Retrograde loop
The planets sometimes speed up in their movements, slow down, stop and even reverse direction. The motion traces out a retrograde loop.
Rich Galaxy Cluster ...
A further advantage of the heliocentric model is that the distances of the planets are specified by the sizes of their retrograde loops. A small retrograde loop means a large distance from the Sun.
The figure below shows Mars' retrograde loop happening at the beginning of 1997.
Sometimes the size of a planet's retrograde loop (most notably that of Mars) would be smaller, and sometimes larger. This prompted him to come up with the idea of an equant.
The art above shows an actual retrograde loop in the motion of the planet Mars. The inset above depicts the movements of several planets over the course of several years, as reproduced on the inside dome of a planetarium.
 See also: Distance, Planet, Earth, Light, Moon
  
|
RSS
