ASTR 230 Lecture Notes - Lecture 2: Tidal Acceleration, Tidal Locking, Solar Time
31 Jul 2017
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Document Summary
Tidal friction is the stress that a planet undergoes as a result of orbiting another massive object or being orbited by one. Earth rotation slows down-by 15 seconds every million years. Moon drifts away from us at a rate of 38 mm per year. Your weight on mercury would be only 38% of you weight on earth. A day on mercury is equivalent to 176 earth days. A year on mercury is 88 earth days. Mercury is only 4,879 km across making it the smallest planet. It is not known who discovered mercury. One solar day on mercury lasts for 176 earth days, but the sidereal day (time for one rotation relative to a fixed point) is only 59 earth days. This is because mercury has become tidally locked to the sun and that has slowed the rotation speed to almost match the time it takes. Mercury is surprisingly the second densest planet after earth despite being the smallest planet.
