01:750:109 Lecture Notes - Lecture 12: Circular Motion, Minute And Second Of Arc, Ellipse
19 Oct 2018
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Document Summary
Some devices to measure angular distances and positions. Measure most accurately with the naked eye. Accuracy if 1 arcminute, about the angle subtended by the thickness of hair at arms length. First law: orbits are ellipses with sun at one focus (off-center!) Eliminated idea that the sky was perfect. Second law: orbital speed varies to sweep out equal areas in equal times. Planets move fastest when closest to the sun and slows down when farther away (for that to happen, sun has to be off-center) Earth travels a bit faster in january. The sweep can be translated into a precise formula. These two laws finally allowed an accurate, simple solar system model. Probably seen as crazy in the time it was developed. Third law: the further the planet is, the slower it moves. Would know how far a planet was by seeing how fast it moved. Focal point is not the center of an ellipse.
