
Albert Einstein’s Sci-Fi Stories - coloneltcb
http://www.newyorker.com/tech/elements/albert-einsteins-sci-fi-stories?mbid=social_twitter
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ant6n
"By the time (...) in 1846, it was well known that light had a finite speed.
Ole Rømer, a Danish scientist working in Paris, had proved as much more than a
century and a half earlier."

I found this intriguing, how did he measure it? Well it turns out Romer wanted
to create an absolute clock that could be used in navigation -- the clock
being the orbit of Io around Jupiter, whose orbital period is a bit less than
2 days. They figured that if they had exact tables into the future, you could
get the absolute time anywhere on earth, and thus estimate your longitude.
Romer found that during the seasons, the orbit moved 11 minutes ahead, then 11
minutes behind relative to the mean predicted orbit. He figured that this is
due to the finite speed of light; and if you know the measure of an AU you get
that c = 2*AU/22min.

source:
[http://www.amnh.org/education/resources/rfl/web/essaybooks/c...](http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_roemer.html)

