Tycho Brahe · 1596
Read the translation (PDF) · Editorial footnotes (PDF)
Before scientific journals existed, astronomers argued, boasted, and traded discoveries by letter. This volume collects the correspondence with Landgrave Wilhelm IV of Hesse-Kassel and his gifted observer Christoph Rothmann — a rare window into science as it actually happened.
The exchanges defend the Tychonic model of the cosmos against both Ptolemy and Copernicus, debate the design of instruments, and compare observations between two rival observatories — Hven and Kassel — as each measured the same sky and compared results.
Running through them is the argument Brahe pressed hardest against Copernicanism: that a moving Earth would require the fixed stars to lie at such distances that, given their apparent sizes, they would have to be impossibly vast. The same reasoning appears in Riccioli’s Astronomia Reformata two generations later, and it was a serious objection — it dissolved only when telescopic optics were understood well enough to show that the measured stellar discs were artifacts of the instrument.
What makes the letters valuable is that they are unpolished. Positions are staked out, conceded, and revised; instruments are praised and criticized; the tone runs from collegial to combative and back. This is the argument before it hardened into published doctrine.
Kassel under Wilhelm IV was the one observatory in Europe that could challenge Hven on its own terms, and Rothmann was a Copernican. The correspondence is therefore not a great man explaining himself to admirers but two well-equipped programs testing each other — the closest thing the sixteenth century had to peer review.
The translated source is the 1596 printing. Many letters — chiefly the Kassel correspondence — were printed twice in the original edition: first in their original German, then in a Latin translation Brahe supplied propter exteros, for the benefit of foreign readers. Each such letter appears here once, translated from the language in which it was composed, with a bracketed editorial note marking where a twin has been passed over.