The summer solstice occurs June 20 or June 21 for the earth north of the equator. The seasonal significance of the Summer solstice is in the reversal of the gradual shortening of nights and lengthening of days and is better known as the First Day Of Summer.
Solstice is derived from a combination of Latin words sol (sun) and sistere (to stand still). As the days lengthen, the sun rises higher and higher until it seems to stand still in the sky.
One of the most modern ties with Summer Solstice were the Druids' celebration of the day as the wedding of Heaven and Earth, resulting in the present day belief of a "lucky" wedding in June.
For a full explanation of the summer solstice visit: