Star Stars · In Ursa Major
Alkaid
Alkaid, η Ursae Majoris, is a blue-white main-sequence star in Ursa Major: the 40th brightest star in the night sky.
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- Constellation
- Ursa Major
- Designation
- η Ursae Majoris
- Apparent magnitude
- 1.85 · 40th brightest star in the night sky
- Spectral class
- B3V SB
- Distance
- 104 light-years
- Highest at midnight
- mid April
- Position (J2000)
- RA 13h 48m · Dec +49° 19′
A blue-white main-sequence star, around 24,000 K, like Rigel and Spica. About 72× brighter than the faintest star the eye can see. Gives off about 160 times the Sun's visible light. The light you are seeing left around 1922.
When to see it
On the night of Fri 16 Apr 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | Never sets | 01:09 · 88° | — |
| New York EDT | 13:26 | 01:04 · 82° | 12:42 |
| Singapore GMT+8 | 19:09 | 01:14 · 42° | 07:20 |
| Sydney GMT+10 | 21:30 | 00:05 · 7° | 02:41 |
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 9° up at its lowest.
- Can I see it from 35° south?
- Only just. At its highest it is 6° above the northern horizon, so it needs a clear, flat view that way and clean air.
- When is the best time of year to see it?
- Around mid April, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid July it is highest in the early evening, and in mid January not until the hours before dawn.
- How far away is it, and how bright?
- It is 104 light-years away, and shines at magnitude 1.85 in our sky. From that far, the Sun would be a star of magnitude 7.3: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 1.85 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Alioth: Alkaid is 10° south-east of it, a fist at arm’s length.
Look for
From 50° north it is circumpolar and never sets; from 35° north it climbs to 76°; from the equator it climbs to 41°; from 35° south it barely clears the horizon, at 6°.
Science
Alkaid’s surface is about 24,000 K, some 18,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 120 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 −0.7, about as bright as Canopus looks to us.
Did you know
Against Alioth, the brighter star the hop starts from: the two look about as bright as each other in our sky; Alioth is 83 light-years away and Alkaid 104 light-years, so side by side Alkaid would give off 1.5 times as much light as Alioth.
Science
Alkaid is the 56th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Mizar, about 21 light-years from it; on our sky the two are 6.7° apart.
Look for
The Sun passes 54° south of Alkaid around mid October, when it is highest at noon, in daylight: the weeks either side are its worst time of year. From 35° north it is above the horizon for about 19 hours a day and from 35° south about 5. It is 65° from the plane of the Milky Way, well away from the band.