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Lost at Sea—The Search for Longitude
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Viewing Ideas
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Before Watching
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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
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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.
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