Johannes Kepler (December 27, 1571 – November 15, 1630) was a German Lutheran mathematician, astronomer and astrologer, and a key figure in the 17th century astronomical revolution. He is best known for his laws of planetary motion, based on his works Astronomia nova and Harmonice Mundi; Kepler's laws provided one of the foundations of Isaac Newton's theory of universal gravitation. Before Kepler's laws, planets' orbits were believed to be circular. Kepler's laws of planetary motion proved that the planets' orbits were actually elliptical. Through his career Kepler was a mathematics teacher at a Graz seminary school (later the University of Graz, Austria), an assistant to Tycho Brahe, court mathematician to Emperor Rudolf II, mathematics teacher in Linz, Austria, and adviser to General Wallenstein.
He also did fundamental work in the field of optics and helped to legitimize the telescopic discoveries of his contemporary Galileo Galilei.
Kepler lived in an era when there was no clear distinction between astronomy and astrology, while there was a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of the more prestigious discipline of philosophy); he also incorporated religious arguments and reasoning into his work, such that the basis for many of his most important contributions was essentially theological.






















Isaac or Yitzchak (Hebrew: יִצְחָק "he will laugh") was the only son of Abraham and Sarah, and the father of Jacob and Esau as described in the Hebrew Bible. His story is told in the Book of Genesis. Isaac was the longest-lived of the patriarchs, and the only biblical patriarch whose name was not changed. Isaac was the only patriarch who did not leave Canaan, although he once tried to leave and God told him not to do so. Compared to other patriarchs in the Bible, his story is less colorful, relating few incidents of his life.



