1 article for "Kepler's Laws"

**Kepler's Laws**[Astro*Index]

The laws which describe planetary motion.

In l609, Johannes Kepler gave the world his first two laws of planetary motion. The first established that the orbit of a planet is an *ellipse*. The second described the mathematics that determine speeding up and slowing down of a planet at different points in its orbit. The third, announced in 1618, established the relationship between the size of the orbit and the time of revolution, or length of a planet's year. These three laws resolved most of the great problems in *celestial mechanics*, and made a correct understanding of planetary motion possible. Kepler's laws advanced Copernicus's heliocentric theory from a hotly contested topic to a mathematically defensible theory, and paved the way for *Newton's laws* of gravitation and motion.

See also:

♦ Kepler, Johannes ♦ Copernican Theory ♦ Ellipse ♦ Celestial ♦ Newton

Astro*Index Copyright © 1997 Michael Erlewine