urban regions. Based upon parallax measurements with the Hipparcos satellite, it is located at a distance of roughly 109 light-years (33 parsecs).