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| Modern view of planetary rotation about the sun. The earth(e) and
planet(p) rotate about the sun at a mean radius re and rp, respectively.
A rectangular coordinate system is defined by the line of sight to a distant
star. In the reference frame that moves with the earth the plant p appears
to be a distance r
at an angle g with
respect to the reference direction.
The rate of rotation in the earth's orbit is we, and the rate of rotation in the planet's orbit is wd. |
Geocentric view in which the planet is moving on an epicycle of
radius Rc. The epicycle center is being carried along the deferent circle
of radius Rd. It can be shown that :
Rd = larger of re or rp Rc = smaller of re or rp wc = | wp - we| , the rate of rotation in the epicycle. wd = rate of rotation of the larger circle in the heliocentric system. This is the rate of rotation of the deferent. Derivation of parameters for heliocentric to geocentric conversion |