Star Stars · In Eridanus
Acamar
Acamar, θ¹ Eridani, is a white giant in Eridanus: the 154th brightest star in the night sky.
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- Constellation
- Eridanus
- Designation
- θ¹ Eridani
- Apparent magnitude
- 2.88 · 154th brightest star in the night sky
- Spectral class
- A4III+
- Distance
- 161 light-years
- Highest at midnight
- early November
- Position (J2000)
- RA 02h 58m · Dec −40° 18′
A white giant, around 9,000 K, like Sirius and Vega. About 28× brighter than the faintest star the eye can see. Gives off about 140 times the Sun's visible light. The light you are seeing left around 1865.
When to see it
On the night of Mon 2 Nov 2026, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT | Never rises | ||
| New York EST | 21:12 | 00:05 · 9° | 02:58 |
| Singapore GMT+8 | 19:21 | 01:16 · 48° | 07:10 |
| Sydney GMT+11 | 16:50 | 01:06 · 84° | 09:23 |
Common questions
- Can I see it from 50° north?
- No. From there it never rises: you would have to travel south of 49° north before it cleared the horizon at all.
- Can I see it from 35° south?
- Yes, and well placed: at its highest it passes almost overhead, 85° up, above most of the air’s haze.
- When is the best time of year to see it?
- Around early November, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by early February it is highest in the early evening, and in early August not until the hours before dawn.
- How far away is it, and how bright?
- It is 161 light-years away, and shines at magnitude 2.88 in our sky. From that far, the Sun would be a star of magnitude 8.3: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.88 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Achernar: Acamar is 21° north-east of it, a spread hand at arm’s length.
Look for
From 50° north it never rises; from 35° north it climbs to 15°; from the equator it climbs to 50°; from 35° south it climbs to 85°.
Science
Acamar’s surface is about 9,000 K, some 3,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 320 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 −0.6, about as bright as Canopus looks to us.
Did you know
Against Achernar, the brighter star the hop starts from: Achernar looks 9.4 times as bright as Acamar in our sky; Achernar is 139 light-years away and Acamar 161 light-years, so side by side Achernar would give off 7.0 times as much light as Acamar.
Science
Acamar is the 74th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Achernar, about 60 light-years from it; on our sky the two are 21° apart.
Look for
The Sun passes 54° north of Acamar around early May, when it is highest at noon, in daylight: the weeks either side are its worst time of year. From 35° north it is above the horizon for about 7 hours a day and from 35° south about 17. It is 61° from the plane of the Milky Way, well away from the band.