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TIL Left handed soldiers prepare and throw grenades upside down because of safety pin removal

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neO1d TIL that free nitrogen and oxygen atoms, generated by solar energy in the upper atmosphere, recombine at night to form nitric oxide (NO) in a process that releases a photon, thereby contributing to "Nightglow".
4XEmo TIL that sustaining a second concussion before fully recovering from an initial one (even an extremely minor one) can cause a condition called Second Impact Syndrome, which causes severe brain damage 100% of the time and frequently results in death.
kJpog TIL that in 1977 NASA launched Voyager 1/2 into space with the Golden Record onboard. It contains music, greetings, and images which NASA cannot display online due to copyright law. NASA sent these images to space to represent humanity but cannot show these images to most humans.
Olda TIL Central Park’s rivers and streams are entirely artificial and can be turned on and off.
KOA7R TIL that Arizona started issuing licenses that were good until age 60. Starting at 65, drivers must renew every five years, with a vision test each time.