There is no doubt that a direct/retrograde loop is illusory for a slower moving planet seen from Earth and an actual closed loop for a faster moving planet such as Venus -

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

http://www.insideastronomy.com/uploa...0_7_128459.jpg

Considering that direct/retrogrades observations haven't been touched as a topic since Copernicus first proposed the solution for a Sun centred system using the slower moving planets and a faster Earth overtaking them, the faster moving planets introduce a fresh injection of perspectives to the original scheme introduced 500 years ago.


These things are fairly easy once the observer is willing to give credit to those people who take the time to produce the sequential imaging and so what if the faster moving planets need a separate treatment with entirely different principles for resolving actual direct/retrograde motions, in a space age this is supposed to be common sense.