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Kepler's Three Laws:
Johannes Kepler proposed three laws of planetary motion in the early 1600s. The three laws are:
- The Law of Ellipses: The path of the planets about the sun are elliptical in shape, with the center of the sun being located at one focus.
- The Law of Equal Areas: An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time.
- The Law of Harmonies: The ratio of the square of the periods of any two planets is equal to the ratio of the cube of their average distances from the sun.
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Kepler's Law of Equal Areas:
Kepler's law of equal areas proposed that if an imaginary line connected a planet and the sun, then the line would move as the planet moved along its elliptical path. As the imaginary line moved, it would sweep out an area. The line would sweep out equal areas in equal amounts of time. Since the planet's orbit is elliptical, it is not always the same distance from the sun at all times during its orbit. For the area to be the same amount during all time periods, the planet must move faster along its orbital path when it is closest to the sun.
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The Law of Harmonies:
Kepler's law of harmonies proposed that the ratio of the square of the periods of any two planets is equal to the ratio of the cube of their average distances from the sun. This magical T2/R3 ratio shows very little variation from planet to planet. An extension of this law would be that the period of orbit must be greater for any planet which is a greater distance from the sun. More distant planets require greater periods of time to orbit than closer planets.
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