The race to define longitude with time ⚓️ For centuries, mariners had tried to measure their position at sea using the sun and stars. This works for latitude, but longitude isn't so easy as there's no natural equivalent to the equator. Where does longitude begin and end? Where is your zero point? The idea was to use a clock as a reference. The Earth rotates on its axis once every 24 hours, so it's 360 degrees divided by 24 gives us 15 degrees per hour. If you know your local time where you are,