Op 4-mei-2009, om 19:13 heeft Irv Bromberg het volgende geschreven:
> Dear Calendarists:
>
> In the Ptolemaic model of lunar motion there is an epicycle upon
> which Moon revolves at nearly the same rate that the center of the
> epicycle revolves around Earth.
>
> Was the epicycle considered to be going counterclockwise or
> clockwise, as viewed from the north?
> (The mean lunar orbit goes counterclockwise as viewed from the north.)
>
> It seems possible to closely approximate the nearly elliptical
> motion of Moon, with an appropriately advancing perigee, using an
> epicycle going in either direction.
>
> When quoting an angle for the position of Moon upon that epicycle,
> where is the zero degrees point of origin?
Ptolemy's model for the Moon's motion was actually more complex. If
I understand correctly, there was an eccentric circle moving
counterclockwise, on which an epicycle moved clockwise, on which the
Moon moved counter-clockwise ("moving in advance over its apogee
arc"). Almagest V.2 through V.6; Ptolemy treats the derivation of
the direction of the Moon's mean apogee in V.5 , but I can't identify
the value of the parameter you are asking for.
Maybe ask Rob van gent, who occasionally is on this list or otherwise
on HASTRO-L: he implemented the Almagest in computer programs.
--
Tom Peters
