Many solutions were proposed for how to determine longitude at the end of an exploratory sea voyage and hence the longitude of the place that was visited (in case one would want to revisit it, place it on a map, or more urgently, avoid known marine hazards). The practical methods relied on a comparison of local time with the time at a given place (such as Greenwich or Paris). Many of these methods relied on astronomical observations relying on the predictable, "clockwork" nature of motions of heavenly bodies. By measuring locations of the fixed stars, local time could be reckoned. The remaining problem was to accurately estimate the time at the given (now distant) place.
Harrison set out to solve the problem in a direct way: by producing a reliable clock that could keep the time of the given place across a long sea journey.
