Arcturus

For other uses, see Arcturus (disambiguation). "α Boötis" redirects here. For A Boötis, see HD 125351.
Arcturus
Arcturus in the constellation of Boötes (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Pronunciation /ɑːrkˈtjʊərəs/
Right ascension 14h 15m 39.7s[1]
Declination +19° 10′ 56″[1]
Apparent magnitude (V) −0.05[2]
Characteristics
Evolutionary stage Red giant branch[3]
Spectral type K1.5 III Fe−0.5[4]
Apparent magnitude (J) −2.25[2]
U−B color index +1.28[2]
B−V color index +1.23[2]
R−I color index +0.65[2]
Note (category: variability): H and K emission vary.
Astrometry
Radial velocity (Rv)−5.19[5] km/s
Proper motion (μ) RA: −1093.45[6] mas/yr
Dec.: −1999.40[6] mas/yr
Parallax (π)88.83 ± 0.54 mas[1]
Distance36.7 ± 0.2 ly
(11.26 ± 0.07 pc)
Absolute magnitude (MV)−0.30±0.02[7]
Details
Mass1.08±0.06[3] M☉
Radius25.4±0.2[3] R☉
Luminosity170[8] L☉
Surface gravity (log g)1.66±0.05[3] cgs
Temperature4,286±30[3] K
Metallicity [Fe/H]−0.52±0.04[3] dex
Rotational velocity (v sin i)2.4±1.0[7] km/s
Age7.1+1.5
−1.2[3] Gyr
Other designations
Alramech, Alramech, Abramech, α Boötis, Alpha Boo, α Boo, 16 Boötis, BD+19°2777, GJ 541, HD 124897, HIP 69673, HR 5340, SAO 100944, LHS 48, GCTP 3242.00
Database references
SIMBADdata
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.),
VizieR catalog entry

Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05,[2] 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.

Located relatively close at 36.7 light-years from the Sun, Arcturus is a 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 (around 35 million kilometers) and is around 170 times as luminous.

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  3. ^ a b c d e f g Cite error: The named reference ramirez_prieto_2011 was invoked but never defined (see the help page).
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  6. ^ a b Cite error: The named reference Perryman1997 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference aj135_3_892 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference aaa465_2_593 was invoked but never defined (see the help page).