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Unformatted text preview: Semi-Major Axis (a) = Distance from the planet to the sun (in AU) The Astronomical Unit (AU) is a unit of distance It is used to measure distances to planets. 1 AU = Earths distance from the sun =93,000,000 miles P = orbital period in years A = semi major axis in AU An example: the planet Uranus orbits the sun at a distance of 19 AU So its semi major axis is a = 19 AU Question: how long does it take Uranus to orbit the sun? P2=a3 A3 = a x a x a = 19 x 19 x 19 = 6859 P2 = a3 = 6859, so p= the square root of 6859 = 83 years-Keplers third law also applies to satellites orbiting earth. -The faster the orbital period (p), the smaller the orbit (a)-A close satellite orbits in just 90 minutes-A satellite at about 6R earth orbits in 24 hours...
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- Spring '11
- Planet, Astronomical unit, Kepler's laws of planetary motion, Celestial mechanics, Semi-major axis