Star Stars · In Sagittarius
Nunki
Nunki, σ Sagittarii, is a blue-white main-sequence star in Sagittarius: the 54th brightest star in the night sky.
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- Constellation
- Sagittarius
- Designation
- σ Sagittarii
- Apparent magnitude
- 2.05 · 54th brightest star in the night sky
- Spectral class
- B2.5V
- Distance
- 228 light-years
- Highest at midnight
- early July
- Position (J2000)
- RA 18h 55m · Dec −26° 18′
A blue-white main-sequence star, around 25,000 K, like Rigel and Spica. About 60× brighter than the faintest star the eye can see. Gives off about 620 times the Sun's visible light. The light you are seeing left around 1798.
When to see it
On the night of Sat 3 Jul 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 21:44 | 01:10 · 12° | 04:36 |
| New York EDT | 20:46 | 01:05 · 23° | 05:23 |
| Singapore GMT+8 | 19:19 | 01:15 · 62° | 07:12 |
| Sydney GMT+10 | 16:50 | 00:06 · 82° | 07:22 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 14° up in the south.
- Can I see it from 35° south?
- Yes, and well placed: at its highest it passes almost overhead, 81° up, above most of the air’s haze.
- When is the best time of year to see it?
- Around early July, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by early October it is highest in the early evening, and in early April not until the hours before dawn.
- How far away is it, and how bright?
- It is 228 light-years away, and shines at magnitude 2.05 in our sky. From that far, the Sun would be a star of magnitude 9.0: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.05 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Kaus Australis: Nunki is 11° north-east of it, a fist at arm’s length.
Look for
From 50° north it climbs to 14°; from 35° north it climbs to 29°; from the equator it climbs to 64°; from 35° south it climbs to 81°.
Science
Nunki’s surface is about 25,000 K, some 19,200 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 −2.2, brighter than Sirius, the brightest star in our sky.
Did you know
Against Kaus Australis, the brighter star the hop starts from: Kaus Australis looks 1.3 times as bright as Nunki in our sky, but Kaus Australis is 143 light-years away and Nunki 228 light-years, so side by side Nunki would give off 2.0 times as much light as Kaus Australis.
Science
Nunki is the 89th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Kaus Australis, about 91 light-years from it; on our sky the two are 11° apart.
Look for
Nunki lies 3.4° south of the ecliptic, close enough to the Sun’s path that the Moon can pass in front of it and the planets pass near it. The Sun goes by around early January, and for weeks either side it is lost in the glare. From 50° north it is above the horizon for about 7 hours a day, from 35° north about 9 and from 35° south about 15. It is 12° from the plane of the Milky Way.