Star Stars · In Cepheus
Alderamin
Alderamin, α Cephei, is a white subgiant in Cepheus: the 91st brightest star in the night sky.
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- Constellation
- Cepheus
- Designation
- α Cephei
- Apparent magnitude
- 2.45 · 91st brightest star in the night sky
- Spectral class
- A7IV-V
- Distance
- 49.0 light-years
- Highest at midnight
- early August
- Position (J2000)
- RA 21h 19m · Dec +62° 35′
A white subgiant, around 8,300 K, like Sirius and Vega. About 42× brighter than the faintest star the eye can see. Gives off about 20 times the Sun's visible light. The light you are seeing left in 1977.
When to see it
On the night of Sun 8 Aug 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | Never sets | 01:10 · 79° | — |
| New York EDT | Never sets | 01:05 · 68° | — |
| Singapore GMT+8 | 19:06 | 01:15 · 29° | 07:25 |
| Sydney GMT+10 | Never rises | ||
Common questions
- Can I see it from 50° north?
- Yes, on any clear night of the year. From there it never sets: it is circumpolar, circling the pole and still 23° up at its lowest.
- Can I see it from 35° south?
- No. From there it never rises: you would have to travel north of 27° south before it cleared the horizon at all.
- When is the best time of year to see it?
- Around early August, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by early November it is highest in the early evening, and in early May not until the hours before dawn.
- How far away is it, and how bright?
- It is 49.0 light-years away, and shines at magnitude 2.45 in our sky. From that far, the Sun would be a star of magnitude 5.7: one you would need a dark country sky to see at all.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.45 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Deneb: Alderamin is 18° north of it, a spread hand at arm’s length.
Look for
From 50° north and 35° north it is circumpolar and never sets; from the equator it climbs to 27°; from 35° south it never rises.
Science
Alderamin’s surface is about 8,300 K, some 2,500 K hotter than the Sun’s 5,772 K, so its light is strongest at about 350 nm, in the ultraviolet, past the violet end of what the eye can see, where the Sun’s is strongest at 500 nm. Moved to 33 light-years, the distance astronomers compare stars at, it would shine at magnitude 1.6, about as bright as Castor looks to us.
Did you know
Against Deneb, the brighter star the hop starts from: Deneb looks 3.0 times as bright as Alderamin in our sky; Deneb is 1,412 light-years away and Alderamin 49 light-years, so side by side Deneb would give off 2,500 times as much light as Alderamin.
Science
Alderamin is the 17th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Caph, about 19 light-years from it; on our sky the two are 21° apart.
Look for
The Sun passes 69° south of Alderamin around early February, when it is highest at noon, in daylight: the weeks either side are its worst time of year. It is 9° from the plane of the Milky Way, inside the band a dark sky shows.