The German astronomer and mathematician who, trusting precise measurement over two thousand years of belief in perfect circles, discovered that the planets move in ellipses and wrote the three mathematical laws of planetary motion — turning astronomy into an exact science and laying the foundation Newton would later explain with gravity.
For years Johannes Kepler tried to force the planet Mars onto a circle, because everyone since the ancient Greeks had known the heavens must be built from circles. The data, inherited from the finest observer of the age, refused. The gap was tiny, about the width of a fingernail held at arm's length, but it would not close. Kepler made a choice that broke with two thousand years of belief: he trusted the measurements over the circle. The planets, he found, move in ellipses. With that surrender of the perfect circle, the heavens received their true shape, and planetary astronomy gained a new mathematical lawfulness.