Tau Herculis
 Historical view of the Hercules constellation showing Rukbalgethi Shemali (τ Her) as the "northern knee" |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Hercules |
| Right ascension | 16h 19m 44.4368s[1] |
| Declination | 46° 18′ 48.119″[1] |
| Apparent magnitude (V) | 3.89[1] |
| Characteristics | |
| Spectral type | B5 IV[1] |
| U−B color index | -0.57[2] |
| B−V color index | -0.155[2] |
| Astrometry | |
| Radial velocity (Rv) | -13.8[1] km/s |
| Proper motion (μ) | RA: -13.15[1] mas/yr Dec.: 39.31[1] mas/yr |
| Parallax (π) | 10.37 ± 0.53[3] mas |
| Distance | 310 ± 20 ly (96 ± 5 pc) |
| Absolute magnitude (MV) | -1.03 |
| Details | |
| Mass | 4.9[4] M☉ |
| Radius | 3.55 ± 0.19[5] R☉ |
| Luminosity | 700[4] L☉ |
| Surface gravity (log g) | 4.02 ± 0.05[5] cgs |
| Temperature | 15,615 ± 301[5] K |
| Metallicity [Fe/H] | 0.15[6] dex |
| Rotational velocity (v sin i) | 46[7] km/s |
| Age | 1[4] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Coordinates: 
16h 19m 44.437s, +46° 18′ 48.12″
Tau Herculis (τ Her, τ Herculis) is a fourth-magnitude star in the constellation Hercules. Its traditional name Rukbalgethi Shemali, though seldom used today in scientific journals, means the "northern knee". It is a blue subgiant star, seven hundred times more luminous than the Sun.
Contents
Properties
Tau Herculis is a blue subgiant star with stellar classification B5IV. Its mass is 4.9 times solar.[4] Though its apparent magnitude is only 3.89, like all B-class stars, it is very luminous boasting a total bolometric luminosity that is 700 times solar.[4] Hipparcos estimated its distance at roughly 96 parsecs from Earth, or 310 ± 20 light years away.
Etymology
Its traditional name Rukbalgethi Shemali is of Arabic origin and shares certain etymological characteristics with the stars Ruchbah and Zubeneschamali signifying Hercules' "northern knee".[8] The star was the north pole star around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession.[4]
In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis, μ1 Boötis and δ Boötis.[9] Consequently, τ Herculis itself is known as 七公二 (Qī Gōng èr, English: the Second Star of Seven Excellencies.)[10]
See also
- Lists of stars in the constellation Hercules
- Class B Stars
- Subgiant star
References
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- ↑ (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 6 月 26 日
