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See chart below to see the exact dates and times for the first day of each season in 2013—namely, the summer solstice, fall or autumnal equinox, winter solstice, and spring or vernal equinox.
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.
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The first day of summer—the summer solstice [3]—is the longest day of the year, the Sun reaches its most northern point in the sky at local noon. After this date, the days start getting shorter. See our First Day of Summer page [3]!
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On the first day of fall—the autumnal equinox [4]—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 [4]!
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The start of winter—the winter solstice [5]—is the shortest day of the year, when the Sun reaches its most southern point in the sky at local noon. After this date, the days start getting longer. See our First Day of Winter page [5]!
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On the first day of spring—the vernal equinox [6]—day and night are each approximately 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days before the vernal equinox). The Sun crosses the celestial equator going northward; it rises exactly due east and sets exactly due west. See our First Day of Spring page [6]!
Credit: NASASeasons of 2013: SPRING EQUINOX March 20, 7:02 A.M. EDT SUMMER SOLSTICE June 21, 1:04 A.M. EDT FALL EQUINOX September 22, 4:44 P.M. EDT WINTER SOLSTICE December 21, 12:11 P.M. EST Seasons of 2014: SPRING EQUINOX March 20, 12:57 P.M. EDT SUMMER SOLSTICE June 21, 6:51 A.M. EDT FALL EQUINOX September 22, 10:29 P.M. EDT WINTER SOLSTICE December 21, 6:03 P.M. EST -
