Today marks the 534th birthday of Nicholas Copernicus, the Polish astronomer who published the first modern heliocentric theory, in the 16th century.
Although this should be Copernicus' special day - after all, it's not every day a guy has enough candles on a birthday cake to do more damage than Mrs. O'Leary's cow - let's recognize the person who convinced Copernicus to publish his theory, De revolutionibus.
Having heard rumors of Copernicus' theory, the young mathematician Georg Rheticus traveled from Wittenberg to Frombork to meet the secluded amateur astronomer. To make a long story short, Rheticus decided to stay years instead of weeks, became Copernicus' pupil, and, as the cliché goes, the rest is history.
If you are interested in the history of astronomy, do yourself a favor and pick up Dennis Danielson's book The First Copernican (Georg Joachim Rheticus and the Rise of the Copernican Revolution). He gives a thorough account of Rheticus' life and illustrates that "without Rheticus, there would be no Copernicus." There is much more to Rheticus' work after Copernicus, and Danielson covers that career, too.
Before you read the book, be sure to listen to my podcast interview with Danielson. It provides a quick glimpse of one of astronomy's overlooked heroes.