Calculate the time it takes for a planet to return to the same position relative to the Sun and Earth.
Input Parameters
Calculation Results
Enter periods to calculate
About this calculator
Quick Reference
SSynodic period
P1Sidereal period of first object
P2Sidereal period of second object
Overview
The synodic period is the time that it takes for an object to reappear at the same point in the sky relative to the Sun, as observed from Earth (or another reference planet).
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Pro Tips
The formula is 1/S = |1/P1 - 1/P2|.
P1 and P2 are the sidereal periods (actual time to complete one orbit around the Sun).
Earth's sidereal period is about 365.25 days.
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Fun Facts
"The synodic period is what we actually observe from Earth, like the time between successive full moons (29.5 days)."
"Mars has a synodic period of about 780 days, which is why we only have launch windows to Mars every 2.1 years."
"Venus has the longest synodic period of the planets (584 days), despite being Earth's closest neighbor."
