Summer solstice
The summer solstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. The summer solstice is the date with the longest day and hence with the shortest night. This date usually falls on June 21/June 22 (in the Northern hemisphere) or December 21/December 22 (in the Southern hemisphere).At the time of this solstice, the earth is in that point of its orbit at which the hemisphere in question is most tilted towards the sun, causing the sun to appear at its farthest above the celestial equator when viewed from earth.
Midsummer is the time around the summer solstice. There are traditional holidays celebrated in Northern Europe and elsewhere at this time. In Denmark midsummers eve is know as Sankt Hans Aften. Bonfires are lit on beaches throughout the land as darkness comes and mock witches and fireworks are thrown into the fires. It is also a sabbat of Neopaganism.
In the USA the summer solstice is regarded as the start of summer.