Arcturus
Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05, it is the fourth-brightest star in the night sky, and the brightest in the northern celestial hemisphere. The name Arcturus originated from ancient Greece; it was then cataloged as α Boötis by Johann Bayer in 1603, which is Latinized to Alpha Boötis. Arcturus forms one corner of the Spring Triangle asterism.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Pronunciation | /ɑːrkˈtjʊərəs/ |
| Right ascension | 14h 15m 39.7s |
| Declination | +19° 10′ 56″ |
| Apparent magnitude (V) | −0.05 |
| Characteristics | |
| Spectral type | K1.5 III Fe−0.5 |
| 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 ± 0.54 mas |
| 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 | 4,286±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 | |
Located relatively close at 36.7 light-years from the Sun, Arcturus is a single red giant of spectral type K1.5III—an aging star around 7.1 billion years old that has used up its core hydrogen and evolved off the main sequence. It is about the same mass as the Sun, but has expanded to 25 times its size and is around 170 times as luminous. Its diameter is 35 million kilometres. Thus far no companion has been detected.