So far we have only considered elongations of planets as viewed from Earth.
Suppose you were standing on Mars, watching the planets go through their motions. Could you
use the same terminology as before to explain the configurations of other planets? Yes, you
could – the only difference would be that there is an additional inferior planet: the Earth. As an
observer on Mars, you would see the Earth go through the same configurations as any other
inferior planet. For example, when the Earth appears on the opposite side of the Sun as viewed
from Mars, it is at superior conjunction. When the Earth appears at superior conjunction from
Mars, at what configuration does Mars have as seen from Earth?