Theory question 203
Latitude, Longitude and Time(a) Distinguish between local time and standard time. (b) The local time of Town A, located on longitude 70°E and latitude 45°N, is 7.46 p.m., calculate the longitude of Town B on the same latitude when its local time is 5.30 a.m.
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(a) Local time is the time of a place by the sun on its own meridian (noon when the sun is overhead), so it changes by 4 minutes for every degree of longitude; standard time is the time adopted for a whole time zone or country, usually the local time of a central meridian, so it changes by whole hours between zones; places in one zone share one standard time but have different local times.
(b) Time difference = 7.46 p.m. − 5.30 a.m. = 14 h 16 min = 856 minutes; 856 ÷ 4 = 214° of longitude; B is behind A so it lies 214° west of 70°E: 214 − 70 = 144°W.
Find the time difference in minutes, divide by 4, then move west because B's time is earlier.