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.

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.

This makes Arcturus the third-brightest individual star, just ahead of α Centauri A (officially named Rigil Kentaurus), whose apparent magnitude is −0.01.

The star culminates at midnight on April 27, and at 9 p.m. on June 10 being visible during the late northern spring or the southern autumn.

[16] From the northern hemisphere, an easy way to find Arcturus is to follow the arc of the handle of the Big Dipper (or Plough in the UK).

[17][18] Together with the bright stars Spica and Regulus (or Denebola, depending on the source), Arcturus is part of the Spring Triangle asterism.

[15] Based upon an annual parallax shift of 88.83 milliarcseconds, as measured by the Hipparcos satellite, Arcturus is 36.7 light-years (11.26 parsecs) from Earth.

[1] Because of its proximity, Arcturus has a high proper motion, two arcseconds a year, greater than any first magnitude star other than α Centauri.

[3] In the absence of a binary companion, the mass of Arcturus cannot be measured directly, but models suggest it is slightly greater than that of the Sun.

[24] Arcturus has evolved off the main sequence to the red giant branch, reaching an early K-type stellar classification.

As the brightest K-type giant in the sky, it has been the subject of multiple atlases with coverage from the ultraviolet to infrared.

[28] Examination of carbon monoxide lines show the molecular component of the atmosphere extending outward to 2–3 times the radius of the star, with the chromospheric wind steeply accelerating to 35–40 km/s in this region.

[15] As one of the brightest stars in the sky, Arcturus has been the subject of a number of studies in the emerging field of asteroseismology.

[31] Hipparcos satellite astrometry suggested that Arcturus is a binary star, with the companion about twenty times dimmer than the primary and orbiting close enough to be at the very limits of humans' current ability to make it out.

This substellar object would be nearly 12 times the mass of Jupiter and be located roughly at the same orbital distance from Arcturus as the Earth is from the Sun, at 1.1 astronomical units.

[33] One astronomical tradition associates Arcturus with the mythology around Arcas, who was about to shoot and kill his own mother Callisto who had been transformed into a bear.

[38] Arcturus is also mentioned in Plato's "Laws" (844e) as a herald for the season of vintage, specifically figs and grapes.

[43] In Indian astronomy, Arcturus is called Swati or Svati (Devanagari स्वाति, Transliteration IAST svāti, svātī́), possibly 'su' + 'ati' ("great goer", in reference to its remoteness) meaning very beneficent.

The Wotjobaluk Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, mother of Djuit (Antares) and another star in Boötes, Weet-kurrk[45] (Muphrid).

Traveling east and north they eventually crossed the equator and reached the latitude at which Arcturus would appear directly overhead in the summer night sky.

Knowing they had arrived at the exact latitude of the island chain, they sailed due west on the trade winds to landfall.

[50] It was equated to the Tuamotuan constellation Te Kiva, meaning "frigatebird", which could either represent the figure of Boötes or just Arcturus.

[53] In the Marquesas Islands, Arcturus was probably called Tau-tou and was the star that ruled the month approximating January.

star of the plow) was in fact Arcturus, as the constellation of Boötes was called "Ezogh" (Armenian: Եզող; lit.

[59][61][62][63][64][65] In the Middle Ages, Arcturus was considered a Behenian fixed star and attributed to the stone jasper and the plantain herb.

[67] At the height of the American Civil War, President Abraham Lincoln observed Arcturus through a 9.6-inch refractor telescope when he visited the Naval Observatory in Washington, D.C., in August 1863.