From royalsociety https://twitter.com/royalsociety on Twitter: It was #onthisday 1610, Italian polymath Galileo Galilei observed the 3 largest moons of Jupiter for the first time. He discovered the fourth on 13 January. https://en.wikipedia.org/wiki/Galileo_Galilei?utm_source=social&utm_medium=hootsuite&utm_campaign=standard https://twitter.com/royalsociety/status/949936202798465024/photo/1 https://chirp.cooleysekula.net/attachment/47034