Beta Hydri
Beta Hydri (β Hyi, β Hydri) is a star in the southern circumpolar constellation of Hydrus. (Note that Hydrus is not the same as Hydra.) With an apparent visual magnitude of 2.8, this is the brightest star in the constellation. Based upon parallax measurements the distance to this star is about 24.33 light-years (7.46 parsecs).
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydrus |
| Right ascension | 00h 25m 45.07036s |
| Declination | –77° 15′ 15.2860″ |
| Apparent magnitude (V) | 2.80 |
| Characteristics | |
| Spectral type | G2 IV |
| U−B color index | +0.11 |
| B−V color index | +0.62 |
| Astrometry | |
| Radial velocity (Rv) | +22.4 km/s |
| Proper motion (μ) | RA: +2,219.54 mas/yr Dec.: +324.09 mas/yr |
| Parallax (π) | 134.07 ± 0.11 mas |
| Distance | 24.33 ± 0.02 ly (7.459 ± 0.006 pc) |
| Absolute magnitude (MV) | 3.45 ± 0.01 |
| Details | |
| Mass | 1.08 ± 0.03 M☉ |
| Radius | 1.809 ± 0.015 R☉ |
| Luminosity | 3.494 ± 0.087 L☉ |
| Surface gravity (log g) | 4.02 ± 0.04 cgs |
| Temperature | 5,872 ± 44 K |
| Metallicity [Fe/H] | −0.10 ± 0.07 dex |
| Rotational velocity (v sin i) | 6.0 km/s |
| Age | 6.40 ± 0.56 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This star has about 104% of the mass of the Sun and 181% of the Sun's radius, with more than three times the Sun's luminosity. The spectrum of this star matches a stellar classification of G2 IV, with the luminosity class of 'IV' indicating this is a subgiant star. As such, it is a slightly more evolved star than the Sun, with the supply of hydrogen at its core becoming exhausted. It is one of the oldest stars in the solar neighborhood. This star bears some resemblance to what the Sun might look like in the far distant future, making it an object of interest to astronomers.
At a distance of 13°, it is the closest easily visible star to the south celestial pole, and around 150 BC it was within two degrees of it, which made it the southern pole star.