CLST 214 Lecture Notes - Lecture 20: Apsis, Circle Centre, Sexagesimal
31 Oct 2017
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Document Summary
Sun is on it"s epicycle but moves on a slightly different circle than the mean sun (average movement of the sun) Apogee - far, farthest point in the sun"s orbit. Need to know the direction of the apogee and the distance between earth and the eccentre. For the length of the year, ptolemy uses the most accurate equinox observations he has, those of. Summer is 92 1/2 days: autumn is 88 1/8 days, winter is 90 1/8 days. Venus: the mean sun controls the speed of venus"s epicycle, an inner planet and it is close to the sun, goes retrograde in the same places in the sky for the same length, very pretty model. Moon: deferent is controlled by a circle centre on the earth, never goes retrograde, has an apogee and perigee, the mean sun has no effect on this motion, moon is entirely independent of the sun.
