The astronomer who cast horoscopes

Kepler (1571–1630) is the man who showed that planets move in ellipses, sweep out equal areas in equal times, and take longer to go round the further out they are. Newton built on him. NASA named a planet-hunting telescope after him.

Astrology paid the bills

As a young teacher in Graz, Kepler had to write the town’s annual almanac. His first, for 1595, warned of a bitter cold winter and an attack by the Ottoman Turks. Both came, and his name was made. In Prague, as Imperial Mathematician to Rudolf II, giving astrological advice was part of the job.

A chart for Wallenstein

In 1608 an intermediary asked Kepler for the horoscope of an unnamed young nobleman. It was Albrecht von Wallenstein, then about twenty-five. Kepler described a restless, ambitious, suspicious man who would seek power. Wallenstein became commander of the Emperor’s armies in the Thirty Years’ War, and kept the chart, annotating it in his own hand.

In 1624 he asked Kepler to revise it, and Kepler, warning his client not to rely on the stars for decisions, corrected the birth time and carried the forecast forward. The revised reading runs out in 1634. Wallenstein was murdered on 25 February 1634.

He warned against throwing out the baby with the bathwater.

The third man

Kepler thought most of the astrology of his day was rubbish, and said so. But in a 1610 book, Tertius Interveniens, “the third man intervening,” he warned the sceptics against throwing out the baby with the bathwater: he believed the angles between planets really did stir something in people. He even invented new ones, the quintile (72°) and the sesquiquadrate (135°) among them, which astrologers still use.