Solstice
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, and not the Solar apsides (aphelion and perihelion) of the planet, as many people commonly believe. In other words, solstices are artifacts of the Tropical year, not the anomalistic year.
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 dates of the Winter Solstice and Summer Solstice are reversed for the northern and southern hemispheres.
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 sun touches the horizon at North without setting.
At the Polar Antarctic Circle the sun 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 sun touches the horizon at South without rising.
At the Polar Antarctic Circle the sun touches the horizon at South 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'.