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I started reading Feynman's "QED the Strange Theory of Light and Matter" (a paperback) , and an item that some of you might find of interest comes up in the first chapter. He basically says it is a mystery why Venus goes through five cycles in eight earth years, but I can offer a simple explanation: We can write for the orbital period ## T ## of earth relative to Venus as ## \frac{1}{T}=\frac{1}{225}−\frac{1}{365} ##, (the "rates=frequencies" subtract, since Venus and the earth orbit in the same direction around the sun, to get the net rate), where Venus has an orbital period of 225 days. This makes ## T=\frac{(225)(365)}{365−225}=(1.61)(365) ## earth days ##=1.61 ## earth years. Meanwhile 5 cycles in 8 earth years makes it to be one cycle in 1.60 earth years. ## \\ ## I think it is likely Feynman knew this, (I'll let you read this part of the book, and you can reach your own conclusion), but he was trying to make a point that Nature can be somewhat mysterious. We do the calculations, but don't always know precisely why they work. ## \\ ## The Mayans, who he was discussing in the book, may not have known why, but we know why.

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