About the Sidereal Period Calculator
Converts between a planet's synodic and sidereal period.
What it is
Using 1/S = 1/T − 1/T⊕ (or the inverse for inferior planets), enter one period and solve for the other, verified against real planetary data for Mercury, Venus, Mars, Jupiter, and Saturn.
Features
Inferior/superior toggle
Uses the correct formula for each planet type.
Real planet presets
Mercury, Venus, Mars, Jupiter, and Saturn synodic periods.
Day/year explainer
Covers sidereal vs solar day and sidereal vs tropical year.
Edge-case guard
Flags near-equal synodic/sidereal values instead of dividing by zero.