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The Challenge: Measure Latitude and Longitude

Measuring Longitude

It's easy to work out your longitude using a radio, watch and sundial, but as castaways on Capraia we had none of these. Even though we built a radio, we still needed some sort of timepiece, so we made a pendulum of a certain, known length which we knew would swing with a fixed frequency (determined by this length).

The Earth rotates one full turn (360° of longitude) in one day. It therefore turns one degree of longitude in 1/360th of a day, or every four minutes. To calculate your longitude, you therefore simply need to work out the time difference between noon at your location and noon at the Prime Meridian.