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seasons
Any of the four climatically different periods of the year that arise because of the tilt of Earth's rotational axis relative to the orbital plane. The fixed tilt means that, at any given location, the altitude of the Sun and the length of daylight hours, changes on an annual cycle. The effects of these differing amounts of solar heating are most pronounced at high latitudes. The four seasons are astronomically defined by the different positions of the Sun with respect to the equator. In the northern hemisphere, spring is measured from the vernal equinox (March 21) to the summer solstice (June 22), summer from the summer solstice to the autumnal equinox (September 23), autumn from the autumnal equinox to the winter solstice (December 22), and winter from the winter solstice to the vernal equinox. In the southern hemisphere, the seasons are reversed.
Related category
• CELESTIAL MECHANICS
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