The Chinese Sky

The same seven stars as the Big Dipper, with a different job. In China they are Běidǒu, the Northern Dipper — a ladle, and also the emperor's carriage. Sima Qian, the Han court astronomer, wrote about 90 BCE that it turns about the centre of the sky, oversees the four quarters, divides yin from yang and fixes the seasons. The sky was a state, and this was its chief of staff.

The handle is a clock hand for the year. A text of the Warring States, the Heguanzi, puts it in one line: when the handle points east at dusk it is spring everywhere under heaven; south, summer; west, autumn; north, winter. It works because the whole sky shifts about a degree a night against the clock, and Alkaid at the tip is far enough from the pole to sweep a wide circle.

Around the pole the Chinese drew a walled palace, the Purple Forbidden Enclosure — two arcs of faint stars guarding the emperor of heaven and his household. The emperor was Kochab, three thousand years ago the nearest bright star to the pole; Polaris, well off it then, was an attendant beside the throne. Beijing's Purple Forbidden City is named for this enclosure.

The band of sky the Moon travels was cut into 28 lodges, seven to each quarter, and each quarter has an animal. The east is the Azure Dragon, and it is enormous: its horn is Spica, its heart Antares, and the Scorpion's tail, down to Shaula, is its tail. The other quarters are the Vermilion Bird of the south, the White Tiger of the west and the Black Tortoise of the north.

Antares was Dàhuǒ, the Great Fire, and the oldest calendars were kept by it: the Zuozhuan remembers a Fire Rectifier who watched it at dusk. "In the seventh month, the Fire flows down," a farming ode in the Book of Songs begins: Antares sinking west at dusk meant the heat had broken. The lodge just west of it is Fáng, the Room — a name the IAU has since given its star.

The Milky Way is the Silver River. On one bank is Vega, the Weaver Girl; on the other, Altair, the Cowherd, with Tarazed and Alshain either side — the two children he carries in baskets on a shoulder pole. The Queen Mother of the West drew the river between them; on the seventh night of the seventh month magpies bridge it and they meet. That night is Qīxī — in Japan, Tanabata.

Court astronomers recorded what changed. In May 1006 a guest star appeared here, low in the south below the Root lodge, and stayed visible for over a year; in Cairo it was described as two or three times the size of Venus. It was the brightest supernova in recorded history, and its remnant, 7,000 light-years away, was found in 1965 exactly where the Song records put it.