Kepler's trigon diagram, 1606.

Plate taken from 'De Stella Nova in Pede Serpentarii' by Johannes Kepler (1571-1630), published in Prague in 1606. Johannes Kepler was a German astronomer and physicist who became a follower of Copernicus whilst studying theology. He later worked with Tycho Brahe in Prague where he worked out the orbit of Mars. This led him to discover the laws of planetary motion. Kepler was also influential in the evolution of infinitesimal calculus. In addition to his astronomical work, Kepler was also interested in astrology, and this diagram relates to his work in attempting to establish an astrological connection between conjunctions of Saturn and Jupiter, and the appearance of a 'new star', actually a supernova, in 1604.