Air insolation Solar radiation is the transfer of energy in the form of electromagnetic waves emitted by the sun . While insolation is part of the solar radiation that reaches the earth's surface . Factors that affect insolation : 1 . Constant influence of the sun The average magnitude of 1.94 cal/cm2/menit actual changes, primarily due to : a) The change in the intensity of solar radiation caused by changes in the number of sun spots , which range from 1 % -2 % . b ) Changes in the Earth - sun distance . This is because the elliptical orbit of the earth and the sun is at the fire . Farthest distance occurred on July 4 ( aphelium ) 151 900 000 km and the closest distance at January 3 ( perihelium ) 149 500 000 km . amount of solar energy received is inversely proportional to the square of the distance . 2 . Effect of the angle of incidence of sunlight Differences in sun angle causes : a) Differences horizontal surface area that gets light . Beam that spans a narrow horizontal...