The greatest seasonal contrast of insolation is seen in polar zone due to the inclination of 23.5 degrees of the earth's rotation axis with respect to its orbital axis. Sun rays are directly overhead on Tropic of Cancer during the month of June and on Tropic of Capricorn during the month of December. Poles experience 24 hour days during summer and 24 hour nights during winters, thus experiencing maximum variation among all the regions on earth.