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TIL the phrase "in the limelight" which refers to being the focus of attention comes from a 19th century device. Calcium oxide known as quicklime is heated in an intensely hot flame until it glows brightly. First as a surveying tool, it allowed for more accurate measurements.

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p8VyG TIL that small bluish-gray band on the horizon during sunset is actually the Earth's shadow being cast on the atmosphere.
n6vb TIL sand sharks get pregnant with up to 50 embryos where one eats all of the others, grows and is born.
R5wg9 TIL I learned about the precursor to the BASIC programming language: the Dartmouth Oversimplified Programming Experiment ... it's DOPE
Mmk0 TIL Horror movie soundtracks sometimes include infrasound, which is sound below the range of human hearing. Even though we can’t hear it we can still feel it and it has been shown to induce anxiety, heart palpitations, and shivering.
4n4R TIL the circular huddle used in todays American Football was created by Paul D. Hubbard, a deaf quarterback, so the other team could not read his hand signals.