(a) Explain the following terms: 1.rotation of the earth; 2.revolution of the earth; 3.equinox. (b) Outline three effects of the revolution of the earth

Answer Details

(a) Explanation of terms

1. Rotation of the earth: This is the spinning of the earth on its own axis from west to east. The axis is an imaginary line drawn through the North and South Poles, inclined at \(66\tfrac{1}{2}^\circ\) to the plane of the earth's orbit (or \(23\tfrac{1}{2}^\circ\) from the vertical). One complete rotation takes about 24 hours and gives rise to day and night.
2. Revolution of the earth: This is the movement of the earth in its orbit around the sun. The earth completes one revolution in about \(365\tfrac{1}{4}\) days (one year), moving in an elliptical path while its axis remains tilted and pointing in the same direction (parallelism of the axis).
3. Equinox: This is the time, occurring twice a year (around 21 March and 23 September), when the sun is overhead at the equator and day and night are of equal length (12 hours each) all over the world. The word means "equal night".

(b) Three effects of the revolution of the earth

• It causes the seasons of the year (spring, summer, autumn and winter) because of the changing position of the earth relative to the sun combined with the tilt of the axis.
• It causes varying lengths of day and night at different times of the year, especially away from the equator.
• It causes the apparent migration of the overhead sun between the Tropic of Cancer and the Tropic of Capricorn, and forms the basis of the calendar year of about \(365\tfrac{1}{4}\) days, which necessitates a leap year.