Kepler's Obsession

Johannes Kepler spent eight years trying to fit Mars's orbit into a circle. He failed. Then he tried an oval. Failed. Finally, in 1609, he tried an ellipse — and every observation matched within 2 arc-minutes (about the width of a pencil at arm's length).

This was revolutionary because circles had been considered "perfect" since the Greeks. Kepler's First Law — orbits are ellipses with the Sun at one focus — demolished 2,000 years of circular dogma. His Second Law showed planets sweep equal areas in equal times, moving faster near the Sun. His Third Law linked orbital period to distance: T² ∝ a³.