Star Stars · In Andromeda
Alpheratz
Alpheratz, α Andromedae, is a blue-white star in Andromeda: the 56th brightest star in the night sky.
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- Constellation
- Andromeda
- Designation
- α Andromedae
- Apparent magnitude
- 2.07 · 56th brightest star in the night sky
- Spectral class
- B9p
- Distance
- 97.0 light-years
- Highest at midnight
- mid September
- Position (J2000)
- RA 00h 08m · Dec +29° 05′
A blue-white star, around 12,000 K, like Rigel and Spica. About 59× brighter than the faintest star the eye can see. Gives off about 110 times the Sun's visible light. The light you are seeing left around 1929.
When to see it
On the night of Mon 20 Sep 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 16:14 | 01:11 · 68° | 10:09 |
| New York EDT | 17:12 | 01:06 · 79° | 09:00 |
| Singapore GMT+8 | 19:15 | 01:17 · 62° | 07:19 |
| Sydney GMT+10 | 19:37 | 00:08 · 27° | 04:38 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 69° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 26° up in the north.
- When is the best time of year to see it?
- Around mid September, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late December it is highest in the early evening, and in late June not until the hours before dawn.
- How far away is it, and how bright?
- It is 97.0 light-years away, and shines at magnitude 2.07 in our sky. From that far, the Sun would be a star of magnitude 7.2: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.07 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Hamal: Alpheratz is 27° west of it, about three fists at arm’s length.
Look for
From 50° north it climbs to 69°; from 35° north it climbs to 84°; from the equator it climbs to 61°; from 35° south it climbs to 26°.
Science
Alpheratz’s surface is about 12,000 K, some 6,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 240 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 −0.3, about as bright as Rigil Kentaurus looks to us.
Did you know
Against Hamal, the brighter star the hop starts from: the two look about as bright as each other in our sky; Hamal is 66 light-years away and Alpheratz 97 light-years, so side by side Alpheratz would give off 2.1 times as much light as Hamal.
Science
Alpheratz is the 53rd nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Hamal, about 49 light-years from it; on our sky the two are 27° apart.
Look for
The Sun passes 26° south of Alpheratz around late March, when it is highest at noon, in daylight: the weeks either side are its worst time of year. From 50° north it is above the horizon for about 17 hours a day, from 35° north about 15 and from 35° south about 9. It is 33° from the plane of the Milky Way.