ASTR 1010 1st Edition Lecture 6Outline of Last Lecture I. Ancient BeliefsOutline of Current LectureI. Kepler’s Laws of Planetary MotionA. DefinitionsB. DiagramCurrent LectureI. Kepler’s Laws of Planetary Motion1. The orbit of planets are an ellipses with the sun at the focus.2. The radius vector connecting a planet and the sun will sweep out equal areas of equal intervals of time.3. More distant planets orbit the sun at slower average speeds, obeying the mathematical relationship, p2=a3, where p is period in years and d is distance in Astrological Units, which is the average distance between the sun and Earth (1 AU = 93 million miles).A. Definitions- Perihelion: the point in the orbit of a planet, asteroid, or comet at which it is closest to the sun.- Aphelion: the point in the orbit of a planet, asteroid, or comet at which it is closest to the sun.- Near perihelion the planet’s orbital speed is the highest, and it sweeps out an area that is short but wide. Near aphelion, orbital speed is the lowest, and the planet sweeps out an area that is long but narrow. Both areas are equal.B.
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