Alderamin (Alpha Cephei / α Cep / 5 Cep) is a star located in the constellation of Cepheus, the brightest of it with apparent magnitude +2.43. Its name comes from the contraction of the Arabic phrase الذراع اليمن að-ðirā 'al-yaman, whose translation is "the right arm".
At 49 light years away from the Solar System, Alderamin is a white subgiant of spectral type A7IV with an effective temperature of 7600 K. Its luminosity is 20 times greater than that of the Sun and its radius is 2.5 times the radius solar. Like other similar stars, it is slightly variable with an oscillation in its brightness of 0.06 magnitudes; it is cataloged as a Delta Scuti variable. Its rotation speed is very high, at least 246 km / s, completing a turn in less than half a day; this rapid rotation apparently would inhibit the differentiation of chemical elements usually observed in stars of this type. It emits a quantity of X radiation similar to that of the Sun, which along with other indicators suggests the existence of considerable magnetic activity, something unexpected (although not entirely unusual) in a type A star that is also a fast rotator. Stars of this mass no longer have the deep convective envelope typical of the lower main sequence stars, and that is the one that is supposed to keep the magnetic field intense in them.
Due to the precession of the Earth, Alderamin marked the celestial north pole around 20,000 years ago and will point it out again towards the year 7500 of our era.
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