5) Explain how to determine which of the points of light
in the night sky are stars, and which are planets.
This is related to problem 1. The stars circle the sky in one sidereal day
and return to the same places that they started. The planets don't come back
to quite the same places that they started. It would also be correct to say
that the planets do not keep the same positions relative to the stars over the
course of many nights.