1644-1710

Danish Astronomer and Physicist

Ole Römer is famous for demonstrating the finite velocity of light. He produced various scientific instruments including an improved micrometer, planetaria, the first transit circle, and an alcohol thermometer.

Römer was born on September 25, 1644, in Aarhus, Denmark. In 1662 he matriculated at the University of Copenhagen, where he studied astronomy and mathematics with Thomas (1616-1680) and Erasmus Bartholin (1625-1698). He lived at the home of Erasmus while a student, eventually becoming his personal assistant and marrying his daughter.

In 1671 Römer met Jean Picard (1620-1682) and accompanied him to the island of Hven to assist in redetermining the position of Tycho Brahe's (1546-1601) observatory Uraniborg. To this end they made measurements, in conjunction with those by Giovanni Domenico Cassini (1625-1725) in Paris, of a series of eclipses of Jupiter's moon Io. Römer returned...