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Equinox and Solstice |
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A solstice is either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days. In the northern hemisphere, the summer solstice corresponds to the longest day (daylight hours) of the year while the winter solstice corresponds to the shortest day of the year. The summer solstice marks the first day of the summer season about June 21 while the winter solstice marks the first day of the winter season about December 21. An equinox (twice each year) is when the sun crosses the celestial equator and the day and night are of equal length all over the world (the number of hours of daylight versus the number of hours of nighttime). All over the world, the vernal or spring equinox occurs on about March 21 while the autumnal equinox occurs on about September 22.
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There are 365 day in one year. The number of days from March 21 to September 21 (that is, the number of days in the combined seasons of spring and summer) is 185 days (including March 21 but excluding September 22), while the number of days from September 22 to March 20 (that is, the number days in the combined seasons of autumn/fall and winter) is 180 days (including September 22 but excluding March 21). Why the difference? Why aren’t the number of days between the two equinoxes the same? They would be if the earth’s orbit around the sun was circular, but the earth’s orbit is not circular, it is elliptical (oval). So, the spring/summer period is 5 days longer than the fall/winter period (seasons for the northern hemisphere). Winter in the northern hemisphere is shorter (89 days) than summer (94 days) and the winter season is colder than the summer season even though the earth is closer to the sun in the winter than in the summer.
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