At −1.1, Aldebaran was brightest before this period; it and Capella were situated rather close to each other in the sky and approximated boreal pole stars at the time.

[36] Its goat-associated symbolism dates back to Mesopotamia as a constellation called "GAM", "Gamlum" or "MUL.GAM" in the 7th-century BC document MUL.APIN.

[39] Building J of the pre-Columbian site Monte Albán in Oaxaca state in Mexico was built around 275 BC, at a different orientation to other structures in the complex.

Capella is significant as its heliacal rising took place within a day of the Sun passing directly overhead over Monte Albán.

[40] Professor William Wallace Campbell of the Lick Observatory announced that Capella was binary in 1899, based on spectroscopic observations—he noted on photographic plates taken from August 1896 to February 1897 that a second spectrum appeared superimposed over the first, and that there was a doppler shift to violet in September and October and to red in November and February—showing that the components were moving toward and away from the Earth (and hence orbiting each other).

[41][42] Almost simultaneously, British astronomer Hugh Newall had observed its composite spectrum with a four prism spectroscope attached to a 25-inch (64 cm) telescope at Cambridge in July 1899, concluding that it was a binary star system.

[44] Known as "The Interferometrist's Friend", it was first resolved interferometrically in 1919 by John Anderson and Francis Pease at Mount Wilson Observatory, who published an orbit in 1920 based on their observations.

[47] A high-precision orbit was published in 1994 based on observations by the Mark III Stellar Interferometer, again at Mount Wilson Observatory.

[50] In February 1936, Carl L. Stearns observed that this companion appeared to be double itself;[51] this was confirmed in September that year by Gerard Kuiper.

[55] A rocket flight on that date briefly calibrated its attitude control system when a star sensor pointed the payload axis at Capella.

[57] With an average apparent magnitude of +0.08, Capella is the brightest object in the constellation Auriga, the sixth-brightest star in the night sky, the third-brightest in the northern celestial hemisphere (after Arcturus and Vega), and the fourth-brightest visible to the naked eye from the latitude 40°N.

[59][note 3] Its northern declination is such that it is actually invisible south of latitude 44°S—this includes southernmost New Zealand, Argentina and Chile as well as the Falkland Islands.

Capella and Vega are on opposite sides of the pole, at about the same distance from it, such that an imaginary line between the two stars will nearly pass through Polaris.

Members of the group are of a similar age, and those that are around 2.5 times as massive as the Sun have moved off the main sequence after exhausting their core hydrogen reserves and are expanding and cooling into red giants.

[12] American astronomer Robert Burnham Jr. described a scale model of the system where Capella A was represented by spheres 13 and 7 inches across, separated by ten feet.

[68] Capella A consists of two yellow evolved stars that have been calculated to orbit each other every 104.02128 ± 0.00016 days, with a semimajor axis of 111.11 ± 0.10 million km (0.74272 ± 0.00069 AU), roughly the distance between Venus and the Sun.

[9] The most recent specific published types are K0III and G1III,[70] although older values are still widely quoted such as G5IIIe + G0III from the Bright Star Catalogue[3] or G8III + G0III by Eggen.

They have very nearly equal brightness in the visible light spectrum, with the hotter secondary component generally being found to be a few tenths of a magnitude brighter.

[12] Estimated to be 590 to 650 million years old,[12] the stars were probably at the hot end of spectral class A during their main-sequence lifetime, similar to Vega.

Detailed analysis shows that it is nearing the end of this stage and starting to expand again which will lead it to the asymptotic giant branch.

Capella Aa has slowed until it is rotationally locked to the orbital period, although theory predicts that it should still be rotating more quickly from a starting point of a rapidly-spinning main sequence A star.

[11] Unusually for RS CVn systems, the hotter star, Capella Ab, has the more active atmosphere because it is located in the Hertzsprung gap—a stage where it is changing its angular momentum and deepening its convection zone.

[80] V538 Aurigae and its close companion HD 233153 are red dwarfs ten degrees away from Capella; they have very similar space motions but the small difference makes it possible that this is just a coincidence.

[83] The three Haedi had been identified as a separate constellation by Pliny the Elder and Manilius, and were called Capra, Caper, or Hircus, all of which relate to its status as the "goat star".

[89] Conversely in Slavic Macedonian folklore, Capella was Jastreb "the hawk", flying high above and ready to pounce on Mother Hen (the Pleiades) and the Rooster (Nath).

[38] In the Middle Ages, it was considered a Behenian fixed star, with the stone sapphire and the plants horehound, mint, mugwort and mandrake as attributes.

[25] In Tahitian folklore, Capella was Tahi-ari'i, the wife of Fa'a-nui (Auriga) and mother of prince Ta'urua (Venus) who sails his canoe across the sky.

[98] The Gwich'in saw Capella and Menkalinan has forming shreets'ą įį vidzee, the right ear of the large circumpolar constellation Yahdii, which covered much of the night sky, and whose orientation facilitated navigation and timekeeping.

[99] In Australian Aboriginal mythology for the Boorong people of Victoria, Capella was Purra, the kangaroo, pursued and killed by the nearby Gemini twins, Yurree (Castor) and Wanjel (Pollux).

[100] The Wardaman people of northern Australia knew the star as Yagalal, a ceremonial fish scale, related to Guwamba the barramundi (Aldebaran).