Alpha Herculis
 Historical view of the Hercules constellation showing Rasalgethi as the α star and "Head of the Kneeler" |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Hercules |
| A | |
| Right ascension | 17h 14m 38.853s |
| Declination | +14° 23′ 25.0″ |
| Apparent magnitude (V) | 3.350(2.7 - 4.0) |
| B | |
| Right ascension | 17h 14m 39.181s |
| Declination | +14° 23′ 23.98″ |
| Apparent magnitude (V) | 5.322 |
| Characteristics | |
| A | |
| Evolutionary stage | AGB |
| Spectral type | M5 Ib-II |
| U−B color index | +1.01 |
| B−V color index | +1.45 |
| Variable type | SRc |
| B | |
| Spectral type | G8III + A9IV-V |
| Astrometry | |
| Proper motion (μ) |
RA: -6.71 mas/yr Dec.: 32.78 mas/yr |
| Parallax (π) | 9.07 ± 1.32mas |
| Distance | approx. 360 ly (approx. 110 pc) |
| Absolute magnitude (MV) | −2.3 + 1.8 + 2.8 |
| Details | |
| A | |
| Mass | 2.5 M☉ |
| Radius | 264 - 303 R☉ |
| Luminosity | 7,244 - 9,333 L☉ |
| Surface gravity (log g) | −0.41 ± 0.19 cgs |
| Temperature | 3,155 - 3,365 K |
| Ba | |
| Mass | ~2.5 M☉ |
| Luminosity | 126 L☉ |
| Temperature | 4,900 K |
| Bb | |
| Mass | ~2 M☉ |
| Luminosity | 26 L☉ |
| Temperature | 7,350 K |
| Age | 0.41 - 1.25 Gyr |
| Other designations | |
| A: HD 156014, HR 6406, SAO 102680 | |
| B: HD 156015, HR 6407, SAO 102681 | |
| Database references | |
| SIMBAD | data |
Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. When viewed through a telescope, this system is resolved into a number of components, the brightest one of which has been named Rasalgethi.
α Herculis (Latinised to Alpha Herculis) is the system's Bayer designation and 64 Herculis its Flamsteed designation. The two components are designated α¹ Herculis (the brightest of the two) and α² Herculis. The latter is itself a binary star and all three stars are sometimes designated α Herculis A, Ba and Bb, respectively.
The system bore the traditional name Rasalgethi or Ras Algethi (Arabic: رأس الجاثي ra‘is al-jāthī 'Head of the Kneeler'). 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Rasalgethi for α¹ Herculis.
The term ra's al-jaθiyy or Ras al Djathi appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, which was translated into Latin as Caput Ingeniculi.
In Chinese astronomy, Rasalgethi is called 帝座, Pinyin: Dìzuò, meaning 'Emperor's Seat', this star is marking itself and stands alone in the center of the Emperor's Seat asterism, Heavenly Market enclosure (see : Chinese constellations). 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning
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