By Patricia Daukantas

A recent article in the Washington Post pointed out something that OPN readers already know: A 17th-century Danish scientist was the first person to come up with a realistic estimate of the speed of light.

I wrote about this guy, Ole Rømer, in the July/August 2009 issue of OPN. Things get busy in the magazine business, though, so it took a contributing writer in the Post to point out that Rømer died 300 years ago this week – September 19, 1710.

As the Post writer and I both noted, Rømer deduced that light had a very large, but still finite, velocity by studying the motion of the moon Io around the planet Jupiter. After he published his findings in 1676, he turned his attention to other matters, and later scientists continued to refine their measurements of light’s speed until we got the standard that we have today.

One of the challenges that I – or anyone else – have faced when writing about Rømer is that many of his letters and other papers were burned in a building fire after his death. Thus, science historians have lost some valuable primary source material that would have given us additional insight into Rømer’s reasoning and his struggles to gain acceptance of his hypothesis. Still, we know enough about this Danish astronomer to commemorate his place on the timeline of scientific understanding.

2010-09 September, Optics history optics history, light