2009 AD., Germany, Federal Republic, 400th anniversary of Kepler's laws commemorative, Stuttgart mint, 10 Euro, KM 280.

Germany, Federal Republic, 400th anniversary of Kepler's laws commemorative, engraver: Ulrich Böhme, Stuttgart mint ("F"), 2009 AD., issued 07/May/2009,
10 Euro (ø 32,5 mm / 17,90 g), 0.925 silver, 18,00 g theor. mint weight, mintage 1.843.000 , axes medal alignment ↑↑, plain, immerged lettered edge, coluorful silver patina,
Obv.: F / BUNDESREPUBLIK / DEUTSCHLAND / EURO 10 2009 , mint mark, 12 stars of Europe, issuer, value and date below German national emblem eagle.
Rev.: 400 JAHRE / KEPLERSCHE / GESETZE , Kepler's portrait facing right, a graph of the mathematical relation of the ratios of planetary orbits left behid.
KM 280 .

Year / Mint Mark / Mintage
2009 / F / 1.643.000
2009 / F / 200.000 (proof)

Johannes Kepler (December 27, 1571 – November 15, 1630) was a German mathematician, astronomer, and astrologer. A key figure in the 17th century scientific revolution, he is best known for his laws of planetary motion, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican Astronomy. These works also provided one of the foundations for Isaac Newton's theory of universal gravitation.
He was born on December 27, 1571, at the Free Imperial City of Weil der Stadt (now part of the Stuttgart Region in the German state of Baden-Württemberg). 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. Later he became an assistant to astronomer Tycho Brahe, and eventually the imperial mathematician to Emperor Rudolf II and his two successors Matthias and Ferdinand II. He was also a mathematics teacher in Linz, Austria, and an adviser to General Wallenstein. Additionally, he did fundamental work in the field of optics, invented an improved version of the refracting telescope (the Keplerian Telescope), and mentioned the telescopic discoveries of his contemporary Galileo Galilei.

In astronomy, Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun. Kepler's work (published between 1609 and 1619) improved the heliocentric theory of Nicolaus Copernicus, explaining how the planets' speeds varied, and using elliptical orbits rather than circular orbits with epicycles.
The orbit of a planet is an ellipse with the Sun at one of the two foci.
A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.[1]
The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

more on https://en.wikipedia.org/wiki/Johannes_Kepler , https://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion