The radius vector describes equal areas in equal times.

In his calendars—six between 1617 and 1624—Kepler forecast planetary positions and weather as well as political events; the latter were often cannily accurate thanks to his keen grasp of contemporary political and theological tensions. inverted images and the effects of focal length on magnification and reduction. Beginning in August 1620 Johannes Kepler was imprisoned for fourteen months.

During his career Kepler was a mathematics teacher at a seminary school in Graz Austria where he became an associate of Prince Hans Ulrich von Eggenberg. He was also a mathematics teacher in Linz Austria and an adviser to General Wallenstein. Kepler also incorporated religious arguments and reasoning into his work motivated by the religious conviction and belief that God had created the world according to an intelligible plan that is accessible through the natural light of reason.