Tau Hydrae
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 9h 29m 8.9s |
| Declination | -2° 46' 8" |
| Apparent magnitude (V) | +4.59 |
| Distance | 56 ly (17.18 pc) |
| Spectral type | F6V |
| Other designations | |
The Bayer designation Tau Hydrae (τ Hya, τ Hydrae) is shared by two star systems, τ¹ Hydrae and τ² Hydrae, in the constellation Hydra. The two stars are separated by 1.74° in the sky.
This star (τ¹ Hya and τ² Hya), along with ι Hya and the 5th‑magnitude 33 Hya (A Hydrae), were Ptolemy's Καμπή (Kampē); but Kazwini knew them as ʽUḳdah, the Knot.[1]
τ¹ Hydrae
Tau-1 Hydrae is a binary star lying 56 light years from Earth. It is a spectral type F6 main sequence star which has an apparent magnitude of +4.59.
τ² Hydrae
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 9h 31m 58.9s |
| Declination | -1° 11' 6" |
| Apparent magnitude (V) | +4.54 |
| Distance | 460 ly (141.10 pc) |
| Spectral type | A3V |
| Other designations | |
Tau-2 Hydrae is a spectral type A3 main sequence star which has an apparent magnitude of +4.54. It is about 460 light years from Earth.
Name
According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Uḳdah were the title for four stars :τ¹ Hya as Uḳdah I, τ² Hya as Uḳdah II, 33 Hya (A Hydrae) as Uḳdah III and ι Hya as Uḳdah IV [2]
In Chinese, 柳宿 (Xīng Sù), meaning Star (asterism), refers to an asterism consisting of τ¹ Hydra and τ² Hydra, Alphard, ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428.[3] Consequently, τ¹ Hydra and τ² themself is known as 星宿二 (Xīng Sù èr, English: the Second Star of Star and 星宿三 (Xīng Sù sān, English: the Third Star of Star.)[4]
References
- "HD 81997 -- Variable Star". SIMBAD Astronomical Database. Retrieved 2006-11-05.
- "HD 82446 -- Variable Star". SIMBAD Astronomical Database. Retrieved 2006-11-05.
- ↑ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 250. ISBN 0-486-21079-0. Retrieved 2010-12-12.
- ↑ Jack W. Rhoads - Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971
- ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 29 日