An ancient Mexican building was angled to face the rising of Capella
Around 275 BC, builders at Monte Albán in Oaxaca set one structure, Building J, askew from everything around it. Its steps were aligned so that someone standing in its doorway would face Capella as it rose. That star's first dawn appearance each year came within a day of the Sun passing directly overhead.
Capella, meaning little goat in Latin, ranks sixth in brightness among night-sky stars and is the closest first-magnitude star to the north celestial pole. From anywhere north of 44 degrees, including all of Britain, it never sets. The Greeks linked it with Amalthea, the goat that nursed Zeus, and associated it with rain; an Akkadian inscription from around the twentieth century BC may mention it, and Bedouin astronomers pictured the surrounding stars as a herd of goats.
To the eye it is one point of yellowish light, but it is really four stars. The bright part consists of two yellow giants, each around 2.5 times the Sun's mass, circling each other every 104 days at roughly the distance between Venus and the Sun. Both have exhausted the hydrogen in their cores; the cooler one is already fusing helium. About 10,000 times Earth's distance from the Sun away orbits a second pair: two faint red dwarfs. Robert Burnham Jr. imagined a scale model in which the giants were balls 13 and 7 inches wide set ten feet apart, while the dwarf pair would sit 21 miles away.
Capella has a string of firsts. William Wallace Campbell at Lick Observatory spotted a second spectrum superimposed on the first and announced in 1899 that it was double. In 1919 John Anderson and Francis Pease at Mount Wilson split the pair using interferometry, the first such measurement of any object beyond the Solar System. In 1995 it became the first object imaged by an interferometer made of separate telescopes, at Cambridge. In 1974 a rocket detected X-rays from it more than 10,000 times stronger than the Sun's, probably from the corona of the larger giant.
Its place in the sky has shifted. Around 237,000 years ago it passed within 29 light years of us, shining about as bright as Canopus does now. Between 210,000 and 160,000 years ago it was the brightest star in the night sky. Today it sits about 42.9 light years away.
Source: Capella
