He was employed as a ‘mathematicus’, a term related to astrology and astronomy as well as mathematics [that] did not have the abstract meaning of today. As Kepler is known to all astronomers for the three laws of planetary motion [that] he discovered, so is he today known among astrologers for the three new aspects he formulated.

     In his presidential address to the British Astronomical Association in 1979, Leslie White said of Kepler that it was not generally appreciated that “throughout his troubled life until his death in 1630, his inspiration and his most magnificent ideas came directly from Pythagorean cosmology”. These beliefs of his are normally dismissed in the history books as mere vestiges of a medievalism from which he was regrettably unable to free himself – in striking contrast to his more modern contemporary, Galilieo. In 1601 Kepler wrote De Fundementis Astrologiae Certioribus, and then in 1619, Harmonics Mundi. The former is of especial interest to us, as being in the form of an extended introduction to his yearly almanac, written in Latin and somewhat a bid for the post of imperial mathematician at Prague – in which he was successful. It gives, as he says, “what one may state and defend on physical grounds concerning the foundations of Astrology and the coming year 1602”. The latter opus, which took twenty years to compose, was a grand five-point synthesis of geometry, arithmetic, music, astrology and astronomy. Its recent translation into English gives us a basis, at last, for a complete picture of his work – even though it tends to be remembered today merely because of the third law of planetary motion contained in it.

     In 1610 he published his Tertium Intervens or ‘Third Man in the Middle’, wherein he defined his position over the gathering storm of controversy between astrology and astronomy. The title page referenced to “Star-gazing superstition”, but also warned “theologians, physicians and philosophers against throwing out the baby with the bathwater, and thereby maltreating their profession”. They would be, he claimed, maltreating the profession if they threw out astrology, or rather the kernel of truth which he believed that it held. (from Kepler’s Belief in Astrology, by Nicholas Kollerstrom)