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How a stick's shadow measured the whole Earth: Eratosthenes, a well and 5,000 stadia Two sticks, one shadow and one distance were enough for Eratosthenes to size the whole planet around 240 BC. On the summer solstice the noon Sun shone straight… History4 min read24 Oct Why random dice rolls draw a perfect fractal: the chaos game and the Sierpiński triangle Pick three dots, then keep jumping halfway towards a randomly chosen one. It sounds like it should leave a grey smudge, but after a few thousand jumps a… Maths3 min read24 Oct Why a dropped stick can find π: Buffon's needle Drop a stick on a floor of planks and count how often it lands across a seam. The count secretly contains π: for a needle as long as the plank width, the… Maths4 min read21 Oct Why cells stay tiny: skin grows with the square, the cell with the cube Double a cell's width and its skin grows 4 times, but the cytoplasm it must feed grows 8 times. Add diffusion, where time grows with the square of the… Biology5 min read17 Oct How a stick and a well measured the whole Earth: Eratosthenes Around 240 BC, the librarian Eratosthenes measured the size of the Earth using a well, a stick and a shadow. At noon on the summer solstice the sun shone… History4 min read11 Oct How dropping needles on a floor reveals the number π: Buffon's needle Toss a match onto a plank floor and ask: does it touch a crack? Do it thousands of times and the fraction that do will quietly spell out π, though no circle is… Maths3 min read4 Oct Why turning a wobbly table can stop it rocking: the quarter-turn proof Your café table rocks. Before you wedge a folded napkin under a leg, try turning the whole table on the spot. On most floors, somewhere within a quarter-turn… Maths5 min read28 Sep How Eratosthenes measured the whole Earth with a stick and a shadow Around 240 BC, Eratosthenes, head of the Library of Alexandria, measured the size of the whole Earth with a stick and a shadow. At noon on midsummer, sticks in… History4 min read27 Sep