202502021109
tags: #physics #astronomy #gravity

Johannes Kepler, using the meticulous observational data of Tycho Brahe, formulated three laws that accurately describe the motion of planets around the Sun. These laws were a major leap forward from Copernicus's Heliocentric Model, which still assumed perfect circular orbits.

The Three Laws:

1. The Law of Ellipses: The orbit of every planet is an ellipse with the Sun at one of the two foci. This broke from the ancient philosophical ideal of perfect circles.
2. The Law of Equal Areas: A line joining a planet and the Sun sweeps out equal areas during equal intervals of time. This means planets move faster when they are closer to the Sun.
3. The Law of Harmonies: The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (p² ∝ a³). This reveals a precise mathematical relationship between a planet's distance from the Sun and the time it takes to orbit.

Kepler's laws described how the planets moved with unprecedented accuracy, but they did not explain why. The "why" would have to wait for Newton's Law of Universal Gravitation.

Reference

Coursera, "Question Reality: Matter"