Star Stars · In Scorpius
Acrab
Acrab, β¹ Scorpii, is a blue-white main-sequence star in Scorpius: the 95th brightest star in the night sky.
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- Constellation
- Scorpius
- Designation
- β¹ Scorpii
- Apparent magnitude
- 2.50 · 95th brightest star in the night sky
- Spectral class
- B0.5V
- Distance
- 404 light-years
- Highest at midnight
- late May
- Position (J2000)
- RA 16h 05m · Dec −19° 48′
A blue-white main-sequence star, around 29,000 K, like Rigel and Spica. About 40× brighter than the faintest star the eye can see. Gives off about 1,300 times the Sun's visible light. The light you are seeing left around 1622.
When to see it
On the night of Fri 21 May 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 20:58 | 01:09 · 19° | 05:21 |
| New York EDT | 20:17 | 01:04 · 29° | 05:51 |
| Singapore GMT+8 | 19:18 | 01:15 · 69° | 07:12 |
| Sydney GMT+10 | 17:11 | 00:06 · 76° | 07:01 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 20° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 75° up in the north.
- When is the best time of year to see it?
- Around late May, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid August it is highest in the early evening, and in mid February not until the hours before dawn.
- How far away is it, and how bright?
- It is 404 light-years away, and shines at magnitude 2.50 in our sky. From that far, the Sun would be a star of magnitude 10.3: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.50 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Dschubba: Acrab is 3.1° north-east of it, two fingers at arm’s length.
Look for
From 50° north it climbs to 20°; from 35° north it climbs to 35°; from the equator it climbs to 70°; from 35° south it climbs to 75°.
Science
Acrab’s surface is about 29,000 K, some 23,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 100 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 −3.0, brighter than Sirius, the brightest star in our sky.
Did you know
Against Dschubba, the brighter star the hop starts from: the two look about as bright as each other in our sky; Dschubba is 491 light-years away and Acrab 404 light-years, so side by side Dschubba would give off 1.8 times as much light as Acrab.
Science
Acrab is the 117th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Saik, about 89 light-years from it; on our sky the two are 12° apart.
Look for
Acrab lies 1.0° north 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 mid November, and for weeks either side it is lost in the glare. From 50° north it is above the horizon for about 9 hours a day, from 35° north about 10 and from 35° south about 14. It is 24° from the plane of the Milky Way.