(a) Meaning of Great circle: A Great Circle is an imaginary line that divides the earth into two equal halves.
(b) Cha characteristics of a Great Circle:
- Numerous on the globe.
- Runs either vertically or horizontally.
- Could run in any direction.
- They are the shortest distance between any two points on the earth's surface.
- The center of a Great Circle is also the center of the earth.
- Most Great Cires are equal in length.
- The equator is the only latitude that is a Great Circle
- Not always seen as a straight line on a map due to the earth's spherical shape.

(c) Calculation of time, day, and date:
(i) Difference in longitude = 100°+ 10° = 110°. If 1 hour = 15º
\(\therefore\) 110º = \(\frac{110}{15}\) x hr = 7\(\frac{1}{3}\) hours = 7 hours 20 minutes
Time at longitude 10°W is 7 hours 20 minutes behind 5 a.m. = 9:40 p.m.
(ii) Day at longitude 10ºW = Sunday.
(iii) Date at longitude 10°W = 10th April 201l.