John Banville, in his novel Kepler, describes the scene like this: "Tycho, with his silence and his stare, his gleaming dome of skull and metal nose, seemed more than human, seemed a great weighty engine whose imperceptible workings were holding firmly in their courses all the disparate doings of the castle and its myriad lives."
The year was 1600; the castle was Benatek near Prague; and the occasion was the first meeting between a young Kepler and the other great astronomer of that era, Tycho Brahe.
Tycho was born to a noble Swedish family in 1546. An eclipse of the sun when he was still a student at Copenhagen University directed his attention to astronomy, and being unconvinced by current theories on the motions of the planets, he decided the only way to gain an understanding was by constant observation. To this task he devoted the remainder of his life.
In 1576, by which time Tycho had established a considerable reputation in his field, he was given Hven Island, close to Elsinore, by King Frederick II of Denmark, and here he built Uranienborg, the "Castle of the Heavens", a Mecca for astronomers in succeeding decades. Tycho's observations over 20 years at Uranienborg, without the telescope, yet to be invented, were accurate enough for him to determine the length of the year to within one second.
Tycho was not without his eccentricities. Banville's cryptic reference to a "metal nose" recalls the fact that Tycho lost his nose in a duel as a student, and thereafter wore a large artificial replacement made of gold and silver - a device which rivals unkindly suggested he used as an instrument for making observations. He also kept a hunch-backed fool called Jeppe, whom he is said to have rescued from being roasted alive by a band of mercenaries.
After the death of his patron Frederick in 1597, Tycho moved to Prague as court mathematician to the Emperor Rudolph II, where three years later, as we have seen, Kepler joined him as a pupil. But he did not long survive their meeting. Tycho Brahe died on October 24th, 1601, which makes today the quatercentenary of his death at Benatek.
It was left to Johannes Kepler, his successor as mathematician to the Emperor, to put Tycho's carefully-crafted observations to spectacular use. With their help he rendered heliocentric astronomy almost indisputable, deduced the mathematical rules by which the system worked, and in 1609 demonstrated that the orbits of the planets around the sun were not circles, but ellipses.