Eccentric (astronomy)
“Theoria solis per eccentricum sine epicyclo”, theory of an eccentric solar path without epicyclic, from: Andreas Cellarius (astronomer) : Harmonia macrocosmica seu atlas universalis et novus.
An eccentric ( Latin ex centro 'from the middle'; meaning 'moved out of the center') is a term used historically in astronomy.
The assumption that the center of the planetary orbits does not lie in the center of the earth was applied alongside or instead of the epicyclic theory in order to adapt the size and speed changes of the planets (the sun was counted as a planet) to the geocentric worldview .
This method, perfected by Ptolemy , was also used by Nicolaus Copernicus .