Star Stars · In Corona Borealis
Alphecca
Alphecca, α Coronae Borealis, is a white main-sequence star in Corona Borealis: the 69th brightest star in the night sky.
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- Constellation
- Corona Borealis
- Designation
- α Coronae Borealis
- Apparent magnitude
- 2.22 · 69th brightest star in the night sky
- Spectral class
- A0V
- Distance
- 75.0 light-years
- Highest at midnight
- mid May
- Position (J2000)
- RA 15h 35m · Dec +26° 43′
A white main-sequence star, around 10,000 K, like Sirius and Vega. About 52× brighter than the faintest star the eye can see. Gives off about 58 times the Sun's visible light. The light you are seeing left in 1951.
When to see it
On the night of Thu 13 May 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 16:35 | 01:10 · 65° | 09:45 |
| New York EDT | 17:24 | 01:04 · 76° | 08:45 |
| Singapore GMT+8 | 19:13 | 01:15 · 65° | 07:17 |
| Sydney GMT+10 | 19:25 | 00:06 · 30° | 04:47 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 67° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 28° up in the north.
- When is the best time of year to see it?
- Around mid 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 75.0 light-years away, and shines at magnitude 2.22 in our sky. From that far, the Sun would be a star of magnitude 6.6: 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 2.22 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Arcturus: Alphecca is 20° north-east of it, a spread hand at arm’s length.
Look for
From 50° north it climbs to 67°; from 35° north it climbs to 82°; from the equator it climbs to 63°; from 35° south it climbs to 28°.
Science
Alphecca’s surface is about 10,000 K, some 4,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 290 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 Procyon looks to us.
Did you know
Against Arcturus, the brighter star the hop starts from: Arcturus looks 8.1 times as bright as Alphecca in our sky; Arcturus is 37 light-years away and Alphecca 75 light-years, so side by side Arcturus would give off 1.9 times as much light as Alphecca.
Science
Alphecca is the 30th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Unukalhai, about 26 light-years from it; on our sky the two are 20° apart.
Look for
The Sun passes 44° south of Alphecca around mid November, 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 17 hours a day, from 35° north about 15 and from 35° south about 9. It is 54° from the plane of the Milky Way, well away from the band.