The summer solstice occurs when a planet's rotational axis, in either northern or southern hemispheres, is most inclined toward the star that it orbits. Earth's maximum axial tilt toward the Sun is 23° 26′. This happens twice each year (once in each hemisphere), at which times the Sun reaches its highest position in the sky as seen from the north or the south pole.
The summer solstice occurs during a hemisphere's summer. This is the northern solstice in the northern hemisphere and the southern solstice in the southern hemisphere. Depending on the shift of the calendar, the summer solstice occurs some time between June 20 and June 22 in the northern hemisphere and between December 20 and December 23 each year in the southern hemisphere. The same dates in the opposite hemisphere are referred to as the winter solstice.
When on a geographic pole, the Sun reaches its greatest height, the moment of solstice, it can be noon only along that longitude which at that moment lies in the direction of the Sun from the pole. For other longitudes, it is not noon. Noon has either passed or has yet to come. Hence the notion of a solstice day is useful. The term is colloquially used like midsummer to refer to the day on which solstice occurs. The summer solstice day has the longest period of daylight – except in the polar regions, where daylight is continuous, from a few days to six months around the summer solstice.
2016 was the first time in nearly 70 years that a full moon and the summer solstice concur on the same day. The 2016 summer solstice's full moon will rise just as the Sun sets. The moment of the full moon is early Monday on June 20.
Worldwide, interpretation of the event has varied among cultures, but most recognize the event in some way with holidays, festivals, and rituals around that time with themes of religion or fertility.
Solstice is derived from the Latin words sol (sun) and sistere (to stand still).
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