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Solstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. It is related to the axial tilt of the planet. Solstices are those moments of the year when the sun reaches its southernmost or northernmost position, at the Celestial Tropic of Capricorn or Celestial Tropic of Cancer, respectively.
A common misconception is that the Solstice occurs at the Solar apsides (aphelion and perihelion) of the planetary orbit. Since the orbital eccentricity of the earth (and all solar planets) is close to zero, the orbit is nearly circular. Therefore, the amount of sunlight received for the earth as a whole is nearly the same throughout the year. Seasons are, incidentally, caused by the tilt of the earth, which causes one hemisphere to receive more solar energy each day, at the expense of solar energy received by the other hemisphere. The solstices mark the points of greatest imbalance in energy received by the different hemispheres.
The dates of the Winter Solstice and Summer Solstice are reversed for the northern and southern hemispheres. The dates of the solstices in the most widely used Gregorian calendar shift in a regular pattern (see Gregorian_calendar#Calendar_seasonal_error).
Solstice festivals were common (and held primacy) in most cultures of the ancient world.
Behaviour of the sun
On the solstices the length of the day and the altitude of the sun at noon are the maximum or the minimum of all the other days of the year.
June solstice At the equator the sun rises about 24° left from the East. Then it passes from North, where it reaches its maximum altitude of that day, that is 66°33'. Then it sets about 24° right from the West.
At the Tropic of Cancer the sun rises about 26° left from the East. Then it passes from the zenith. Then it sets about 26° right from the West.
At the Tropic of Capricorn the sun rises about 26° left from the East. Then it passes from the North, where it reaches its maximum altitude of that day, that is 43°06'. Then it sets about 26° right from the West.
At the Polar Arctic Circle the middle of the sun just touches the horizon at South without setting.
At the Polar Antarctic Circle the middle of the sun just touches the horizon at North without rising.
At the North pole the altitude of the sun is always +23°27'.
At the South pole the altitude of the sun is always -23°27'.
December solstice At the equator the sun rises about 24° right from the East. Then it passes from South, where it reaches its maximum altitude of that day, that is 66°33'. Then it sets about 24° left from the West.
At the Tropic of Cancer the sun rises about 26° right from the East. Then it passes from the South, where it reaches its maximum altitude of that day, that is 43°06'. Then it sets about 26° left from the West.
At the Tropic of Capricorn the sun rises about 26° right from the East. Then it passes from the zenith. Then it sets about 26° left from the West.
At the Polar Arctic Circle the middle of the sun touches the horizon at South without rising.
At the Polar Antarctic Circle the middle of the sun touches the horizon at North without setting.
At the North pole the altitude of the sun is always -23°27'.
At the South pole the altitude of the sun is always +23°27'.
See also
External links - Solstice Dates and Times (http://www.islandnet.com/~see/weather/almanac/seasondate.htm)
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