Theta Eridani
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| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Eridanus |
| Right ascension | 02h 58m 15.70s |
| Declination | −40° 18' 17.0" |
| Apparent magnitude (V) | 3.2 |
| Characteristics | |
| Spectral type | A4 III |
| U-B color index | 0.14 |
| B-V color index | 0.34 |
| Astrometry | |
| Radial velocity (Rv) | 11.9 km/s |
| Proper motion (μ) | RA: −44.6 mas/yr Dec.: 19.0 mas/yr |
| Parallax (π) | 28.00 ± 11.00 mas |
| Distance | ~120 (80–190) ly (~40 (30–60) pc) |
| Absolute magnitude (MV) | -0.59 |
| Other designations | |
| Database references | |
| SIMBAD | data |
Theta Eridani (θ Eri / θ Eridani) is a star in the constellation Eridanus. It has the traditional name Acamar (which means "the last of the river", Arabic Ākhir an-nahr, with a Roman-alphabet handwriting misread "m" for "rn"). Achernar is also the same Arabic word. It is known as 天园六 (the Sixth Star of the Celestial Orchard) in Chinese.
Acamar is a double star, consisting of a +3.2 magnitude bright main star of the spectral class A4 and a companion of the spectral class A1 of magnitude +4.3. The angular separation of the stars amounts to 8.2". The distance from Earth is 120 light-years.
Interestingly, Ptolemy described it as a first-magnitude star and Al Sufi in the 10th century listed it as one of the thirteen brightest stars in the sky, and Ulugh Beg from Persia in the 15th century also listed it as a first-magnitude star.
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