In 1676, the Danish astronomer Ole Romer did something quite remarkable for his time – he measured the speed of light. Although his value was not very accurate, it was the first demonstration that light does not travel instantaneously, a belief that been held by almost everyone from Aristotle on down. In this post I will describe how Romer did it, and then describe my little experiment to reproduce his measurements and calculations.

The history of mathematics has many instances where someone has posed a problem for the mathematical world at large to solve, and the problem was not resolved for decades, or even centuries. Often, new mathematics has been discovered in the process of working out a solution.
This post is the story of one such case, the so-called Basel Problem, first posed as a challenge to European mathematicians in 1644. It withstood all attempts to solve it until, in 1734, young Leonard Euler found the answer. As the reader will see, Euler’s solution is a work of astonishing ingenuity, even though the level of the mathematics does not go beyond Algebra I.