Periods according to time of equation and astronomical seasons. During X1(February 11-May 04) and X2 (July 26-November 03) (marked with pink lines) sun time is accelerating, and during Y1 (May 15-July25) and Y2 (November 04-February 10) (marked with green lines) it is decelerating compared with the coordinated universal time (UCT). During A1 (April 15-June13) and A2 (September 01-December 25) sun time stays ahead and during D1 (June 14-August 31) and D2 (December 26-April 14) it stays behind the UCT. Astronomical seasons are separated with dotted vertical lines. During astronomical spring and summer daylight exceeds darkness, and vice versa during astronomical fall and winter darkness exceeds daylight in Finland. Y-axis on the left side presents the time difference (in minutes) that sun time deviates from the UCT.