History of longitude instant in time, local solar time at a location varies by one hour for every 15 degrees change of longitude (360 degrees divided by 24 hours), there is a direct relationship between time and longitude. If the navigator knew the time at a fixed reference point when some event occurred at the ship's location, the difference between the reference time and the apparent local time would give the ship's position relative to the fixed location. Finding apparent local time is relatively easy. The problem, ultimately, was how to determine the time at a distant reference point while on a ship.
Longitude rewards Longitude Act only addressed the determination of longitude at sea. Determining longitude reasonably accurately on land was, from the 17th century onwards, possible using the Galilean moons of Jupiter as an astronomical 'clock'. The moons were easily observable on land, but numerous attempts to reliably observe them from the deck of a ship resulted in failure. For details on other efforts towards determining the longitude, see History of longitude. The need for better navigational accuracy for increasingly longer oceanic voyages had been an issue explored by many European nations for centuries before the passing of the Longitude Act in England