Finding the Speed of Light: The 1676 Discovery that Dazzled the World is a children's picturebook about a momentous event in the history of science - when Ole Romer
deduced that light traveled at a speed (and wasn't simply instantaneous) using little more than a home-built telescope and an ordinary clock.
The first person to come close to working this out was a Danish fellow by the name of Ole Romer
, who worked in the Royal Observatory in Paris in the 17th century.
Working at the Danish Uraniborg Observatory in 1671, Ole Romer
decided to test Galileo's claim that telescopic observations of Jupiter's moons could be used to precisely keep time.