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TIL many EXIT signs contain a radioactive isotope of hydrogen, tritium gas. This allows for radioluminescence, which makes the sign glow as a result of low-level beta radiation from the tritium decay.

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4kKr6 TIL Ketchup used to be sold as medicine claiming to cure diarrhea
KOJ0a TIL, On April 18, 1962. An unknown object was widely witnessed and tracked on radar as it zoomed across the United States, travelling from east to west and landing in Utah, before it exploding over Nevada. Government claimed it as a meteor while released United States Air Force classed it as unknown
O4Vg TIL that for hundreds of years, “Computer” was a job title for a person who did math problems all day.
jQyE TIL that “buttload” is an actual measurement - 126 gallons
LQd4d TIL a survey found that 56% of commercial pilots admitted to sleeping while flying and 29% had woken up to find the other pilot asleep as well