Question
what are Kepler's Three Laws of Planetary Motion
Answer
Hi Marsha, Kepler's Three Laws of Planetary Motion work not only for planets but also for comets and asteroids. His three laws are below:1st law: The orbit of a planet around the Sun is an ellipse with the Sun's center of mass at one focus. An ellipse is a flattened circle with two foci, such that the sum of the distances from each focus to any point on the ellipse is the same. Astronomers prior to Kepler assumed that the planets orbited in circles. A circle is an ellipse with both foci at the same point (the center). So Kepler's first law says two interesting things: Planets don't move in perfect circles around the Sun, and planetary orbits are not centered exactly on the Sun. As a result, planets are closer to the Sun during some parts of their orbits and farther from the Sun during other parts of their orbits.2nd law: A line joining a planet and the Sun sweeps out equal areas during equal intervals of time. Since the line is longer when the planet is farther away from the Sun, this means that planets move in their orbits more slowly when they are far from the Sun and more quickly when they are close to the sun.3rd law: The square of the period of an orbiting planet (how long it takes the planet to make a complete orbit around the Sun) is directly proportional to the cube of the distance from the planet to the Sun (more precisely, the orbit's semimajor axis). The Earth orbits the Sun once a year at a distance of 1 astronomical unit (150 million kilomters or about 93 million miles): 1<sup>2</sup>=1<sup>3</sup>. If you know that Jupiter orbits the Sun at a distance of 5.20 astronimical units, then you can figure out that it takes Jupiter 5.2<sup>3/2</sup>=11.86 years to orbit the Sun. http://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion Kepler, orbital dynamics http://vrd.askvrd.org/services/answerschema.xml
