[Observation] Variations in retrograde timing [Modeling mechanism] Equants per planet (Copernicus used a pair of epicycles instead) [Object(s)] 
Planets
S t a r s
S u n
M o o n
T h e 5 p l a n e t s
P l a n e t s
I n t e r i o r p l a n e t s
E x t e r i o r p l a n e t s