Heroes of space Johannes Kepler

SPACE HISTORY’S MOST INFLUENTIAL SCIENTISTS

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: fi rst, 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.

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 fi gures in the fi elds 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 ratifi cation of a Sun-centred model of the Solar System – fi rst 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 fi rst 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 fi rst defence of the Copernican system, his Mysterium Cosmographicum. The text was not widely read, but it fi rmly 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

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

Although a sickly child, viewing the Great Comet of 1577 is a turning point that will inspire his career.

1589

At 18 he enrols at the University of Tübingen’s stift (the theological seminary).

1594

He starts teaching mathematics at the University of Graz but is dismissed in 1600.

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.

Top 5 facts: Johannes Kepler

1Family Johannes Kepler and his first wife, Barbara Müller, had five children in total. However, the first two – named Heinrich and Susanna – both died in infancy. The following three survived. He married a second time in 1613.

2Banishment Kepler’s belief in a Sun-centred Solar System – along with his deep-rooted Protestantism – saw him banished from the Austrian, heavily Catholic city of Graz in August 1600.

A remnant from a massive supernova observed by Kepler back in 1604

wished to utilise Brahe’s extensive observations of Mars to run a test to back up his evolution of the Sun-centred Copernican system. Following Brahe’s untimely death in 1601, he succeeded him in becoming imperial mathematician to Emperor Rudolf II, a time in which he published works on optics and techniques for observing stars and planets, as well as his landmark 1609 text A New Astronomy, in which he introduced the first two of his three laws of planetary motion.

After the death of the emperor in 1612, Kepler moved to Linz. It was here, seven years later, that he published Harmonices Mundi, a text that while filled with much erroneous material as determined by modern science, did include his third and final law of planetary motion. He later completed a comprehensive star catalogue and planetary table started with Brahe in 1600.

Kepler died on 15 November 1630 in Regensburg, Germany. Despite his impressive work, his three laws were not immediately accepted by the astronomical community, with notable figures such as Galileo and René Descartes ignoring them. It was not until the late-17th century that astronomers like Isaac Newton started to adopt them. 3Supernova Kepler was the first A 31km (19mi)-diameter astronomer to observe the crater on the Moon that is named after Kepler SN 1604 star go supernova in October 1604. Two years later he described it in detail in his text De Stella Nova.

4Rejection When Kepler published two of his three laws in his groundbreaking work Astronomia Nova at first he was ridiculed and ignored by the majority of the scientific establishment, including Galileo Galilei.

5Mountains In New Zealand’s Fiordland National Park there’s a mountain range named after Kepler in tribute to his extensive contributions to the field of astronomy. “ kepler is best remembered for his three laws of planetary motion and seminal texts on the ratification of a sun-centred solar system”

1601

Kepler is appointed Emperor Rudolf II’s imperial mathematician in Brahe’s stead.

1609

Two of Kepler’s three laws of planetary motion are published in Astronomia Nova, based largely on the movements of Mars.

1611

In the wake of Galileo’s success, Kepler puts forward a new design for a telescope with two convex lenses.

1612

Kepler returns to his hometown to defend his mother, a healer, against charges of witchcraft.

1621

Publishes Epitome Astronomiae, which is a compilation of all his other work on heliocentrism.

1624

As per Brahe’s dying wish, Kepler completes an astronomical table that is far more accurate than previous models.

1630

Johannes Kepler dies in Regensburg on the way to collect a debt, aged 58.