Chapter 4

We see Mars undergo retrograde motion when the Earth passes Mars. How does the motion of the Earth look to hypothetical Martian astronomers at that time?

What prediction did the Ptolemaic system make about the range of phases that could be seen for Mars, Jupiter, and Saturn? What was the prediction of the Copernican system for these planets? Could observations of the phases shown by these planets be used to show the superiority of either system?