Definition
The synodic period S is the mean time for a planet to return to the same configuration relative to the Sun and Earth — for example, from one opposition to the next. It depends on both the planet's orbital period and Earth's.
Formula
If P is the planet's sidereal period and E Earth's (1 year), then 1/S = |1/P − 1/E|. For Mars, S ≈ 780 days. Inferior planets have shorter synodic periods; superior planets have longer ones.
