Theory question 305
The Earth and Solar System(a) With the aid of a diagram, explain eclipse of the moon. (b) State three characteristics of Great Circles. (c) Outline three uses of Great Circles.
Show the model answer
(a) An eclipse of the moon (lunar eclipse) happens when the earth comes directly between the sun and the moon, so the earth's shadow falls on the moon and blocks the sunlight it reflects; it occurs at full moon; it may be total (moon in the umbra) or partial (moon partly in the penumbra). Diagram: sun - earth - moon in a straight line with the earth's shadow cone covering the moon.
(b) A great circle divides the earth into two equal halves (hemispheres); its plane passes through the centre of the earth; it is the largest circle that can be drawn on the globe; the Equator is the only latitude that is a great circle; any pair of opposite longitudes forms one; there can be an infinite number of them.
(c) The shortest distance between two places lies along a great circle, so they are used for planning air routes and sea routes; navigation; saving fuel and time; used in calculating distances; telecommunication routes.
Draw the shadow cone clearly.