What's in a Prague street name

Originally published on X on 13 September 2023.

Johannes Kepler was born Weil der Stadt, the “Gateway to the Black Forest”, in 1571, and was the son of a mercenary and a herbalist.

Observing the Great Comet of 1577, and a lunar eclipse in 1580, he soon became fascinated by astronomy.

The picture below is Jiří Jakubův Dačický’s engraving of the comet, as seen over Prague.

While at university in Tübingen, he became a committed Copernican (i.e. he agreed that the planets don’t revolve around the Earth), and also became extremely adept at astrology and horoscopes.

Before his studies were complete, he moved to Graz in 1594 to become a teacher of mathematics. It was here that he met his wife, Barbara Müller, whom he married in 1597.

In 1600, Danish astronomer Tycho Brahe (street in Prague 6, BTW) persuaded Kepler to visit him in Prague and become his assistant. Brahe (great astronomer, not great at maths) was complemented by Kepler (amazing at maths, too short-sighted to observe the stars well).

However, the collaboration would be short-lived, as Brahe died a few days after attending a banquet in Prague in 1601 (either of a urinary problem or mercury poisoning). Rudolph II appointed Kepler to replace Brahe as the imperial mathematician.

Kepler would give Rudolph both astrological and political advice. In return, he was promised what was meant to be a good income, but the imperial treasury was such a mess that what he really got was long periods without being paid and an angry wife.

In 1604, Kepler saw a previously undiscovered supernova, which put paid to the ancient theory that the heavens were unchangeable. Only visible for three weeks, no supernova in the Milky Way has been observable to the naked eye since. It’s known as Kepler’s Supernova.

During the first decade of the 1600s, Kepler also determined the true orbit of the planets for the first time.

In 1611, Rudolph was forced to abdicate by his brother Matthias. Things got pretty grim for Kepler – Matthias was less supportive than Rudolph, Kepler’s research was compromised by religious tensions (he was a Lutheran), and then his son and wife died in quick succession.

He left Prague in 1612 and settled in Linz, working as a teacher and as an expert in astrology and astronomy. In 1613, he remarried, to Susanna Reuttinger.

In 1630, Kepler travelled to Regensburg for work purposes. He became ill, though, and died there a month later. His grave, and the churchyard it belonged to, were destroyed during the Thirty Years’ War. This is a sketch of his tombstone.

A secondary school named after Kepler exists in Prague 6; there’s also a statue of him and Brahe in Keplerova itself.

There are also craters bearing his name on the Moon and Mars, an asteroid, the main university in Linz, and… Kep1er, a K-pop girl group formed through a reality TV show called Girls Planet 999 in 2021.

Hopefully a rival band called Br3he or similar will appear in the next season. (I’m kidding. I think.)