Theory question 203
Latitude, Longitude and Time(a) If the time in London is 08.00 hours GMT and the local time in Addis Ababa is 12.00 noon on what longitude is Addis Ababa? (b) Write explanatory notes on the following: (i) Time zones; (ii) Standard Times; (iii) International Dateline
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(a) Time difference = 12.00 − 08.00 = 4 hours; 4 × 15° = 60°; Addis Ababa is ahead of GMT so it is east: 60°E (in this question's figures).
(b)(i) Time zones: the world is divided into 24 zones each about 15° of longitude wide; places in one zone keep the same time; neighbouring zones differ by one hour; large countries (USA, Russia) have several zones.
(ii) Standard time: the time adopted for a whole country or zone, usually the local time of a central meridian, to avoid confusion of each town keeping its own local time; e.g. West Africa Time (GMT+1) based on 15°E.
(iii) International Date Line: roughly follows the 180° meridian, bent to avoid land; crossing it eastwards one repeats a day (subtract a day), crossing westwards one gains a day (add a day).
Remember 15° = 1 hour and east is ahead of Greenwich.