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Earth passed through the tail of Halley's Comet on May 19, 1910, as the comet passed near Earth. Halley's Comet is a famous periodic comet, known for its regular appearances in Earth's night sky, making it a celestial event of great historical and scientific interest.
One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen, leading to press speculation that life on Earth could be endangered. Despite reassurances from scientists that the gas would not present any danger, public panic buying of gas masks was recorded, and quack "anti-comet pills" were sold. No harm was done by the comet.
Halley makes a close approach to Earth every 75-76 years. The first certain appearance of Halley's Comet in the historical record is a description from 240 BC, in the Chinese chronicle Records of the Grand Historian or Shiji, which describes a comet that appeared in the east and moved north. It was last seen in 1986, and is expected to return in 2061. More
