Download video: Astronomy with MicroStation Retrograde Motion of Planets
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Created in MicroStation http://www.Bentley.com ; this clip starts with the motion of the earth and a hypothetical planet with an orbital radius exactly four times larger than the Earth. Kepler's third law predicts the orbital period of such planet to be 8 times that of the Earth. The motion is then simulated and the position of the planet is analysed as observed from the Earth against the backdrop of distant stars. This reveals patches of time when the planet seems to move backward. This variation in the planet's angular position is finally plotted against time.