Rømer, Ole Christensen
The Dane Ole Christensen Rømer (1644 - 1710), son to a merchant and skipper was an astronomer.
To measure the (finite) speed of light, he started a series of observations of eclipses of Jupiter's moon Io, but he never gave a value for the speed. However, using Rømer's data, Christiaan Huygens deduced that light travels approximately 212,000 km·s-1. This is about 30% smaller than the true value.
See also
Last modified:10 January 2026 2.51 p.m.