What made measuring longitude so difficult for early explorers?
You’ve probably heard stories of people navigating by the sun, moon, and stars. The sun and moon can be used to easily find the direction someone was traveling, and the stars could be used to determine latitude (how far north or south of the equator a location is). Longitude is a different story for early explorers, because of one simple thing: time. Longitude is calculated by observing the difference in local time between two points. In order to determine the time difference, navigators first needed an accurate way of keeping time. Every hour, the earth rotates through 15 degrees longitude.Although mechanical clocks have been around since the 9th century, they were either too bulky or delicate for sea travel. It wasn’t until the 18th century that John Harrison invented the first clock suitable for determining longitude at sea. As marine clocks became more common, it became easier and easier for navigators to find their true place in the world.
