Star Stars · In Grus
Alnair
Alnair, α Gruis, is a blue-white subgiant in Grus: the 32nd brightest star in the night sky.
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- Constellation
- Grus
- Designation
- α Gruis
- Apparent magnitude
- 1.73 · 32nd brightest star in the night sky
- Spectral class
- B7IV
- Distance
- 101 light-years
- Highest at midnight
- late August
- Position (J2000)
- RA 22h 08m · Dec −46° 58′
A blue-white subgiant, around 16,000 K, like Rigel and Spica. About 81× 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 1925.
When to see it
On the night of Sat 21 Aug 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | Never rises | ||
| New York EDT | 23:31 | 01:04 · 2° | 02:38 |
| Singapore GMT+8 | 19:22 | 01:15 · 42° | 07:08 |
| Sydney GMT+10 | 15:05 | 00:06 · 77° | 09:07 |
Common questions
- Can I see it from 50° north?
- No. From there it never rises: you would have to travel south of 43° north before it cleared the horizon at all.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 78° up in the south.
- When is the best time of year to see it?
- Around late August, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid November it is highest in the early evening, and in late May not until the hours before dawn.
- How far away is it, and how bright?
- It is 101 light-years away, and shines at magnitude 1.73 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 1.73 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Fomalhaut: Alnair is 20° south-west of it, a spread hand at arm’s length.
Look for
From 50° north it never rises; from 35° north it barely clears the horizon, at 8°; from the equator it climbs to 43°; from 35° south it climbs to 78°.
Science
Alnair’s surface is about 16,000 K, some 10,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 180 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 Fomalhaut, the brighter star the hop starts from: Fomalhaut looks 1.7 times as bright as Alnair in our sky, but Fomalhaut is 25 light-years away and Alnair 101 light-years, so side by side Alnair would give off 9.6 times as much light as Fomalhaut.
Science
Alnair is the 55th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Ankaa, about 43 light-years from it; on our sky the two are 25° apart.
Look for
The Sun passes 33° north of Alnair around mid February, 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 6 hours a day and from 35° south about 18. It is 52° from the plane of the Milky Way, well away from the band.