When you admire the beautiful gardens of Prague Castle at the Queen Anne’s Summer Palace, know that two of the greatest astronomers of our history, Tycho Brahe and his assistant Johannes Kepler, observed the stars together here. Yes, this is where Kepler discovered the first two laws of planetary motion. In the most beautiful baroque library in the world, the Clementinum, we have a memory of Kepler in the form of several of his writings with a personal dedication to his friends at Charles University. A living legacy of Kepler’s legacy is the Prague headquarters of the European Union Space Programme Agency, which runs the Copernicus Earth observation programme. It sounds like a fairy tale: the poor, short-sighted son of a mercenary and an herbalist accused of witchcraft became one of the greatest astronomers in history thanks to his talent and diligence. His three laws of physics about the movement of the planets around the sun are now known to the entire scientific world. Two of them were formulated by this German mathematician and astronomer in Prague. In 1600 he joined the court of Emperor Rudolf II in Prague as an assistant to the renowned astronomer Tycho Brahe. Both astronomers lived in Prague at Hradčany, where the owner of the house, Jakub Kurz of Senftenava, added an observatory to their house. Not only the observatory, but also the house itself can no longer be found on this site, having been demolished and filled in long ago. However, Kepler and Brahe also used the nearby Queen Anne’s Summer Palace to observe the night sky, where Emperor Rudolf II also had an astronomical observatory built. Today, you will find exhibitions of fine art and craftsmanship in the Summer Palace. Emperor Rudolf II, who was Kepler’s and Brahe’s patron, demanded that scientists constantly produce horoscopes and trusted them implicitly. Kepler was rather sceptical about them, but they represented a welcome source of income for him, so he compiled them with a slight sense of embarrassment not only for the emperor but for many other interested parties. His care for the emperor, however, allowed him the freedom to research. Kepler was also given the horoscope of Duke Albrecht of Wallenstein to compile, but he submitted his birth data anonymously. Kepler was thus able to add to the horoscope without fear that its holder was an intelligent personality with pronounced anti-social tendencies, predatory and morbidly ambitious. In 1625 Kepler corrected the already identified horoscope on the basis of new observations and warned Albrecht that the beginning of 1634 would be critical for him. On Saturday, 25 February 1634, Albrecht von Wallenstein was murdered in one of the town houses in Cheb. This is vividly described by Friedrich Schiller in his Wallenstein trilogy, from which the famous saying I know my Pappenheims comes. The mutually beneficial cooperation between the astronomers (Brahe was the most accurate observer of the starry sky of his time, and the short-sighted Kepler was a brilliant mathematician) did not last long. Tycho Brahe died less than two years after Kepler’s arrival in Prague. He was buried in the Church of Our Lady before Týn in Old Town Square and his tombstone can be found at the first south pillar of the nave. Kepler was then appointed imperial court mathematician. In 1607, he moved with his family to the house U Francouzské koruny in Charles Street, on the facade of which we can now find a massive bronze plaque commemorating the astronomer’s stay. There is also a Kepler Museum in the courtyard of the house, and a small Kepler fountain in the courtyard. It was created by students of the Faculty of Mathematics and Physics of Charles University together with Czech sculptor Zdeněk Kolářský. At the time when Kepler moved into Karlova Street, there was a lot of building activity. The Jesuit Fathers were building their Clementinum complex. The Church of the Most Holy Salvator and the Vlašská Chapel were already standing, while the Baroque Library, where several of Kepler’s writings were eventually housed, was yet to be built and became one of the most beautiful libraries in the world. Among the most precious works housed in the Clementinum today is the Ad Vitellionem Parali-pomena. Omnibus Astronomia Pars optica traditur with Kepler’s handwritten dedication to his friends, the dean and other professors of the University of Prague. After the death of Emperor Rudolf II in 1612, Kepler moved out of the country and visited Prague for the last time in 1627, three years before his death, to present the completed astronomical tables ordered by Rudolf II to Emperor Ferdinand II. He stayed at the Velryby Inn in Mostecká Street, almost in the shadow of the majestic Malostranská Mostecká Tower. It wasn’t like when he and Tycho went to the U Mecenáše pub in Lesser Town, but even so, Prague said goodbye to the man who had looked up to the heavens.