Johannes Kepler 1571 - 1630, Germany
Astronomer, Mathematician

Johannes did not have an auspicious start in life. He was born in Wurttemberg and was not physically strong, and at the beginning of his education, he was bullied. As well, his parents were poor.

Nevertheless, it soon became evident that Johannes was a bright and intelligent boy, and in due course was offered a scholarship to the University of Tubingen, to study for the Lutheran Church. But besides theology, he also studied mathematics, astronomy, and especially Copernicus' heliocentric theory with considerable satisfaction. As a consequence, he gained a reputation as a strong advocate of Copernicus.

Young Kepler

He relinquished his intention to join the Theology Department at the university when he was offered a position as a mathematics and astronomy professor in Austria. However, his faith in the Church remained firm, as it would throughout his life.

The position in Austria was not highly paid, so Kepler needed to find an alternative source of income. He turned to astrology, at the time a very closely related area of activity. When he was asked to provide an astrological calendar with predictions, they turned out to be extraordinarily accurate. Not only was it good for his financial welfare, but also for his reputation.

In 1597 he was married to a daughter of a wealthy millowner and had two children, but unfortunately, both died, and finally, his wife died as well. Adding to his troubles, in 1598 he was ordered to leave the town because he was a Lutheran. At the time, Europe was in constant religious upheaval, and only Catholics were permitted in Graz, a small town south of Vienna.
But Kepler was a man of deep and enduring faith.

The lord of the area around Graz, Lord Johann Hoffman, had a keen and lively interest in astronomy. He knew of Kepler's abilities and was no doubt well aware of his difficulties in the town. He invited Kepler to accompany him to Prague, all expenses paid. At the time, this was a 10-day trip, not a trip that Kepler could have afforded. The really extraordinary aspect was how a nobleman was associating with an ordinary person, a person from a lower social class. Johann Hoffman also recommended him to Tycho Brahe, the most esteemed astronomer in Europe.

By prior arrangement, he got an invitation from the great man to come as a "participant and companion".

Kepler would have known that Tycho Brahe, had the most extensive astronomical data set in Europe, if not the world. He would also probably know that he was a difficult man to get along with. Tycho was very intelligent and wanted everyone to acknowledge and respect that. Kepler was also very intelligent, but perhaps a touch more humble, as was to be expected.

Tycho Brahe

Tycho Brahe and Kepler had different levels of expertise. And they complemented each other; Tycho with his incomparable data set, accumulated over several decades, and Kepler with his mathematical brilliance and dedication.

Initially, Tycho was very cautious, and kept a close eye on Kepler, allowing him only a selected parcel of data, to see what Kepler could come up with. Tycho did not support Copernicus and wanted Kepler to use the data to offer a different system, a system that Kepler did not agree with.
That all changed in 1601 when Tycho died of a fever, and Kepler gained total access to all the data. He was also appointed to the position of Imperial Mathematician.

By 1609 he was able to verify the orbit of Mars as an ellipse, with the sun at one focus. Later he was able to complete the orbits of all the planets to the extent of predicting the transit of the sun by Mercury and Venus.

Kepler's Solar System

Kepler also made significant contributions to Optics, and in 1611 he published his book "Dioptrice" on his ideas about light and lenses.
Being an astronomer, he had a particular interest in telescopes and presented a design for a telescope, subsequently referred to as Kepler's Telescope.

But life was not easy or peaceful for Kepler. In 1612 Lutherans were told to leave Prague, and Kepler moved South to Linz. He remarried, apparently happily, and they had 7 children.
Adding to his problems was the need to go to Wurttemberg to defend, successfully, his mother against a charge of witchcraft.

Nevertheless, he found time to publish, in 1612, his "Epitome Astronomiae" which presented the results of his dedicated work on Tycho Brahe's data.

His 3 laws of planetary motion, as he set them out, are still taught today.
These laws were also used by Newton when developing the law of Universal Gravitation.

Johannes Kepler later in Life

Kepler died 1630, while on an excursion to collect a debt.

Kepler's three laws of planetary motion are: -

1. The planets move in elliptical orbits, with the sun at one focus.

2. The radius, sun-to-planet, sweeps out equal areas in equal times.

3. Square of the period of the motion is proportional to the cube of the mean distance.

 Click here for Kepler's mathematical skills. 

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