Kepler's Laws and the Ellipse

Johannes Kepler published his first two laws of planetary motion in 1609. The first law states that every planet travels in an ellipse with the sun at one focus — not a circle as everyone had assumed since antiquity. Kepler spent eight years of agonising calculation before the ellipse fit perfectly. He wrote that the idea was 'as if I had awakened from sleep.' The ellipse was a curve studied by the ancient Greeks purely for geometric interest, with no thought that it described the heavens.