Science Fact Finder | Time, Weights, and Measures - Why Are The Lengths Of The Seasons Not Equal?

Why are the lengths of the seasons not equal?

The lengths of the seasons are not exactly equal because the shape of the Earth's orbit around the sun is elliptical (oval) rather than circular. And the sun is not at the center (lengthwise) of the ellipse—to the contrary, the sun is closer to one end of the ellipse than to the other.

When the Earth is closest to the sun in January, gravitational forces cause the Earth to move faster than it does in the summer months, when it is farther away from the sun. As a result, fall and winter seasons in the Northern Hemisphere (the half of the Earth north of the equator) are slightly shorter than spring and summer. Spring and summer are shorter than fall and winter in the Southern Hemisphere. The duration of the Northern Hemisphere seasons are as follows:

spring	92.76 days
summer	93.65...

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