Star Stars · In Serpens
Unukalhai
Unukalhai, α Serpentis, is an orange giant in Serpens: the 105th brightest star in the night sky.
Save the chart (SVG) Tactile chart (A4 SVG)
- Constellation
- Serpens
- Designation
- α Serpentis
- Apparent magnitude
- 2.63 · 105th brightest star in the night sky
- Spectral class
- K2III
- Distance
- 74.0 light-years
- Highest at midnight
- mid May
- Position (J2000)
- RA 15h 44m · Dec +06° 26′
An orange giant, around 4,900 K, like Arcturus and Aldebaran. About 35× brighter than the faintest star the eye can see. Gives off about 38 times the Sun's visible light. The light you are seeing left in 1952.
When to see it
On the night of Sat 15 May 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 18:41 | 01:12 · 45° | 07:43 |
| New York EDT | 18:45 | 01:06 · 56° | 07:27 |
| Singapore GMT+8 | 19:17 | 01:17 · 85° | 07:17 |
| Sydney GMT+10 | 18:26 | 00:08 · 50° | 05:50 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 46° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 49° 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 74.0 light-years away, and shines at magnitude 2.63 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 2.63 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Zubeneschamali: Unukalhai is 17° north-east of it, a fist and a half at arm’s length.
Look for
From 50° north it climbs to 46°; from 35° north it climbs to 61°; from the equator it climbs to 84°; from 35° south it climbs to 49°.
Science
Unukalhai’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 0.9, about as bright as Aldebaran looks to us.
Did you know
Against Zubeneschamali, the brighter star the hop starts from: the two look about as bright as each other in our sky; Zubeneschamali is 185 light-years away and Unukalhai 74 light-years, so side by side Zubeneschamali would give off 6.4 times as much light as Unukalhai.
Science
Unukalhai is the 29th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Alphecca, about 26 light-years from it; on our sky the two are 20° apart.
Look for
The Sun passes 26° south of Unukalhai 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 13 hours a day, from 35° north about 13 and from 35° south about 11. It is 44° from the plane of the Milky Way.