English: The durations of the seasons. The season lengths are different because Orbital mechanics require that the length of the seasons be proportional to the areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can be substantially longer in duration. Today, when fall and winter occur at closest approach, the earth is moving at its maximum velocity and therefore fall and winter are slightly shorter than spring and summer. Today, summer is 4.66 days longer than winter and spring is 2.9 days longer than fall.