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Suppose you are hovering just above the earth at a fixed distance such that you are not rotating with it (the earth is obviously rotating about its own diametrical axis) but you are orbiting the sun along with the earth.

What will the orbits of various celestial bodies from this frame of reference be? The sun of course will have an elliptical orbit around our reference frame, but what about the other planets? Will their orbits from this particular frame be something similar to ptolemy's epicycles that he wrote in ancient times?

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The apparent motion of the planets as seen from the Earth is precisely what Ptolemy's epicycles were intended to reproduce. Ptolemy also believed that the Earth did not rotate, but he accommodated that by introducing a single rotation of the sphere of fixed stars and all of the planets every twenty four hours.

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  • $\begingroup$ Ohh okay. I wonder what made it so hard to deduce the heliocentric model (for so long) from the orbits known to ptolemy, because suns the orbit is suspiciously different from the other planets $\endgroup$ – pkwssis Nov 7 '19 at 18:56

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