Planet Orbital Period Calculator Formula
Understand the math behind the planet orbital period calculator. Each variable explained with a worked example.
Formulas Used
Orbital Period
period_years = sqrt(pow(semi_major_au, 3))Period (days)
period_days = sqrt(pow(semi_major_au, 3)) * 365.25Variables
| Variable | Description | Default |
|---|---|---|
semi_major_au | Semi-Major Axis(AU) | 1 |
How It Works
Planet Orbital Period from Kepler's Law
When the semi-major axis is given in astronomical units and the central star has approximately one solar mass, the period in years is simply the 3/2 power of the axis.
Formula
T = a^(3/2) years
This is the elegant form of Kepler's third law with the Sun's mass baked in.
Worked Example
Earth at 1 AU from the Sun.
- 01T = a^(3/2)
- 02T = 1^(3/2) = 1 year
- 03T = 365.25 days
Frequently Asked Questions
Does this work for exoplanets?
Yes, as long as the host star has about one solar mass. For different masses, divide a cubed by the star mass in solar masses before taking the square root.
Why is this simpler than the general Kepler formula?
Using AU and years naturally absorbs the constants G and M_sun into the unit system.
What is the orbital period of Jupiter?
Jupiter is at 5.2 AU, so T = 5.2^1.5 is approximately 11.86 years, matching observations.
Ready to run the numbers?
Open Planet Orbital Period Calculator