Star Stars · In Ursa Major
Alioth
Alioth, ε Ursae Majoris, is a white star in Ursa Major: the 35th brightest star in the night sky.
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- Constellation
- Ursa Major
- Designation
- ε Ursae Majoris
- Apparent magnitude
- 1.76 · 35th brightest star in the night sky
- Spectral class
- A0p
- Distance
- 82.6 light-years
- Highest at midnight
- early April
- Position (J2000)
- RA 12h 54m · Dec +55° 58′
A white star, around 10,000 K, like Sirius and Vega. About 79× 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 1943.
When to see it
On the night of Fri 2 Apr 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | Never sets | 01:11 · 86° | — |
| New York EDT | Never sets | 01:06 · 75° | — |
| Singapore GMT+8 | 19:09 | 01:16 · 36° | 07:23 |
| Sydney GMT+11 | 00:32 | 01:07 · 0° | 01:42 |
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 16° up at its lowest.
- Can I see it from 35° south?
- No. From there it never rises: you would have to travel north of 34° south before it cleared the horizon at all.
- When is the best time of year to see it?
- Around early April, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by early July it is highest in the early evening, and in early January not until the hours before dawn.
- How far away is it, and how bright?
- It is 82.6 light-years away, and shines at magnitude 1.76 in our sky. From that far, the Sun would be a star of magnitude 6.8: 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 1.76 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Arcturus: Alioth is 40° north of it, about two spread hands at arm’s length.
Look for
From 50° north and 35° north it is circumpolar and never sets; from the equator it climbs to 34°; from 35° south it never rises.
Science
Alioth’s surface is about 10,000 K, some 4,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 290 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 Arcturus, the brighter star the hop starts from: Arcturus looks 5.3 times as bright as Alioth in our sky; Arcturus is 37 light-years away and Alioth 83 light-years, so side by side they would give off about as much light.
Science
Alioth is the 39th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Alcor, about 7 light-years from it; on our sky the two are 4.5° apart.
Look for
The Sun passes 54° south of Alioth around early October, when it is highest at noon, in daylight: the weeks either side are its worst time of year. It is 61° from the plane of the Milky Way, well away from the band.