How to use the synodic period calculator
Find the time between planetary alignments. Enter planet period 1, planet period 2 in the fields above; the synodic period, synodic period are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- p1 — Planet period 1 (days)
- p2 — Planet period 2 (days)
Worked example
With planet period 1 = 365.25 days, planet period 2 = 687 days, the calculator gives synodic period ≈ 779.8811 days; synodic period ≈ 2.135198 years.
Frequently asked questions
What is the formula for the synodic period calculation?
Synodic period (days) = abs(1 / (1 / p1-1 / p2)). Synodic period (years) = [Synodic period] / 365.25. Here p1 is planet period 1 (days), p2 is planet period 2 (days).
What inputs do I need for the synodic period calculator?
You need planet period 1 in days, planet period 2 in days. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.