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HEROES OF… SPACE HISTORY’S MOST INFLUENTIAL SCIENTISTS
Johannes Kepler
Kepler’s cosmological model which shows the relative distances of the planets from the Sun
Often overshadowed by Galileo, Kepler was one of the most important figures in the fields of astronomy and physics ever Johannes Kepler was a German mathematician and astronomer who, despite being less well known than scientists like Galileo, played a pivotal role in the founding of modern astronomy. Today, Kepler is best remembered for his three laws of planetary motion (see ‘The big idea’ boxout), as well as his seminal texts on the orbit of Mars, the shape and formation of planets and the ratification of a Sun-centred model of the Solar System – first posited by Renaissance astronomer Nicolaus Copernicus. Kepler was born on 27 December 1571 in the free imperial city of Weil der Stadt, near to modern-day Stuttgart. One of his first
The big idea Despite the underlying reasons being discredited by modern-day astronomers, Kepler’s three laws of planetary motion are still considered an accurate description of the movement of any planet or satellite in space. The three laws are as follows: first, the orbit of every planet is an ellipse with the Sun at one of the two foci. Second, a line joining a planet and the Sun sweeps out equal areas during equal intervals of time. And third, the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. These three laws were revolutionary in the early-17th century as they demonstrated that the Sun was at the centre of the Solar System (which was considered the universe in Kepler’s day) rather than Earth. This laid down the foundation for the important works of Isaac Newton a century later, such as his universal law of gravitation.
A life’s work A journey through the big moments in Kepler’s life
1571
Johannes Kepler is born on 27 December in Weil der Stadt, Württemberg, southwest Germany.
1577
1589
Although a sickly child, viewing the Great Comet of 1577 is a turning point that will inspire his career.
At 18 he enrols at the University of Tübingen’s stift (the theological seminary).
1594
encounters with astronomy came when he was six, observing the Great Comet of 1577. This was followed three years on with a lunar eclipse, which he later recalled greatly inspired him. Kepler stayed in touch with astronomy throughout his schooling, retaining his interest during his time at the University of Tübingen. It was at Tübingen where his superb mathematical abilities became evident and he soon gained a reputation as a skilful astronomer and astrologer (in this era, these disciplines were considered the same thing). Around this time he gained a mentor – Michael Maestlin – and began learning both the Ptolemaic system of planetary motion (which was Earth centred) and also the Copernican system, which was new and revolutionary and controversially placed the Sun at the heart of our Solar System. At the age of 23 Kepler started teaching mathematics and astronomy at the University of Graz. It was during his time here that he published the first defence of the Copernican system, his Mysterium Cosmographicum. The text was not widely read, but it firmly established Kepler as one of the foremost astronomers of the age, as it largely modernised and honed Copernicus’s theories. In 1600 Kepler met someone who would become a key colleague in the formulation of his three laws: Danish nobleman Tycho Brahe, who was building a new observatory. Here he
He starts teaching mathematics at the University of Graz but is dismissed in 1600.
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1596
Publishes Mysterium Cosmographicum, developing the Copernican theory of heliocentrism.
1600
Moves to Prague to work with Danish astronomer Tycho Brahe, who dies the following year.
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