Star Stars · In Ophiuchus
Yed Prior
Yed Prior, δ Ophiuchi, is a red giant in Ophiuchus: the 120th brightest star in the night sky.
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- Constellation
- Ophiuchus
- Designation
- δ Ophiuchi
- Apparent magnitude
- 2.73 · 120th brightest star in the night sky
- Spectral class
- M1III
- Distance
- 171 light-years
- Highest at midnight
- late May
- Position (J2000)
- RA 16h 14m · Dec −03° 42′
A red giant, around 3,600 K, like Betelgeuse and Antares. About 32× brighter than the faintest star the eye can see. Gives off about 190 times the Sun's visible light. The light you are seeing left around 1855.
When to see it
On the night of Sun 23 May 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 19:30 | 01:10 · 35° | 06:50 |
| New York EDT | 19:19 | 01:05 · 46° | 06:51 |
| Singapore GMT+8 | 19:17 | 01:16 · 85° | 07:14 |
| Sydney GMT+10 | 17:57 | 00:07 · 60° | 06:16 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 36° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 59° 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 late August it is highest in the early evening, and in late February not until the hours before dawn.
- How far away is it, and how bright?
- It is 171 light-years away, and shines at magnitude 2.73 in our sky. From that far, the Sun would be a star of magnitude 8.4: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.73 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Saik: Yed Prior is 8.9° north-west of it, a fist at arm’s length.
Look for
From 50° north it climbs to 36°; from 35° north it climbs to 51°; from the equator it climbs to 86°; from 35° south it climbs to 59°.
Science
Yed Prior’s surface is about 3,600 K, some 2,200 K cooler than the Sun’s 5,772 K, so its light is strongest at about 800 nm, in the infrared, past the red 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 −0.9.
Did you know
Against Saik, the brighter star the hop starts from: the two look about as bright as each other in our sky; Saik is 366 light-years away and Yed Prior 171 light-years, so side by side Saik would give off 5.5 times as much light as Yed Prior.
Science
Yed Prior is the 78th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Zubeneschamali, about 49 light-years from it; on our sky the two are 15° apart.
Look for
The Sun passes 17° south of Yed Prior around late 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 11 hours a day, from 35° north about 12 and from 35° south about 12. It is 32° from the plane of the Milky Way.