Theory question 203
Latitude, Longitude and Time(a) With the aid of diagrams, explain the following terms in relation to the shape of the earth. (i) Sunrise and sunset. (ii) Circumnavigation. (b) Calculate the distance between town A (latitude 5°N) and town B (latitude 10°N) if they are both situated on the same meridian.
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(a)(i) Because the earth is a sphere rotating from west to east, the sun rises earlier at places to the east and later at places to the west; sunrise and sunset happen at different times along different longitudes; if the earth were flat the sun would rise at the same time everywhere. Diagram of a globe lit from one side.
(ii) Circumnavigation: travelling continuously in one direction (e.g. eastwards) round the earth brings the traveller back to the starting point, as Magellan's expedition did; this is possible only on a sphere. Diagram of a route round a globe.
(b) Both are north of the Equator: 10° − 5° = 5°; 5 × 111 km = 555 km (5 × 69 miles = 345 miles).
Subtract latitudes when both places are in the same hemisphere.