Oldie, but a goodie. Come spend a couple minutes with Carl Sagan as he explains how Eratosthenes figured out the circumference of the earth and that it truly was a sphere!
The pacing is a little slower than we're used to these days, but it's a relaxing five or so minutes. Rebel against the attention economy for a moment this Friday and indulge yourself.
Eratosthenes is also the person thank for the fundamental properties, to this day, of prime-sieving algorithms. His algorithm generates all the prime numbers, albeit very slowly. Nowadays there are some improvements for finding all primes up to a certain size (algorithms that run more quickly), but they are fundamentally just fancier versions of Eratosthenes’ method, with the same core idea that’s at least 2200 years old.
The original sieving method to generate primes is so straightforward that 7/8 year olds could do it, it’s nice