Question

You know that the Sun is the source of heat on the Earth. But why do you think the heat varies from morning to night or from season to season and from place to place? We are listing some variations here. Try to think a reason for it and discuss in the class before you proceed to read this chapter.

1. Cool in the early morning and warmer in the afternoon. 

2. Warm in summer and cool in winter. 

3. Cool on hill tops and warm in the plains. 

4. Warm in Equatorial region and cold in Polar region.

Answer 1

The heat on the earth varies from morning to night or from season to season and from place to place. The reasons are latitude, altitude, distance from the sea, ocean currents, mountain barriers, air masses and prevailing wind system.

Reason 1: 

In the morning the Sun’s rays are slanting on a particular place. In the afternoon they are straight on the same place. This is due to rotation.

Reason 2: 

During the summer the Sun’s rays hit the earth at a steep angle. The light does not spread out as much, thus increasing the amount of energy hitting any given spot. Also the long day light hours allow the earth plenty of time to reach warm temperatures. This is due to revolution. 

Reason 3: 

The average rate of decrease of the temperature of normal air with the increase in height. It is equal to 6°C/km. (Normal Lapse Rate) 

Reason 4: 

The Sun’s rays fall straight on the equatorial region and starting on the poles. This is due to curvature of the earth.