URANOS: Johannes Kepler

Johannes Kepler (1571-1630)

German-Austrian mathematician, astronomer, and researcher of optics. His principal achievement is the formulation of three laws of planetary motion, called Kepler's Laws. He derived them after lenghty and complex calculations, based on the most accurate, at his time, observations of planet positions (especially of Mars ) performed by Danish astronomer Tycho de Brahe (Kepler was his assistant for some time). These laws, which constituted a basis for numerical tables allowing for a very accurate predictions of planet positions, became decisive arguments in favor of the Copernicus heliocentric theory.

His major works include:

1596:

In "Mysterium Cosmographicum" ("The Cosmographic Mystery") he supported the Copernicus theory on the basis of his first (unfortunately, wrong) mathematical model of planetary orbits, based on a structure of regular polyhedrons (Platonic solids).

1604:

In "Astronomia pars Optica" ("The Optical Part of Astronomy") he described, among others, the phenomenon of atmospheric refraction, the theory of lenses and a modern theory of vision.

1609:

Published "Astronomia Nova" ("New Astronomy"), where he described the first two laws of planetary motion:

Kepler's first law: The planets move in elliptical orbits with the Sun at one focus.
Kepler's second law: The straight line from the Sun to the planet sweeps out equal areas in equal times
(in the derivation of this law Kepler used an original calculation technique anticipating integral calculus, invented much later by Newton and Leibniz).

1611:

In "Dioptrice" ("Dioptrics") he described construction of telescopes, including his new telescope (Kepler's telescope - with two convex lenses).

1619:

In "Harmonice mundi" ("Harmony of the World") he described the third law of planetary motion:

Kepler's third law: The square of a planet's orbital period is proportional to the cube of its mean distance from the Sun
(this law became the basis for the derivation of the law of universal gravitation by Newton).

1617-1621:

Published a widely used textbook on heliocentric theory - "Epitome Astronomiae Copernicanae" ("Epitome of Copernican Astronomy").

1627:

Published "Tabulae Rudolphinae" ("Rudolphine Tables"), predicting with great accuracy future positions of the planets.

Additional information about Kepler can be found in his extensive biographies at The Galileo Project at Rice University, USA, and at MacTutor: Archive of the History of Mathematics site in Scottland.

Named after Kepler were: a small, though easily visible crater (31 km diameter) on the near side of the Moon (in the vicinity of the Copernicus crater), a large crater (219 km diameter) on Mars , a rocky ridge Kepler Dorsum on Phobos (the larger of the Mars moons), a star Kepler's Nova (Sn 1604/V843 Oph) in the constellation Ophiuchus, which he observed from the time of its appearance in 1604, an asteroid 1134 Kepler. [ZK]

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Last update: 06.VI.2001