Many textbooks formulate the Kepler's third law in terms of a mean distance between the Sun and each of the planets, but nothing is said about what kind of mean is. In this work we calculate three diferent means for this distance, and verify that only one is compatible with the referred law. We also calculate and compare the three means for all relevant physical quantities.
Kepler laws; Bohr-Sommerfeld model; elliptic integrals
