MacTutor
20th April
On this day in 1543, Copernicus's work De revolutionibus orbium coelestium was published when Rheticus autographed a presentation copy of the completed work. Copernicus died a month later.
On this day in 2009 Google released a Zu Chongzhi doodle.
On this day in 2009 Google released a Zu Chongzhi doodle.