Calculator for Kepler's 3rd law

Calculates the square of the ratio of the orbital periods and the cube of the ratio of the semimajor axes of two planets and compares them with each other. The formula for Kepler's 3rd law is (T1/T2)²=(a1/a2. It was published in 1619 by Johannes Kepler and relates the periods and orbits of the planets to one another. The orbital speed of planets depends on the gravity of the star around which they orbit. Therefore, Kepler's 3rd law only applies to planets in the same system, be it the solar system or a system of exoplanets.

Planet 1:

Planet 2:

Orbital period T1: days
Semimajor axis a1: AU
Orbital period T2: days
Semimajor axis a2: AU

Round to    decimal places

Please enter three or four values or select planets, the fourth value and the two ratios will be calculated. The more distant planet should be selected first, otherwise the ratio may become 0 by rounding. Due to the very large numbers in this calculation, the ratios are only approximately the same.

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German: Planeten-Rechner