The Story of Longitude Chaired by Bruce R. Mehlman Picture yourself at high noon at the OK Corral. If you knew what time it was at that moment in London, simple arithmetic would tell you the exact longitude of Tombstone, Arizona. Time is money.
Longitude is money.
Early longitude determination was by dead reckoning. Dead reckoning is based on the fact that if you know where you were, how fast you went, and in which direction, then you know where you are. Galileo proposed that the positions of the satellites of Jupiter could be used to tell the time. This method proved useful only on land, both because of the difficulty of telescopic observation at sea and because to determine the longitude of a fixed location only observation of local times of an eclipse was needed, not prediction of the exact time of eclipses. This was the method used for the first accurate longitude determination, of Tycho Brahe's observatory relative to the Paris meridian.