Mu Cephei
  | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 43m 30.460s |
| Declination | +58° 46′ 48.17″ |
| Apparent magnitude (V) | 3.43–5.1 |
| Characteristics | |
| Evolutionary stage | Red supergiant or red hypergiant |
| Spectral type | M2-Ia (M2e Ia or M2 Ia+) |
| U−B color index | +2.42 |
| B−V color index | +2.35 |
| Variable type | SRc |
| Astrometry | |
| Radial velocity (Rv) | +20.63 km/s |
| Proper motion (μ) | RA: 3.439 mas/yr Dec.: −4.108 mas/yr |
| Parallax (π) | 0.55±0.20 mas |
| Distance | 1,370+190 −140 ly (421+57 −42 pc) |
| Absolute magnitude (MV) | −7.63±0.30 |
| Details | |
| Mass | 11 M☉ |
| Radius | 762 R☉ |
| Luminosity | 110,000 L☉ |
| Surface gravity (log g) | –0.36 cgs |
| Temperature | 3,800 K |
| Age | 10.0±0.1 Myr |
| Other designations | |
| Garnet Star, Herschel's Garnet Star, Erakis, μ Cep, BD+58°2316, HD 206936, HIP 107259, HR 8316, SAO 33693 | |
| Database references | |
| SIMBAD | data |
Mu Cephei is a red supergiant or hypergiant star in the northern constellation Cepheus. It is officially named the Garnet Star; Mu Cephei is its Bayer designation, which is Latinized from μ Cephei and abbreviated Mu Cep or μ Cep. This star appears garnet red and is located at the edge of the IC 1396 nebula. It is a 4th magnitude star easily visible to the naked eye under good observing conditions. Since 1943, the spectrum of this star has served as a spectral standard by which other stars are classified.
Mu Cephei is more than 100,000 times more luminous than the Sun, and has an absolute visual magnitude of −7.6. It is one of the largest known stars and also one of the most luminous and massive of its kind, with a radius around 760 times that of the Sun (R☉), and were it placed in the Sun's position, it would engulf the orbit of Mars and the asteroid belt.