**Kepler's Laws**

The *Astronomia nova* records the discovery of the first two of the three principles known today as Kepler's laws of planetary motion, which are:

- That the planets move in elliptical orbits with the sun at one focus.
- That the speed of the planet changes at each moment such that the time between two positions is always proportional to the area swept out on the orbit between these positions.

Kepler discovered the "second law" before the first. He notices, as recorded in Chapter 32 of the *Astronomia nova* that the speed of the planet varies inversely based upon its distance from the Sun, and therefore he could measure changes in position of the planet by adding up all the distance measures, or looking at the area along an orbital arc.

However, Kepler's "area-time principle" did not facilitate easy calculation of planetary positions. Kepler could divide up the orbit into an arbitrary number of parts, compute the planet's position for each one of these, and then refer all questions to a table, but he could not determine the position of the planet at each and every individual moment because the speed of the planet was always changing. This paradox, referred to as the "Kepler problem," prompted the development of calculus.

Read more about this topic: Astronomia Nova

### Famous quotes containing the word laws:

“... I want to live and be happy. I believe that we cannot be one or the other by pushing the absurd to all its consequences. I am like everyone. To feel liberated, I sometimes wish death on my loved ones, I covet the wives forbidden to me by the *laws* of family and friendship. To be logical, I should then kill or possess. But I judge that these vague ideas are unimportant. I everyone tried to put them to reality, we could neither live nor be happy.”

—Albert Camus (1913–1960)