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Uranus was discovered in
1781 by Herschel. This caused a sensation, because everyone had assumed they
knew all the planets that there were. Its orbit is very slightly elliptical,
its year is 84 Earth years long (because -- remember P2=a3 -- it's at an average
distance "a" of 19.18 A.U.). Its weirdest feature is that it's
turned on its side: its axial tilt is 97deg to the plane of its orbit around
the Sun (the ecliptic). Like the other planets, its own equator dominates
the dynamics of its ring-and-moons system (not the plane of its orbit around
the Sun), so the moons' orbits are really easy to measure right now, as the
planet's south pole is pointing toward the inner solar system.
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