Mirach
Mirach/ˈmaɪræk/, Bayer designation Beta Andromedae, Latinized from β Andromedae, is a prominent star in the northern constellation of Andromeda. It is northeast of the Great Square of Pegasus and is potentially visible to all observers north of latitude 54° S. It is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is seven arcminutes away from Mirach.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 01h 09m 43.91s |
| Declination | +35° 37′ 13.8″ |
| Apparent magnitude (V) | 2.067 (2.01 to 2.10) |
| Characteristics | |
| Evolutionary stage | Asymptotic giant branch |
| Spectral type | M0 III |
| U−B color index | +1.96 |
| B−V color index | +1.57 |
| V−R color index | 0.9 |
| R−I color index | +1.00 |
| Variable type | Semiregular |
| Astrometry | |
| Radial velocity (Rv) | 0.06±0.13 km/s |
| Proper motion (μ) | RA: 175.90 mas/yr Dec.: −112.20 mas/yr |
| Parallax (π) | 16.52 ± 0.56 mas |
| Distance | 199.27±9.27 ly (61.12±2.84 pc) |
| Absolute magnitude (MV) | −1.76 |
| Details | |
| Mass | 2.49 M☉ |
| Radius | 86.4 R☉ |
| Luminosity | 1,675 L☉ |
| Surface gravity (log g) | 0.541 cgs |
| Temperature | 3,802 K |
| Metallicity [Fe/H] | −0.03 dex |
| Rotation | <7900 d (<21.6 years) |
| Rotational velocity (v sin i) | 6 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
This star has an apparent visual magnitude of around 2.07, varying between 2.01 and 2.10, which at times makes it the brightest star in the constellation. Based upon parallax measurements, it is roughly 197 light-years (60 parsecs) from the Sun. Its apparent magnitude is reduced by 0.06 by extinction due to gas and dust along the line of sight. The star has a negligible radial velocity of 0.1 km/s, but with a relatively large proper motion, traversing the celestial sphere at 0.208″·yr−1.