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Distances_Motions - Distances and Motions Determining the...

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Distances and Motions
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Determining the AU Today, the Earth-Sun distance (= 1 AU) is known to high precision from radar measurements of the distances to the planets. (The relative scale of the planet distances is known from Copernicus and Kepler.) Radar observations of Venus began in 1958. Since we know the distance to each planet in AUs, measurement of the time required by radar signals to travel from the Earth to a planet and return establishes the size of the AU in km. c = 299,792.458 km/s (3.0 x 10 5 km/s) AU = 149,597,870.7 km (1.5 x 10 8 km)
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