Halley’s Comet, 1910: The Night Earth Flew Through a Comet’s Tail

In May 1910, Earth passed directly through the tail of Halley’s Comet — and parts of the public were convinced it was the end of the world.

Astronomers had detected a toxic gas in the tail, newspapers ran scare stories, and swindlers sold “comet pills” and gas masks. The truth: a comet’s tail is so thin it is closer to a vacuum than to air.

Play video: POV: Earth flies through a comet’s tail · Halley 1910Ep. 10 · 1910 — Earth flies through a comet's tail · Halley 1910Time & Space

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Ep. 10 · 1910

POV: Earth flies through a comet’s tail · Halley 1910

Earth flies through a comet's tail · Halley 1910

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What happened

Halley’s Comet returns to the inner Solar System roughly every 76 years, and its 1910 appearance was spectacular. On 18–19 May, Earth was calculated to pass through the comet’s immense tail. Shortly before, spectroscopes had revealed the gas cyanogen in the tail — a compound related to cyanide. That detail, amplified by the press, sparked genuine fear.

The science: a tail of almost nothing

A comet’s tail can stretch tens of millions of kilometres, but it is astonishingly tenuous — the gas and dust are spread so thin that the tail is a better vacuum than anything we can easily make on Earth. The tiny amount of cyanogen that Earth’s atmosphere might encounter was utterly harmless. Astronomers said so clearly at the time; the panic was driven by sensational reporting, not by science.

Fear, profit and a famous coincidence

Opportunists sold anti-comet pills, “comet insurance” and masks to the frightened. The 1910 apparition also carries a literary footnote: the writer Mark Twain was born in 1835, the year of a Halley apparition, and had predicted he would “go out with it” — he died in April 1910, as the comet returned.