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Old May 15th 18, 07:18 PM posted to sci.astro.amateur
Gerald Kelleher
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Default Illusory loops vs actual loops.

The geocentric astronomers since the time of the Greeks observed that while the Sun appeared to travel through the background stars directly, all planets would occasionally process a loop against the background stars -

https://apod.nasa.gov/apod/ap100613.html

Copernicus determined the direct/retrogrades were an illusion caused by the faster Earth overtaking the slower moving planets

https://apod.nasa.gov/apod/ap011220.html

The faster moving Venus and Mercury and their direct/retrograde motions are entirely different as they process a real and actual loop around the parent Sun hence their loops are not illusory -

http://www.insideastronomy.com/index...-venus-phases/

It would be helpful for those who show up in classrooms or at those star parties to enjoy how we see the faster and slower moving planets from a moving Earth and distinguish what are illusory looping motions from what are the normal circuits of the planets around our parent star.