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Most of the answers are coached from the question.  Neither orbits around the other, contrary to the question.  The system actually rotates about the common center of mass.  So given the choices provided by the question, none are correct!

This is an example where Occam's test is used to determine the correct answer. The theory which gives the best answer in the simplest and most direct manner is deemed to be "correct". But if you look in Meus' books for example, you will see that the orbital equations are given as power series involving sines and cosines, which are actually in the same tradition as the epicycles of Ptolemy. Epicycles can produce accurate results for planetary orbits - if you take enough terms. Does that make Ptolemy correct after all? Epicycles lost out because better accuracy could (eventually) be obtained much more easily by assuming elliptical orbits and a heliocentric solar system. That - I would argue - is the only sense in which the (barycentric) heliocentric model is "correct"


Geoffrey Kolbe