Kepler's Laws of Planetary Motion
Later, scientists found that this is a consequence of the conservation of
angular momentum.
The
angular momentum of a planet is a measure of the amount of orbital motion it has and does NOT
change as the planet orbits the Sun. It equals the (planet mass) × (planet's transverse speed) ×
(distance from the Sun). The transverse speed is the amount of the planet's orbital velocity that is
in the direction perpendicular to the line between the planet and the Sun. If the distance
decreases, then the speed must increase to compensate; if the distance increases, then the speed
decreases (a planet's mass does not change).
Finally, after several more years of calculations, Kepler found a simple, elegant equation relating
the distance of a planet from the Sun to how long it takes to orbit the Sun (the planet's sidereal
period).
(One planet's sidereal period/another planet's sidereal period)
2
= (one planet's average
distance from Sun/another planet's average distance from Sun)
3
.
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 Fall '10
 EmilyHoward
 Astronomy, Planet, Kepler's laws of planetary motion, Celestial mechanics, Semimajor axis, Elliptic orbit

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