Earth crosses the tail of Halley's Comet on May 18 and 19, 1910. Spectra show poison gas in the tail, newspapers stoke fear, and comet pills sell, but nothing happens.
The story
Halley's Comet returned in 1910, and astronomers calculated that on May 18 and 19 Earth would pass through its tail. Spectroscopy had shown that comet tails contain cyanogen, a poisonous gas, and in early 1910 observers confirmed it in the comet's spectrum. Newspapers ran frightening headlines, and some people sealed their windows, bought gas masks, or took so-called comet pills. Others held comet parties. Astronomers stressed that the tail is so thin that its gas would have no effect.
They were right: nothing happened. The comet was also the first to be photographed on a large scale, giving scientists lasting records of its tail. The episode is a classic example of how modern mass media can spread alarm about a sky event faster than experts can calm it. Many newspapers also printed calm explanations from astronomers, but alarming stories sold better than reassurance.
Why it mattered
Became a standard story of how mass media spread science-based panic in the early 20th century.
Produced the first large set of photographs of Halley's Comet, used to study its tail.
Led astronomers to explain comet science to the public through newspapers, an early case of science communication in a scare.