The name is a contraction of the Arabic Yad al-Jauza`, translated as the "armpit of the central one," indicating its position in the constellation of Orion. Because of its rich reddish color the star has frequently been referred to as the "martial one," and in Astrology portends military or civic honors. Because it is the first star of Orion to rise, the title of "roarer" or "announcer" has been assigned to it by ancient writers. Other names are:
| Observation data | |
| Semiregular Variable, type SR c | |
| Right ascension (RA, α) (J2000,00) | 05 h 55 m 10.29 s |
| Declination (Dec, δ) (J2000,00) | +07° 24' 25.3" |
| Distance from Earth | 427 ± 92 LY (131 pc) |
| Visual brightness (V) | +0.45m (+0.3m to +0.6m (+1.3m)) |
| Absolute magnitude | -5.3m to -5.0m |
| Physical characteristics | Mean Diameter (dS = 1,392,000 km) | 385,000,000 km | ~ 276.6 dS 2.57 AU | (452 s.u.) |
| Surface area | |
| Volume | |
| Mass | ~ 40 × 1030 kg |
| Relative mass to the Sun (mS = 1.9891 × 1030 kg) | ~ 20 mS |
| Density | |
| Surface gravity | |
| Spectral type | M1-2 Ia-Iab (Red Super Giant) |
| Surface temperature | 3600 K |
| Age | |
| Color (B-V) | +1.850 (Orange-red) | (1.500) |
| V-I | 2.32 |
| Luminosity (LS = 3.827 × 1026 J s-1) | ~ 10,000 LS |
| Orbital characteristics | |
| Period of rotation | |
| Period | ~ 2070 d to 2355 d |
Betelgeuse is of great interest astronomically. It is also one of the first stars to have its diameter measured with a stellar interferometer. The diameter was found to be variable, ranging from 290,000,000 km to 480,000,000 km. At maximum diameter, the star would extend out beyond the orbit of Mars if put in the Sun's place.
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