Eliazar Parra Cardenas Posted almost 2 years ago Adam Savage: How simple ideas lead to scientific discoveries This was truly lovely. Thanks for this new effort of TED-Ed Chris. I do have one technical quibble on the retelling of Eratosthenes' calculation of the Earth's circumference, and I'll mention it here because animation was the ideal medium to fix it and the opportunity was sadly not taken. Around time 2m44s, after stating that one of the 2 sticks made a 7.2deg angle shadow, Adam Savage just jumps to stating that now all you need is to find the distance between the sticks, multiply by 360/7.2=50, and you'll get the circumference. This is NOT straightforward. What happens is simple but not trivial geometry. In a geometric feat of comparable imagination to the physical feat of all the measuring and observation, Erathostenes assumed the sun ray's to be parallel to each other, realized the sun ray on top of the no-shadow stick goes straight to the center of the Earth, and then used a basic theorem of Euclidean geometry ("When a transversal cuts two parallel lines, the alternate interior angles are equal.") to come to that calculation. Admittedly, this is hard to explain with words alone, which is why verbal retellings of the story usually omit it. But it is the perfect use of a good illustration (like the one here http://www.anselm.edu/homepage/dbanach/erat.htm ) --a good animation should do an even better job. I know I'm nitpicking but I see no reason why the animation couldn't at least hint at the beautiful geometry underneath this feat of scientific thought (it's OK to hand-wave detail but at least wiggle your fingers). Please don't be afraid of including a lot of detail in your animations. As you said in your TED-Ed introduction: hello replay button (and frame-by-frame viewing).