Mark Twain was born in 1835 as Halley's Comet blazed overhead and predicted he would go out with it; he died in 1910 on its return. This deep dive uses that story to frame the comet as an icy metronome for human history, tracing it from Han Dynasty Chinese records in 240 BC through Rome in 12 BC, the Bayeux Tapestry and the Battle of Hastings in 1066, the founding of Debre Berhan in Ethiopia in 1456, and the cyanogen gas panic of 1910 that sold comet pills and rooftop end-of-the-world parties. It also settles the pronunciation debate, noting biographer Colin Ronan's evidence that Halley himself likely rhymed his name with crawly.

The episode explains how Tycho Brahe's 1577 parallax measurement moved comets beyond the Moon, how Edmond Halley applied Newton's gravitation to 24 comet observations to link 1531, 1607, and 1682 and predict a 1758 ...