From 2009 to 2017 there was a small museum in a little passage near the east end of Charles Bridge, at Karlova 4, in a house where the German astronomer Johannes Kepler (1571-1630) used to live.

This was no doubt one of the world’s smallest museums, consisting of one room with a few text panels in Czech and English.

But these text panels were very well done, giving a good introduction to Kepler’s life and work, with emphasis on the highly productive time he spent in Prague from 1600 to 1612.

Plaque on the house at Karlova 4 in Prague

While reading through the text panels and looking at the diagrams and pictures I was reminded of how I felt in school when I first learned about Kepler’s three laws of planetary motion: I was astounded by the first two laws and baffled by the third, much like the reactions of Kepler’s contemporaries when he first proposed the laws in the early seventeenth century.

Kepler’s first law is that the orbit of every planet is an ellipse with the sun at one of the two foci. I remember finding this counter-intuitive at first (why should the sun be at one focus and why isn’t there anything at the other focus?), though by now it seems rather obvious.

The same with the second law: why should a line joining a planet and the sun sweep out equal areas during equal intervals of time? Actually, this is just another way of saying that a planet moves faster when it is closer to the sun, but it took a while for this to sink in. I’m not an astronomer, obviously.

I’m also not a mathematician, otherwise I wouldn’t have been so baffled by Kepler’s third law, which simply (simply?) explains why Mercury zips around the sun at nearly 48 km per second, while the Earth goes less than 30 and Neptune goes less than 6 km per second. I naively thought that planets having greater distances to travel should try to go faster, not slower, and I suppose that as a poor innocent humanities major I was intimidated by the square of one thing being directly proportional to the cube of something else, though it isn’t really all that mysterious and was explained very well in the museum.

(Of course planets can’t “try” to do anything; they just do what they’re told — by gravity or the curvature of space-time or whatever.)

My ticket to the Kepler Museum

Since this was a small museum the admission price was quite reasonable. As a “senior” I paid all of 20 CKZ, which was less than one Euro. For this I got not only admission to the museum, but also an attractive and informative ticket indicating that I entered the museum at exactly 11:42:04 on April 9, 2011, when the sun was in Beran-Aries and the moon was in Rak-Cancer. The moon phase on that day was a waxing crescent, sunset was at 18:46 and sunrise at 5:20. Old Bohemian Time was 16:56, Sidereal Time was 0:51 and the Babylonian Hour was 6. Any questions?

Although the Kepler Museum no longer exists, its text panels were transferred to the Czech National Technical Museum, where they were installed in 2018.

In a later phase of his life Kepler lived in the German city of Ulm for two years.

Have I mentioned that Kepler successfully defended his mother in court when she was indicted on charges of witchcraft? More on that some other time.

My photos in this post are from 2011. I revised the text in 2019.

See also: The Weikersheim Planetary Trail.
See more posts on Prague, Czech Republic.