Dutch physician, mathematician, cartographer Gemma Frisius was born #OTD in 1555.
He created important globes, improved the mathematical instruments of his day and applied mathematics in new ways to surveying and navigation. Gemma's rings, an astronomical instrument, are named after him. He observed the total lunar eclipse of 3 Mar 1569 and he also discovered the 1572 supernova in Cassiopeia on 9 Nov, which he observed two days before Tycho Brahe.