Johannes Kepler

The Johannes Kepler memorial plaque is mounted on the facade of a house at Karlova 4 in Prague's Old Town, a building once registered under the old land number 188. A bronze plate with a relief portrait of the astronomer marks the years he lived and worked in this building at the height of his career.

Why was Kepler in Prague at all?

Johannes Kepler, a German astronomer, mathematician and astrologer, came to Prague to join the court of Emperor Rudolf II of Habsburg. He first worked as an assistant to the Danish astronomer Tycho Brahe, who had been carrying out celestial observations there on the emperor's behalf. After Brahe's death, Kepler took over his position and became imperial mathematician and astrologer at Rudolf II's court. He lived in the house at Karlova 4 from 1607 to 1612 - the exact period commemorated by the plaque today.

What did Kepler discover while living in this house?

It was in Prague, during the years marked on the plaque, that Kepler formulated the first two of his three laws of planetary motion: the law stating that planets travel in elliptical orbits, and the law describing how a planet's speed changes with its distance from the Sun. He published these findings in Astronomia nova, breaking with centuries of tradition that had described the motion of celestial bodies using perfect circles. Kepler's laws later became one of the foundations on which Isaac Newton built his theory of gravity.

What does the plaque look like and when was it made?

The plaque is a bronze plate bearing a relief portrait of Johannes Kepler. It was created by S. Hajerová and unveiled in 1971 on the initiative of the Prague Institute for the Care of Monuments. The Czech-language inscription states that Johannes Kepler lived in this house from 1607 to 1612, and that during that time he discovered the first two laws of planetary motion around the Sun.

What else was housed in this building?

For many years, the house at Karlova 4 was also home to a small Kepler Museum, dedicated to his Prague period and scientific legacy. The museum closed in 2017, and its exhibits were transferred to the National Technical Museum in Prague. The building itself stands on one of the oldest and busiest streets of Prague's Old Town, linking Old Town Square with Charles Bridge, so the plaque is passed daily by huge numbers of visitors walking between the city's two main landmarks.

Frequently asked questions

Who was Johannes Kepler? A German astronomer, mathematician and astrologer, one of the leading figures of the 17th-century Scientific Revolution, best known for his laws of planetary motion set out in Astronomia nova, Harmonice Mundi and Epitome Astronomiae Copernicanae.

Where exactly is the plaque located? On the facade of the house at Karlova 4 in Prague's Old Town, close to Charles Bridge.

How long did Kepler live in this house? According to the plaque's inscription, from 1607 to 1612, during his time serving at the court of Emperor Rudolf II.

Can the museum once dedicated to Kepler still be visited here? No - the Kepler Museum that operated on this site was closed in 2017, and its exhibits were moved to the National Technical Museum in Prague.