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Lost at Sea—The Search for Longitude

Viewing Ideas

Before Watching

1. Review latitude and longitude with students. Have students select a few locations on a map or globe and identify them by latitude and longitude. Give groups of students a marker and an orange or grapefruit, representing the Earth. Ask them to draw and label lines of latitude and longitude on the fruit and locate where East meets West (at 180° longitude—site of the international date line). Have students find a way to make the lines equiangular (for example, they might cut the orange in half and use a protractor to mark equiangular segments). Have students approximate where their city is on the fruit model of the Earth and then confirm latitude and longitude using a map.

After Watching

1. It was commonly believed in the 1700s that the secret to finding your longitude at sea was knowing the time in two places: Your ship's port of origin and its current location. Ask students to explain how knowing the time in two places can help determine longitude.