The longitude problem

Timeline

1. 1675Greenwich, Britain · BritainKing Charles II issued a decree establishing the Royal Observatory at Greenwich, appointing John Flamsteed as the first Astronomer Royal; its core mission was to determine the position of the Moon through precise star catalogues, providing data support for solving longitude by the lunar distance method.
2. 1676–1680Royal Observatory Greenwich, Britain · BritainFlamsteed systematically accumulated high-precision star and lunar observation data at Greenwich Observatory, providing the necessary ephemeris tables for the lunar distance method. Meanwhile, Cassini at the Paris Observatory continued to improve the accuracy of the Jupiter satellite occultation method, and the two technical routes formed a competitive dynamic.
3. 1674–1676Atlantic Ocean · European coastsChristiaan Huygens designed a dedicated marine pendulum clock for the Dutch East India Company, which Robert Hooke and others tested for longitude accuracy on real voyages. Experiments showed the clock was severely disturbed by the ship's motion, highlighting the technical bottleneck of the precision clock method in a marine environment and spurring subsequent research on improving balance-spring watches.