Solstice

A solstice is an astronomical event that occurs twice each year (in June and December) as the Sun reaches its highest or lowest excursion relative to the celestial equator on the celestial sphere. Both the solstices and the equinoxes are directly connected with the seasons of the year.

The term solstice can also be used in a broader sense, as the day when this occurs. The day of the solstice is either the longest day of the year (summer solstice) or the shortest day of the year (winter solstice) for any place outside of the tropics. Alternative terms, with no ambiguity as to which hemisphere is the context, are June solstice and December solstice, referring to the months of year in which they take place.

At latitudes in the temperate zone, the summer solstice marks the day when the sun appears highest in the sky. However, in the tropics, the sun appears directly overhead (called the subsolar point) some days (or even months) before the solstice and again after the solstice, which means the subsolar point occurs twice each year.