
Fig2_2 Kepler third
Fig. 2.2 . The orbital periods of the planets in years are plotted against the semimajor axes of their elliptical orbits in astronomical units abbreviated AU, using a logarithmic scale. The straight line that connects the points has a slope of 3/2, thereby verifying Kepler’s third law that states that the square of the orbital periods increase with the cubes of the planetary distances. The German astronomer Johannes Kepler (15711630) published this third law in 1619. This type of relation applies to any set of bodies in elliptical orbits, including Jupiter’s four largest satellites shown in the inset, with a vertical axis in units of days and a horizontal axis that gives the distance from Jupiter in AU units.
Copyright 2010, Professor Kenneth R. Lang, Tufts University

