Tycho Brahe: Wrong, but Points for Creativity

Tycho Brahe was either the best or worst celestial mechanic of all time.
(“Celestial mechanic” isn’t a term, but it should be.)

The late 16th century was an eventful time for astronomy. Fifty years earlier, Copernicus had published De revolutionibus orbium coelestium and introduced the heliocentric model to Europe. (There had been heliocentrists before then, in Greece, India, and elsewhere, but none had been widely accepted.) By the time Tycho was formulating his model in the 1580s, the Church was in an uproar and astronomers were torn between science and politics.

Tycho’s friend Kepler was a heliocentrist, and tried hard to convert him, but Tycho insisted that, if Earth orbited the Sun, the stars should appear to change position throughout the year (this is called stellar parallax and is an invaluable tool to modern astronomers, but nobody in the 1500s had a telescope that could clearly show the tiny shift. Tycho’s real mistake was underestimating the incredible distance to the stars.) Tycho wasn’t giving up on geocentric models, but all his data looked heliocentric.

The result was the Tychonic model of the solar system, in which the planets orbit the Sun and the Sun orbits the Earth. The brilliant part is that this is geometrically identical to an accurate heliocentric model with the entire solar system moving in a circle to cancel out the Earth’s motion. Therefore, every observation Tycho made confirmed his system, strange as it was.

Tycho was a colorful guy; he was wealthy enough to buy 1/100 of Denmark, had at least one gold-and-silver prosthetic nose, and owned a tame moose until it got hammered at a party and fell down a flight of stairs. (no, really!)

Tycho also accidentally put the nail in the geocentric coffin. His extensive and precise observations were grabbed up by his buddy Kepler after his death. Kepler then created the first truly accurate model of the solar system, with elliptical orbits and precise mathematical laws. (Copernicus used the old trick of epicycles because he had a thing for circles and didn’t want to go elliptical) Much later, Isaac Newton would revolutionize celestial mechanics by inventing calculus, gravity, and the Internet. Sadly, he lost his notes on the latter, but that’s a story for another time.