• The Factors influencing the Amount of insolation received by different parts of the earth are the:

(i) the rotation of earth on its axis

(ii) the angle of inclination of the sun’s rays 

(iii) the length of the day

(iv) the transparency of the atmosphere

(v) the configuration of land in terms of its aspect

The rotation of earth on its axis

• The earth’s axis makes an angle of 66½ with the plane of its orbit around the sun.
• This inclination of earth’s axis has a greater influence on the amount of insolation received at different latitudes

The angle of inclination of the sun’s rays

• The angle of the sun’s rays is nearly perpendicular at Noon. So the rays get concentrated over a small area and give more heat.
• When the angle of incidence is high, the area affected is small and insolation and is concentrated on a smaller area, hence the heat received per unit area is large and heated to a higher degree.
• The angle of incidence of the sunrays is oblique during morning and evening, therefore they spread over a large area and hence the heating effect is less.
• The high angle of incidence means that the length of the path of the insolation rays through the atmosphere is shortest, and it loses only a small amount of its heat through absorption, scattering, and reflection.
• When the angle of incidence is smaller, the area affected is larger and the heat per unit of area is much less. At the same time, the longer path through the atmosphere results in a larger amount of loss of heat.
• The sun’s rays are more direct in summer than in winter. 
• The angle of the sun’s rays also varies with latitude. The angle of the sunray is vertical at the lower latitudes and as we go towards the poles, the sunrays are more oblique.

Duration of the day

• During summer, days are longer and nights are shorter. During winter, nights are longer and days are shorter.
• The amount of insolation is higher during summer than in winter.  

The transparency of the atmosphere

• The atmosphere is largely transparent to shortwave solar radiation. 
• Within the troposphere water vapour, ozone and other gases absorb much of the near infrared radiation.
• Very small-suspended particles in the troposphere scatter visible spectrum both to space and towards the earth surface. 
• This process adds colour to the sky. The red colour of the rising and the setting sun and the blue colour of the sky are the result of scattering of light within the atmosphere.