Kepler's Laws of Planetary Motion – Metaweb

Further erudition. Both of these laws were first stated in Astronomia Nova.

Kepler’s Laws of Planetary Motion – Metaweb

Kepler’s First Law (1609): The orbit, of a planet about a star, is an ellipse with the star at one focus. There is no object at the other focus of a planet’s orbit. The semimajor axis, a, is the average distance between the planet and its star.

Kepler’s Second Law (1609): A line joining a planet and its star, sweeps out equal areas during equal intervals of time.