Acamar — Double Star in Eridanus
HIP 13847; Theta1 Eridani
About Acamar
Description
Acamar is a binary star system at magnitude 3.24 in Eridanus, consisting of two white stars (A4III and A1V) separated by about 8 arcseconds. Located about 161 light-years from Earth, the pair makes one of the finest double stars in the southern sky.
Observing Tips
Acamar lies in the middle of Eridanus's long winding course. A small telescope reveals a beautiful pair of nearly white stars. Before Achernar was known to European astronomers, Acamar marked the end of the River. Best observed November through February.
History
The name Acamar comes from the Arabic 'akhir al-nahr,' meaning 'the end of the river' — the same root as Achernar. For ancient Greek and Arabic observers at northern latitudes, Acamar was the southernmost visible star of Eridanus, and thus the river's end.
Fun Facts
Acamar once marked the end of Eridanus for classical astronomers who could not see farther south. The discovery of the more southerly Achernar pushed the river's terminus farther toward the south celestial pole.
Observe
1Physical Properties
2Position & Identifiers
3How easy to split?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Multiple Star System
Separation over time
Essentially fixed on human timescales — the same view your grandchildren will see.
Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.
Eyepiece View
A: 3.2 · B: 4.1 · Sep: 8.2″ · PA: 90° · N up, E right
Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″
Explore
7
Size Comparison
8
Compare Stars
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Spectral Classification
10
Hertzsprung-Russell Diagram
11
Stellar Lifecycle
12
Blackbody Spectrum
13
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
14
Stellar Fusion
Discover
15Stellar Notes
16
Light Travel Time Machine
17
Relativistic Travel
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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