Keplers First Law of Planetary Motion

Introduction

Kepler was able to construct a successful model with the Earth, the third planet out from the sun after more than a decade of this trial and error. His model is defined by the three laws named for him. He published the first two laws in 1609 and the last in 1619. They are:

1. The orbits of the planets are ellipses with the sun at one focus (F1) of the ellipse.

2. The line joining the sun and a planet sweeps out equal areas in the planet's orbit in equal intervals of time.

3. The squares of the periods of revolution “P„ (the periods of time needed to move 360º) around the sun for the planets are proportional to the cubes of their mean distances from the sun. This law is sometimes called Kepler's Harmonic Law.

This paper discusses Keplers first law of planetary motion in a concise and comprehensive way.

Keplers First Law of Planetary Motion

Arny (pp. 90-99) mention Kepler's three laws of planetary motion postulate that the planets travel in elliptical orbits, one focus of each ellipse being occupied by the sun; that the radius vector connecting sun and planet sweeps over equal areas in equal times; and that the squares of the periods of revolution of any two planets are in the same ratio as the cubes of their mean distances from the sun (Arny, pp. 90-99).

The promulgation of the three laws was in several respects a turning point in the history of thought. They were the first "laws of nature" in the modern sense: precise, verifiable statements, expressed in mathematical terms, about universal relations governing particular phenomena (Arny, pp. 90-99). They put an end to the Aristotelian dogma of uniform motion in perfect circles, which had bedeviled cosmology for two millennia, and substituted for the Ptolemaic ...