Five astronomers and the new sky

The 20-year-old Tycho and his slightly older cousin Manderup Parsberg fought with rapiers in the dark at Rostock on 29 December 1566 over a mathematical disagreement that had begun at a Christmas engagement party. Tycho lost the bridge of his nose. He wore a metal prosthesis — probably brass with thin gold and silver coating — for the rest of his life.

Comparing his own star positions with Alexandrian measurements 150 years older, Hipparchus found that the celestial coordinate system was drifting westward at approximately one degree per century. Precession is the slow gyroscopic wobble of Earth's axis; the full cycle takes ~26,000 years. He was the first observer to detect any systematic motion of the entire celestial sphere.

Tycho's parallax measurements — comparing the comet's position from his observatory at Uraniborg against another site — showed the comet was much further than the Moon. That meant the comet was moving through what Aristotelian astronomy held to be unchanging crystal spheres, demolishing the medieval cosmology. Elliptical orbits would not be established until Kepler in the early 17th century.

Scheiner observed sunspots from Ingolstadt in March 1611 and published his findings later that year under a pseudonym, interpreting the spots as small satellites orbiting the Sun. Galileo argued they were features on the solar surface and accused Scheiner of theological motivation. Harriot saw spots in England in late 1610 but, in his usual habit, published nothing. The dispute fed Galileo's general conflict with Jesuit astronomy.

The Antikythera mechanism — a bronze geared device recovered from a Roman shipwreck in 1900-1901 — was a hand-cranked analog computer for astronomy. Its 37 gears modelled the lunar orbit, predicted solar and lunar eclipses, tracked planetary positions, and included a 4-year Olympiad counter. It is roughly 1,500 years more sophisticated than the next known geared mechanism.