# Alderamin (Alpha Cephei)

Alderamin (Alpha Cephei) is a star in the constellation Cepheus, magnitude 2.5.

**The king’s right arm — a white star spinning in under 12 hours, and a future North Star.**

Alderamin is a contraction of the Arabic al-dhirā‘ al-yamīn, “the right arm”, of King Cepheus. It is waiting for a bigger role. As Earth’s axis slowly wobbles, the north celestial pole wanders among the stars, and around AD 7500 Alderamin will take over as the North Star.

It spins at least 246 km per second at its equator, turning once in under 12 hours; the Sun takes almost a month. The spin flattens it, so its equator is about 27 per cent wider than its poles, and leaves the equator near 6,600 kelvin against 8,600 at the poles.

This white [star](https://astropilot.space/glossary/star) is just beginning to leave its long hydrogen-burning life and will probably become a red giant. Surprisingly for such a fast spinner, it gives off about as much X-ray light as the Sun, a sign of strong magnetic activity. It also pulses very faintly in two different ways at once.

Alderamin (Alpha Cephei) is 49 light-years away: the light we see from it set off in 1977, 8 years after Apollo 11 landed on the Moon.

## Did you know?

- **A pole star for Mars.** Mars’s north pole points to the middle of the line joining Alderamin and Deneb — so the two serve as pole stars of a sort for the red planet.
- **Stars of the Flock.** Ulugh Beg grouped it with Alfirk and Alkidr, two other stars of Cepheus, as al-Kawākib al-Firq, “the Stars of the Flock”.
- **A novel’s namesake.** The Japanese light novel series Alderamin on the Sky takes its name from the star.

A white 2nd-magnitude star, the brightest in Cepheus, at the corner of the king’s house-shaped figure nearest Deneb. It is easy to spot even from light-polluted towns.

## When and where to see it

It is best placed in the evening sky around September, when it crosses the meridian at about 10 pm local time (around midnight in August). It can be seen from everywhere north of 27°S and never sets north of 27°N.

At its highest it stands 77° up from 50°N, 62° up from 35°N, 27° up from the equator, below the horizon from 35°S.

## Facts

- Type: Star
- Constellation: Cepheus
- Designations: Alpha Cephei, α Cep, 5 Cep, HR 8162, HD 203280, HIP 105199
- Magnitude: 2.5
- Position: RA 21h 18.6m, Dec +62° 35′ (J2000)
- Spectral type: A8Vn
- Colour: yellow-white (B−V 0.22)
- Distance: 49 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Alderamin (Alpha Cephei) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/alderamin