Arcturus
 Arcturus in the constellation of Boötes. |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Boötes |
| Pronunciation | /ɑːrkˈtjʊərəs/ |
| Right ascension | 14h 15m 39.7s |
| Declination | +19° 10′ 56″ |
| Apparent magnitude (V) | −0.05 |
| Characteristics | |
| Spectral type | K0 III |
| Apparent magnitude (J) | −2.25 |
| U−B color index | +1.28 |
| B−V color index | +1.23 |
| R−I color index | +0.65 |
| Note (category: variability): | H and K emission vary. |
| Astrometry | |
| Radial velocity (Rv) | −5.19 km/s |
| Proper motion (μ) |
RA: −1093.45 mas/yr Dec.: −1999.40 mas/yr |
| Parallax (π) | 88.83 ± 0.54mas |
| Distance | 36.7 ± 0.2 ly (11.26 ± 0.07 pc) |
| Absolute magnitude (MV) | −0.30±0.02 |
| Details | |
| Mass | 1.08±0.06 M☉ |
| Radius | 25.4±0.2 R☉ |
| Luminosity | 170 L☉ |
| Surface gravity (log g) | 1.66±0.05 cgs |
| Temperature | 4286±30 K |
| Metallicity [Fe/H] | −0.52±0.04 dex |
| Rotational velocity (v sin i) | 2.4±1.0 km/s |
| Age |
7.1+1.5 −1.2 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
|
Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.), VizieR catalog entry |
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Arcturus (/ɑːrkˈtjʊərəs/), also designated Alpha Boötis (α Boötis, abbreviated Alpha Boo, α Boo) is a star in the constellation of Boötes. It is relatively close at 36.7 light-years from the Sun. Together with Spica and Denebola (or Regulus, depending on the source), Arcturus is part of the Spring Triangle asterism and, by extension, also of the Great Diamond along with the star Cor Caroli.
α Boötis (Latinised to Alpha Boötis) is the star's Bayer designation.
The traditional name Arcturus derives from Ancient Greek Ἀρκτοῦρος (Arktouros) and means "Guardian of the Bear", ultimately from ἄρκτος (arktos), "bear" and οὖρος (ouros), "watcher, guardian". It has been known by this name since at least the time of Hesiod. This is a reference to its being the brightest star in the constellation of Boötes (of which it forms the left foot), which is next to the constellations of Ursa Major and Ursa Minor, the Greater and Lesser Bears.
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 Arcturus for this star. It is now so entered in the IAU Catalog of Star Names.
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