Solstice
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Solstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. The name is derived from Latin solstitium (from sol: "sun" and sistere: "stand still"). During the year, the position of the sun seen from earth moves North and South. When it changes direction it stands still momentarily. So 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.
The solstice is related to the axial tilt of the planet. 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 most other solar system 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.
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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 North pole the sun circles the sky at a constant altitude of 23°.
At the Polar Arctic Circle the middle of the sun just grazes the horizon due North without setting. It reaches its maximum altitude of 47° in the South. This is the only day of the year that the sun stays above the horizon for 24 hours.
At the Tropic of Cancer the sun rises about 26° North of East. It reaches its maximum altitude at the zenith. It sets about 26° North of West. The sun stays above the horizon for 13.4 hours.
At the equator the sun rises about 23° North of East. It reaches its maximum altitude of 67° in the North. It sets about 23° North of West. The sun stays above the horizon for 12 hours.
At the Tropic of Capricorn the sun rises about 26° North of East. It reaches its maximum altitude of 43° in the North. It sets about 26° North of West. The sun stays above the horizon for 10.6 hours.
At the Polar Antarctic Circle the middle of the sun just grazes the horizon due North without rising. This is the only day of the year that the sun does not rise above the horizon.
At the South pole the sun never rises, always staying 23° below the horizon.
December solstice
At the North pole the sun never rises, always staying 23° below the horizon.
At the Polar Arctic Circle the middle of the sun just grazes the horizon due South without rising. This is the only day of the year that the sun does not rise above the horizon.
At the Tropic of Cancer the sun rises about 26° South of East. It reaches its maximum altitude of 43° in the South. It sets about 26° South of West. The sun stays above the horizon for 10.6 hours.
At the equator the sun rises about 23° South of East. It reaches its maximum altitude of 67° in the South. It sets about 23° South of West. The sun stays above the horizon for 12 hours.
At the Tropic of Capricorn the sun rises about 26° South of East. It reaches its maximum altitude at the zenith. It sets about 26° South of West. The sun stays above the horizon for 13.4 hours.
At the Polar Antarctic Circle the middle of the sun just grazes the horizon due South without setting. It reaches its maximum altitude of 47° in the North. This is the only day of the year that the sun stays above the horizon for 24 hours.
At the South pole the sun circles the sky at a constant altitude of 23°.
See also
External links
- Solstice Dates and Times (http://www.islandnet.com/~see/weather/almanac/seasondate.htm)da:Solhverv
de:Sonnenwende (Astronomie) eo:Solstico fr:Solstice it:Solstizio nl:Zonnewende pl:Przesilenie sl:Sončev obrat