by Tenebris

Created on: June 15, 2008   Last Updated: April 02, 2009

Regions north of the Tropic of Cancer and south of the Tropic of Capricorn experience seasons as a result of receiving sharply different lengths of daylight at different times of the year. Four special days in the year mark the turning of the seasons: the two solstices at the extremes of daylight and darkness, and the two equinoxes at the time of year when the periods of daylight and darkness are exactly equal. These four days occur at almost exactly three month intervals, and mark the beginning of each new season.

The seasons of the northern and southern hemisphere, and thus which solstice or equinox each hemisphere experiences, are directly opposite each other. When one hemisphere experiences the vernal, or spring, equinox, the other has the autumnal equinox. When one marks the summer solstice, the other descends into the long, cold night of the winter solstice.

The vernal equinox occurs at the beginning of spring, at that time of year when daylight and darkness are exactly equal. For regions north of the Arctic Circle and south of the Antarctic Circle, the sun will have returned at some point before this day: for during the depths of winter, these regions are plunged into constant night; while during the summer, the sun can shine around the clock. The further poleward you go, the longer the hours of summer daylight: until at the poles themselves, the days and nights last six months each, beginning and ending at the equinoxes. In the northern hemisphere, the vernal equinox falls sometime between March 20 and 24, while in the southern hemisphere, it falls sometime between September 20 and 24.

The summer solstice marks the beginning of summer, at that time of year when the daylight is longest. Every region north of the Arctic Circle and south of the Antarctic Circle will experience 24-hour daylight on the summer solstice. In the northern hemisphere, the summer solstice falls sometime between June 20 and 24, while in the southern hemisphere, it falls sometime between December 20 and 24.

As per its name, the autumnal equinox is the harbinger of autumn, falling at the second time of year when daylight and darkness are exactly equal. For regions north of the Arctic Circle and south of the Antarctic Circle, the sun will soon sink for a final time for the winter darkness. The further poleward you go, the longer the night to come: until at the poles themselves, this date marks the beginning of six months of night. In the northern hemisphere, the autumnal equinox falls

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