Star Stars · In Sagittarius
Ascella
Ascella, ζ Sagittarii, is a white subgiant in Sagittarius: the 103rd brightest star in the night sky.
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- Constellation
- Sagittarius
- Designation
- ζ Sagittarii
- Apparent magnitude
- 2.60 · 103rd brightest star in the night sky
- Spectral class
- A3IV
- Distance
- 88.2 light-years
- Highest at midnight
- early July
- Position (J2000)
- RA 19h 03m · Dec −29° 53′
A white subgiant, around 9,300 K, like Sirius and Vega. About 36× brighter than the faintest star the eye can see. Gives off about 56 times the Sun's visible light. The light you are seeing left around 1938.
When to see it
On the night of Mon 5 Jul 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 22:14 | 01:09 · 9° | 04:04 |
| New York EDT | 21:03 | 01:04 · 19° | 05:05 |
| Singapore GMT+8 | 19:19 | 01:15 · 59° | 07:11 |
| Sydney GMT+10 | 16:36 | 00:06 · 86° | 07:35 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 10° up in the south.
- Can I see it from 35° south?
- Yes, and well placed: at its highest it passes almost overhead, 85° 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 88.2 light-years away, and shines at magnitude 2.60 in our sky. From that far, the Sun would be a star of magnitude 7.0: 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 2.60 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Nunki: Ascella is 3.9° south-east of it, three fingers at arm’s length.
Look for
From 50° north it climbs to 10°; from 35° north it climbs to 25°; from the equator it climbs to 60°; from 35° south it climbs to 85°.
Science
Ascella’s surface is about 9,300 K, some 3,500 K hotter than the Sun’s 5,772 K, so its light is strongest at about 310 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 0.4, about as bright as Achernar looks to us.
Did you know
Against Nunki, the brighter star the hop starts from: Nunki looks 1.7 times as bright as Ascella in our sky; Nunki is 228 light-years away and Ascella 88 light-years, so side by side Nunki would give off 11 times as much light as Ascella.
Science
Ascella is the 45th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Kaus Borealis, about 16 light-years from it; on our sky the two are 8.9° apart.
Look for
The Sun passes 7.2° north of Ascella around early January, 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 6 hours a day, from 35° north about 9 and from 35° south about 15. It is 15° from the plane of the Milky Way.