Johannes Kepler (1571–1630) was a German astronomer and mathematician who figured out the exact shape of the heavens by sheer, stubborn number-crunching — decades of it, done by hand, in an era with no telescopes worth the name and a life full of disasters. Sickly, short-sighted, and forever short of money, he still worked out how the planets actually move.
Kepler discovered that planets don't travel in perfect circles, as everyone had assumed for two
thousand years — they trace ellipses, with the Sun sitting slightly off-centre. His
three laws of
Kepler inherited a mountain of ultra-precise planetary observations from the astronomer Tycho Brahe. When he tried to fit Mars to a circle, his answer was off by a mere eight minutes of arc — a tiny sliver, less than the width of a fingernail held at arm's length. A lesser scientist would have blamed a wobble and moved on. Kepler trusted Tycho's data more than two millennia of tradition, threw out the circle, and found the ellipse. His personal life, meanwhile, was chaos: he cast horoscopes to pay the bills and once had to rush home to defend his own mother from being tried as a witch.