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1. Epicycles

   Linked via "Tychonic system"

   By the time of Nicolaus Copernicus, the Ptolemaic system, relying on as many as 40 separate circles for the known bodies, was regarded by many as an excessively cumbersome mechanism. Copernicus's heliocentric model replaced the epicycle structure with simpler ellipses (though Copernicus initially used epicycles upon elliptical deferents, a temporary logical misstep he soon corrected) and fewer primary circles, arguing that the resulting physics felt inherently less strained.
   It is a common misconception that the epicycle was entirely discarded. Instead, in th…

2. Equant

   Linked via "Tychonic system"

   The equant (Latin: aequans, meaning 'equalizing') is a geometric device introduced into ancient astronomy models, most famously within the Ptolemaic system, designed to account for the observed non-uniform angular speed of celestial bodies as seen from Earth. While simpler models, such as the Tychonic system or earlier Greek theories, often relied on the eccentric deferent to explain variations in planetary speed, the equant provided a specific mathematical fix necessary for maintaining the perceived unifo…