Daily History Challenge · No. 119 · Sunday 25 October 2026 · Gauntlet
Puzzle No. 119: Gauntlet
The Sunday Gauntlet: three before or after calls, four events to order and a final When? on Kepler's laws of planetary motion.
Act 1: Chain, against The Austro-Prussian War and the North German Confederation (1866 CE)
Before The Austro-Prussian War and the North German Confederation
Before The Austro-Prussian War and the North German Confederation
Before The Austro-Prussian War and the North German Confederation
Act 2: Order, earliest first
Act 3: When?
Working from the unprecedentedly precise observational data of his late employer Tycho Brahe, the German astronomer Johannes Kepler transformed the heliocentric model into a quantitatively accurate description of the heavens. In Astronomia Nova (1609), his long struggle to reconcile Brahe's observations of Mars with circular orbits led him to abandon the perfect circles assumed since antiquity. He proposed that planets travel in ellipses with the Sun at one focus (his first law) and that a line joining a planet to the Sun sweeps out equal areas in equal times (his second law). A decade later, in Harmonices Mundi (1619), he added the third law: the square of a planet's orbital period is proportional to the cube of its mean distance from the Sun. Together these laws replaced the cumbersome epicycles of both Ptolemy and Copernicus with a simple, predictive mathematical framework, and treated planetary motion as a physical problem driven by forces rather than mere geometry. Kepler's laws became the empirical foundation that Newton would later explain through universal gravitation, and they remain central to celestial mechanics and spaceflight today.