Star Stars · In Ophiuchus
Rasalhague
Rasalhague, α Ophiuchi, is a white giant in Ophiuchus: the 61st brightest star in the night sky.
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- Constellation
- Ophiuchus
- Designation
- α Ophiuchi
- Apparent magnitude
- 2.08 · 61st brightest star in the night sky
- Spectral class
- A5III
- Distance
- 48.6 light-years
- Highest at midnight
- mid June
- Position (J2000)
- RA 17h 35m · Dec +12° 34′
A white giant, around 8,800 K, like Sirius and Vega. About 59× brighter than the faintest star the eye can see. Gives off about 27 times the Sun's visible light. The light you are seeing left in 1977.
When to see it
On the night of Sat 12 Jun 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 18:08 | 01:12 · 51° | 08:16 |
| New York EDT | 18:24 | 01:07 · 62° | 07:50 |
| Singapore GMT+8 | 19:17 | 01:17 · 79° | 07:17 |
| Sydney GMT+10 | 18:43 | 00:08 · 44° | 05:33 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 53° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 42° 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 48.6 light-years away, and shines at magnitude 2.08 in our sky. From that far, the Sun would be a star of magnitude 5.7: 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 2.08 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Vega: Rasalhague is 30° south-west of it, about three fists at arm’s length.
Look for
From 50° north it climbs to 53°; from 35° north it climbs to 68°; from the equator it climbs to 77°; from 35° south it climbs to 42°.
Science
Rasalhague’s surface is about 8,800 K, some 3,000 K hotter than the Sun’s 5,772 K, so its light is strongest at about 330 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 1.2, about as bright as Mimosa looks to us.
Did you know
Against Vega, the brighter star the hop starts from: Vega looks 6.6 times as bright as Rasalhague in our sky; Vega is 25 light-years away and Rasalhague 49 light-years, so side by side Vega would give off 1.8 times as much light as Rasalhague.
Science
Rasalhague is the 16th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Rutilicus, about 21 light-years from it; on our sky the two are 23° apart.
Look for
The Sun passes 36° south of Rasalhague 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 14 hours a day, from 35° north about 13 and from 35° south about 11. It is 23° from the plane of the Milky Way.