Solar radiation is the term used to describe the radiant energy given off as a result of nuclear fusion reactions occurring in the Sun. Pyranometer and Pyrheliometer are the commonly used methods of measuring solar radiation. Solar radiation is visibly present during the day when the sun is most visible during the day as well as in summer at night near the poles. Solar radiation is not visible during winters near the poles as direct radiation is blocked by clouds. Solar radiation is experienced as sunshine which is the grouping of the perceived white light that is sunlight and the warming due to sunlight. The increase in atmospheric temperature due to sunshine helps to distinguish between the warming of surfaces of different bodies. Mathematically, the amount of solar radiation trapped by a planet is inversely proportional to the square of the total distance between the solar body emitting radiation and the planet.

The earth’s orbit and its fixed position changes in the span of thousands of years and at times also forms an almost complete circle while at other times, the earth stretches into an orbital eccentricity. Even though the total insolation or thermic fever remains almost same throughout but the Earth’s seasonal, latitudinal as well as the distribution of solar radiation received varies. Such changes in winter and summer tend to disturb, the overall annual insolation which at all locations is almost zero, but due to the redistribution of solar radiation between winters and summers causes variance in intensity of seasons.