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 return, and how a German farmer, John Winthrop at Harvard, and Jamaican polymath Francis Williams confirmed it. It then turns to the 1986 armada of Giotto and Vega probes that revealed a 4 percent albedo crust, a mere 10 percent active surface, and a deuterium ratio that ruled out Halley-type comets as the source of Earth’s oceans. It closes with the retrograde orbit, Bessel’s non-gravitational jet effects, the Eta Aquariids and Orionids, and projections that the comet will evaporate, fracture, or be ejected within tens of thousands of years.

• Why a short-period comet visible to the naked eye is a perfect generational spectacle
• The hidden tribute to the comet in a 1760 portrait uncovered by X-ray imaging
• How sublimation builds a pitch-black insulating crust over ancient ice
• Asymmetric outgassing as unpredictable rocket thrusters that delay perihelion by days
• Aphelion in late 2023 and the next return in July 2061