The earth is revolving around the sun in an elliptical orbit, resulting continuous change in the distance between sun and the earth on annual basis. It leads to seasonal variation in solar energy received by the earth.The mean distance between the earth and sun is about 149,600,000 kilometers(92,900,000 miles).When earth position is farthest(152 million km) from sun is known as ‘aphelion’ on July 4. It is perihelion(147 million km)occurs on January 3 each year which is the closest distance. During aphelion the northern hemisphere is facing the sun and therefore receives energy about 7 percent less than the perihelion (southern hemisphere).