Alderamin (Alpha Cephei)

Alderamin (Alpha Cephei) is the brightest star in the constellation Cepheus and a subgiant A star. Its name, commonly translated from the Arabic al dhira al yamin, meaning "right arm," apparently refers the arm of the king whom the constellation represents.


Alderamin lies close to the precessional path of the north celestial pole, so that it periodically comes within 3° of being an exact pole star – a status it last held in about 18,000 BC and will hold again about 5,500 years from now. Its unusually high rotational speed of 246 km/s at the equator (about 125 times higher than the Sun's), prevents the separation of chemical elements which is common to stars of this class. The rapid spin may also be related to Alderamin's activity. The Sun is magnetically active because its outer third is subject to large convective currents. Such convective zones are not generally expected in A-type stars; yet Alderamin emits roughly the same amount of X-ray radiation as does the Sun.


visual magnitude 2.45
absolute magnitude 1.57
spectral type A7IV
surface temperature 7,600 K
luminosity 18 Lsun
radius ~2.5 Rsun
mass ~1.9 Msun
distance 48.8 light-years (15.0 pc)
position RA 21h 18m 34.8s,
Dec +62° 35' 8"
other designations 5 Cephei, Gl 826, HR 8162,
BD +61°2111, HD 203280,
GCTP 5139.00, SAO 19302,
FK5 803, HIP 105199