Alderamin
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Alderamin
Alderamin (Alpha Cephei, α Cep)
The brightest star in Cepheus and a subgiant A star. Its name comes from the Arabic al dhira al yamin, meaning “right arm,” which apparently refers to the arm of the king whom the constellation represents. Alderamin lies close to the precessional path of the north celestial pole (see precession of equinoxes), so that it periodically comes within 3° of being an exact pole star—a status it last held in about 18,000 B.C. 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 that is common to stars of this class. The rapid spin may also be tied to Alderamin's activity. The Sun is magnetically active because its outer third is subject to large convective currents. Such convective zones aren't generally expected in A-type stars; yet Alderamin emits roughly the same amount of X-ray radiation as does the Sun.
The brightest star in Cepheus and a subgiant A star. Its name comes from the Arabic al dhira al yamin, meaning “right arm,” which apparently refers to the arm of the king whom the constellation represents. Alderamin lies close to the precessional path of the north celestial pole (see precession of equinoxes), so that it periodically comes within 3° of being an exact pole star—a status it last held in about 18,000 B.C. 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 that is common to stars of this class. The rapid spin may also be tied to Alderamin's activity. The Sun is magnetically active because its outer third is subject to large convective currents. Such convective zones aren't 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 (est.): | 2.5 Rsun |
| Mass (est.): | 1.9 Msun |
| Distance: | 49 light-years |
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