Star Stars · In Ophiuchus
Cebalrai
Cebalrai, β Ophiuchi, is an orange giant in Ophiuchus: the 127th brightest star in the night sky.
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- Constellation
- Ophiuchus
- Designation
- β Ophiuchi
- Apparent magnitude
- 2.76 · 127th brightest star in the night sky
- Spectral class
- K2III
- Distance
- 81.8 light-years
- Highest at midnight
- mid June
- Position (J2000)
- RA 17h 43m · Dec +04° 34′
An orange giant, around 4,900 K, like Arcturus and Aldebaran. About 31× brighter than the faintest star the eye can see. Gives off about 42 times the Sun's visible light. The light you are seeing left around 1944.
When to see it
On the night of Tue 15 Jun 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 18:47 | 01:09 · 43° | 07:31 |
| New York EDT | 18:49 | 01:03 · 54° | 07:18 |
| Singapore GMT+8 | 19:15 | 01:14 · 87° | 07:13 |
| Sydney GMT+10 | 18:18 | 00:05 · 52° | 05:52 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 45° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 50° up in the north.
- When is the best time of year to see it?
- Around mid June, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid September it is highest in the early evening, and in mid March not until the hours before dawn.
- How far away is it, and how bright?
- It is 81.8 light-years away, and shines at magnitude 2.76 in our sky. From that far, the Sun would be a star of magnitude 6.8: 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 2.76 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Rasalhague: Cebalrai is 8.3° south of it, a fist at arm’s length.
Look for
From 50° north it climbs to 45°; from 35° north it climbs to 60°; from the equator it climbs to 85°; from 35° south it climbs to 50°.
Science
Cebalrai’s surface is about 4,900 K, some 900 K cooler than the Sun’s 5,772 K, so its light is strongest at about 590 nm, 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 0.8, about as bright as Altair looks to us.
Did you know
Against Rasalhague, the brighter star the hop starts from: Rasalhague looks 1.9 times as bright as Cebalrai in our sky, but Rasalhague is 49 light-years away and Cebalrai 82 light-years, so side by side Cebalrai would give off 1.5 times as much light as Rasalhague.
Science
Cebalrai is the 38th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Okab, about 32 light-years from it; on our sky the two are 22° apart.
Look for
The Sun passes 28° south of Cebalrai around mid December, 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 13 hours a day, from 35° north about 12 and from 35° south about 12. It is 17° from the plane of the Milky Way.