Alpha Cephei
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| Observation data Equinox J2000 |
|
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 18m 34.8s |
| Declination | +62° 35′ 08.0″ |
| Apparent magnitude (V) | 2.45 |
| Characteristics | |
| Spectral type | A7 IV |
| U-B color index | 0.12 |
| B-V color index | 0.22 |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | -11.5 km/s |
| Proper motion (μ) | RA: 149.91 mas/yr Dec.: 48.27 mas/yr |
| Parallax (π) | 66.84 ± 0.49 mas |
| Distance | 48.8 ± 0.4 ly (15 ± 0.1 pc) |
| Absolute magnitude (MV) | 1.57 |
| Details | |
| Mass | 1.9 M☉ |
| Radius | 2.5 R☉ |
| Luminosity | 18 L☉ |
| Temperature | 7,600 K |
| Metallicity | ? |
| Rotation | 246 km/s. |
| Age | ? years |
| Other designations | |
Alpha Cephei (α Cep / α Cephei) is a star in the constellation of Cepheus. It also has the traditional name Alderamin.
Alderamin is a fairly sun-like star, albeit somewhat hotter and more massive. It appears to be nearing the end of its life as a main sequence star, and may begin fusing helium as it swells into a red giant or perhaps a subgiant. Alderamin is noted for having an unusually fast rotation, although the effects of this rotation are not well understood.
The name Alderamin is a contraction of the Arabic phrase الذراع اليمين að-ðirā‘ al-yamīn "the right arm", with the first definite article transliterated literally as al, as is often the case with Arabic star names. It is known as 天鉤五 (the Fifth Star of the Celestial Hook) in Chinese.
This star is located near the precessional path traced across the celestial sphere by the Earth's north pole. That means that periodically this star comes within 3° of being a pole star, much as polaris is at present. This will next occur about the year 7,500 A.D.
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