Theta Eridani
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation | Eridanus |
| Right ascension | 02h 58m 15.70s |
| Declination | −40° 18' 17.0" |
| Apparent magnitude (V) | 3.2 |
| Spectral Characteristics | |
| Spectral type | A4 III |
| U-B color index | 0.14 |
| B-V color index | 0.34 |
| Variable type | |
| 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) |
| Other designations | |
| Database references | |
| SIMBAD | data |
Theta Eridani (θ Eri / θ Eridani) is a star in the constellation Eridanus. It also has the traditional name Acamar (which means "end of the river", Arabic Ākhir an-nahr, with a Roman-alphabet handwriting misread "m" for "rn"). It is known as 天园六 (the Sixth Star of the Celestrial 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 in the 15th century also listed it as a first-magnitude star.
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