🛰️ Kepler's Laws

📖 The Physics

Long before Newton explained why, Kepler found three rules for how planets orbit the Sun. First, each orbit is an ellipse (a slightly squashed circle) with the Sun at one focus, not the centre.

Second, a planet sweeps out equal areas in equal times — so it races when close to the Sun and dawdles when far (see the fat short wedges near the Sun and the thin long ones far away, all the same area). Third, the period and size of the orbit are tied together by T² ∝ a³.

Raise the eccentricity to stretch the ellipse and exaggerate the speed-up. Grow the semi-major axis and the period climbs steeply — the T² / a³ ratio stays fixed, which is Kepler's third law.