(a) Explain the following terms; (i)Rotation of the earth (ii)Revolution of the earth (iii)Equinox (b) Outline three effects of the revolution of the earth.

Answer Details

(a) Explanation of terms

(i) Rotation of the earth: This is the spinning or turning of the earth on its own axis from west to east. The earth completes one rotation in approximately 24 hours (one day). It is responsible for day and night and for the apparent rising of the sun in the east and setting in the west.

(ii) Revolution of the earth: This is the movement of the earth in its orbit around the sun from west to east. The earth completes one revolution in about \(365\tfrac{1}{4}\) days (one year). The axis is tilted at \(66\tfrac{1}{2}^\circ\) to the plane of the orbit (or \(23\tfrac{1}{2}^\circ\) from the vertical).

(iii) Equinox: This is the time (about 21 March and 23 September) when the sun is overhead at the equator, so that day and night are of equal length (12 hours each) all over the world. "Equinox" means "equal night".

(b) Three effects of the revolution of the earth

1. It causes the sequence and changing of the four seasons: spring, summer, autumn and winter.
2. It causes variation in the length of day and night at different times of the year (except at the equator).
3. It causes the apparent northward and southward migration of the overhead (vertical) sun between the Tropic of Cancer and the Tropic of Capricorn, and it determines the calendar year, leading to the introduction of the leap year.