ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Paris Observatory. The observatory, completed in 1672, was funded by King Louis XIV to extend France's maritime power and international trade. In 1672, its director Giovanni Cassini discovered four satellites of Saturn and a division in the planet's rings. He also measured the distance to Mars. In 1863, the observatory published the first modern weather maps and in 1887 began the Carte du Ciel (Map of the Sky) project, an international effort to map the positions of millions of stars, which was superseded by modern astronomical techniques before it could be finished. In 1913, the Paris Observatory used the Eiffel Tower as an antenna and exchanged radio signals with the US Naval Observatory to determine the exact distance of longitude between the two institutions.
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