When Do Fall, Winter, Spring, and Summer Begin?
See chart below for exact dates and times for the first day of each season in 2013—namely, the fall or autumnal equinox, winter solstice, spring or vernal equinox, and summer solstice.
Why do the seasons change? The four seasons are determined by shifting sunlight (not heat!)—which is determined by how our planet orbits the Sun and the tilt of its axis.
On the first day of fall—the autumnal equinox—day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after the autumnal equinox). The Sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west. See our First Day of Fall page!
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