Mu Cephei
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 43m 30.460s |
| Declination | +58° 46′ 48.166″ |
| Apparent magnitude (V) | +4.08 (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 | 2,090 – 3,060 ly (641+148 −144–940+140 −40 pc) |
| Absolute magnitude (MV) | –7.63 |
| Details | |
| Mass | 25 M☉ |
| Radius | 972±228 or 1,259 – 1,420 R☉ |
| Luminosity | 269,000+111,000 −40,000 (135,000 – 340,000) L☉ |
| Surface gravity (log g) | –0.36 cgs |
| Temperature | 3,750 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 brighter than the Sun, with an absolute visual magnitude of −7.6. It is one of the largest known stars with a radius around or over 1,000 times that of the Sun (R☉), and were it placed in the Sun's position, it would engulf the orbits of Mars and Jupiter.