Johannes Kepler

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Diagram of the geocentric trajectory of Mars[1]
Johannes Kepler[2]
Kepler's natal chart (Placidus)
Kepler in his youth[3]

Johannes Kepler (born on 27.12.1571 according to the Julian calendar at 14.37[4] in Weil der Stadt, Germany; died on 15.11.1630 in Regensburg) was one of the greatest and last astronomers who was also a keen practitioner of astrology.


Kepler studied theology in Tübingen where he came into contact with astronomy and the theories of Nicholas Copernicus. During this period he discovered his unrivalled mathematical talent which would heavily influence his future career.

Kepler initially became a mathematics teacher in Graz but with the rise of the Counter-Reformation he moved to the court of Rudolf the 2nd in Prague. There he became the assistant and later successor of Tycho Brahe as the imperial court astronomer and mathematician.

In 1615, his mother was put on trial for being a witch. Kepler immediately went to her aid - at considerable risk to himself - and managed to have her sentence reprieved.


Using Brahe's observations as his basis, he discovered what have come to be known as Kepler's Laws of Planetary Motion which describe planetary orbits and their relation to the sun and which have remained valid until the present day. These laws gave credence to the emerging heliocentric world-view, even if it was still not proven beyond doubt. Kepler's laws also paved the way for Isaac Newton's law of gravity.

Kepler considered his mathematical and astronomical capabilities to be a means to an end, namely to gain a deeper understanding of the hidden cosmic order - this fact was reflected in the title of his first major work Mysterium Cosmographicum (The Cosmographic Mystery).

Platonic solid model of the Solar System[5]


He also saw in astrology another possible approach to understanding cosmic structures. His astrological activities were motivated neither by financial need nor because he felt obliged to do so. On the contrary, he strongly believed in a connection between the planetary orbits and events on earth, and not only with respect to mundane astrology. He erected and interpreted numerous individual horoscopes, including that of General Albrecht von Wallenstein. He made concrete predictions regarding personal development, although he rejected event prediction. He also made important contributions in the field of astrological aspects. His most important work, the Harmonice Mundi (Harmony of the Worlds) of 1619 contains the philosophical thought behind his astrological understanding.

See also

A stellated dodecahedron



  • Kepler & the Star of Bethlehem (PDF), Chmielewski, 2010
Robert Fludd's Monochord demonstrating ccosmic harmony
Kepler's chart for Wallenstein[6]

Kepler’s own Works

Fundamentis. Astrologiae certioribus nova dissertatiuncula ad cosmotheoriam spectans cum prognosi physica anni ineuntis a natoChristo 1602
It is generally considered the duty of mathematicians to write annual Prognostics...
  • Harmonices Mundi ('Harmonies of the World'), 1618
    • English trans. Duncan, Aiton, Field (1997)

Notes and References

  1. Through several periods of apparent retrograde motion. In Kepler's Astronomia Nova (1609)
  2. The only picture he would accept as looking like himself in reality
  3. Illustration from an article by David Plant. See skyscript
  4. Rodden Rating B. There are different charts existent, see Astro-Databank.
  5. From Mysterium Cosmographicum, Tabula III: Orbium planetarum dimensiones, et distantias per quinque regularia corpora geometrica exhibens, Tübingen 1596.Illustration colored by Adam McLean
  6. Actually his first one, from 1608. He did several more for Wallenstein later on