Alpha Cephei
 Location of α Cephei (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 18m 34.7715s |
| Declination | +62° 35′ 08.061″ |
| Apparent magnitude (V) | 2.5141 |
| Characteristics | |
| Spectral type | A8Vn |
| U−B color index | +0.12 |
| B−V color index | +0.21 |
| Variable type | suspected δ Sct |
| Astrometry | |
| Radial velocity (Rv) | −10 km/s |
| Proper motion (μ) |
RA: +150.55 mas/yr Dec.: 49.09 mas/yr |
| Parallax (π) | 66.50 ± 0.11mas |
| Distance | 49.05 ± 0.08 ly (15.04 ± 0.02 pc) |
| Absolute magnitude (MV) | 1.57 |
| Details | |
| Mass | 1.74 M☉ |
| Radius | 2.3 R☉ |
| Luminosity | 17 L☉ |
| Surface gravity (log g) | 3.99 cgs |
| Temperature | 7,740 ± 170 K |
| Rotational velocity (v sin i) | 246 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), also named Alderamin, is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at only 49 light years.
α Cephei (Latinised to Alpha Cephei) is the star's Bayer designation.
It bore the traditional name Alderamin, a contraction of the Arabic phrase الذراع اليمين al-dhirā‘ al-yamīn, meaning "the right arm". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Alderamin for this star.
With a declination in excess of 62 degrees north, Alderamin is mostly visible to observers in the northern hemisphere, though the star is still visible to latitudes as far south as -27°, albeit just above the horizon. The star is circumpolar throughout all of Europe, northern Asia, Canada, and American cities as far south as San Diego. Since Alderamin has an apparent magnitude of about 2.5, the star is easily observable to the naked eye, even in light-polluted cities.
Alderamin is located near the precessional path traced across the celestial sphere by the Earth's North pole. That means that it periodically comes within 3° of being a pole star, much as Polaris is at present. This will next occur about the year 7500 AD. The north pole of Mars lies halfway between Alderamin and the star Deneb.
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