Theory question 305
Latitude, Longitude and Time(a) What is a Great Circle? (b) Outline three characteristics of a Great Circle. (c) If the time at longitude 100°E was 5 a.m. on Monday, 11th April 2011, what was the: (i) time at longitude 10°W (ii) day at longitude 10°W (iii) date at longitude 10°W?
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(a) A great circle is a circle on the earth's surface whose plane passes through the centre of the earth, dividing it into two equal halves.
(b) It divides the earth into two hemispheres; its centre is the centre of the earth; it is the largest circle that can be drawn on the globe; the shortest distance between two points lies along a great circle (used by ships and aircraft); all meridians and the equator are great circles; infinitely many can be drawn.
(c) Difference = 100 + 10 = 110°; 110 × 4 = 440 minutes = 7 h 20 min; 10°W is west, so time is behind: 5.00 a.m. − 7 h 20 min = 9.40 p.m. (i) 9.40 p.m.; (ii) Sunday; (iii) 10th April 2011.
Subtract time when going west.