(a) Highlight any three effects of either rotation or revolution of the earth (b) Give reasons why: (i) all areas north of the Arctic Circle have twenty fou...

(a) Three effects of the revolution of the earth

1. The four seasons: as the earth revolves round the sun with its axis tilted at \(66\tfrac{1}{2}^{\circ}\), the hemispheres are alternately tilted towards and away from the sun, giving spring, summer, autumn and winter.
2. Varying length of day and night: the length of daylight and darkness changes with the seasons at any place away from the equator.
3. Changing altitude of the midday sun and the apparent migration of the overhead sun between the Tropics of Cancer and Capricorn, producing the equinoxes and solstices.

(For rotation, acceptable effects are day and night, deflection of winds/currents by the Coriolis force, differences in time/longitude, and the rise and fall of tides.)

(b) Reasons

(i) Why all areas north of the Arctic Circle have twenty-four hours of daylight on 21 June: On 21 June (the June solstice) the earth is tilted so that the North Pole leans towards the sun and the overhead sun is at the Tropic of Cancer. Because of the \(23\tfrac{1}{2}^{\circ}\) tilt of the axis, the circle of illumination passes beyond the North Pole, so the whole region north of the Arctic Circle remains within the sunlit half of the earth as it rotates. The sun never sets there on that day, giving continuous (24-hour) daylight, the "midnight sun".

(ii) Why areas within the tropics have more sunshine than areas outside the tropics: Within the tropics the sun's rays strike the earth vertically or almost vertically throughout the year, so the sun is high in the sky, its heat is concentrated on a small area, and skies are often clearer for much of the year. Towards higher latitudes the rays strike at an increasingly oblique (slanting) angle, spreading the same energy over a larger area and passing through more atmosphere, so those areas receive less intense and less prolonged sunshine.