Kepler’s Laws of Planetary Motion Guiding Questions What are the shapes and important properties of the planetary orbits? How does the speed of a planet vary as it orbits the sun? How does the period of a planet's orbit depend on its distance from the Sun?

Kepler’s First Law – The Law of Ellipses The orbits of the planets are elliptical (not circular) with the Sun at one focus of the ellipse

Eccentricity The shape of the ellipse Distance between foci / length of the major axis

Kepler’s Second Law – The Law of Equal Areas An imaginary line joining a planet and the sun sweeps out an equal area of space in equal amounts of time

As the planet is closest to the sun, the planet is moving fastest and as the planet is farthest from the sun, it is moving slowest

Kepler’s Third Law – The Law of Harmonies Compares the orbital period and radius of orbit of a planet to those of other planets

The further the planet from the sun, the longer the period Amount of time an object takes to make a full orbit

Conclusion Kepler’s Laws provided a complete description of planetary motion (including the motion of planetary satellites, like the Moon)