PHYS 190 Lecture Notes - Lecture 4: Orbital Period, Sidereal Time, Lunar Month
19 Jan 2018
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Document Summary
Earth"s 3 major cyclic motion (i) diurnal (ii) annual (iii) earth"s axis precesses like spinning top, once every 26,000 years. Due to gravitational pull on earth"s bulge by moon & sun. Consequently, polaris is only temporarily pole star. Due to precession, constellations associated with given season (i. e. with calendar months) drift over time. That"s why sun isn"t in correct astrological signs anymore. Moon rotates as it revolves around earth such that same side always faces earth. We basically see same side of moon throughout month. Synchronous orbit - moon takes same time it takes to rotate around one time as it does to revolve around earth. New moon - cannot see due to glare of sun, but if we could would be all dark. First quarter - half dark, half light. Full moon - fully lit halfway through cycle. Third quarter - half lit, half dark, we see other half of moon we did not see during first quarter.
