Solstice literally means ‘standing of the sun’ and the summer solstice occurs when the sun reaches the Tropic of Cancer and the point on the celestial sphere where it is farthest north of the celestial equator, hence giving us our longest day. It takes place in June 21 in the Northern hemisphere and December 21 in the Southern hemisphere.
In Shakespeare’s time June 21 was Midsummer Day/Night. This harks back to a time when the year was divided into two seasons- summer and winter (in fact, the Sanskrit word for summer means ‘half year’), whereas now many dictionaries define summer as actually beginning on June 21.
Although the summer solstice actually occurs around June 21, in Europe Midsummer Day was celebrated on fixed day, June 24, just as the winter solstice was celebrated on December 25 rather than December 21. And just as the birth of Christ was fixed at December 25 to quash the old pagan traditions, John the Baptist’s birthday was fixed on June 24 to detract pagans from worshipping the sun- from the Druids at Stonehenge in England to the Mayans at kukukan pyramid in Mexico.
The ‘fires of St. John’ may have originated in the fertility rites of the Druids. Fires were also lit to encourage the sun not to lose its power and as a cure and protection against disease.
(source: The Book of Days. Cambridge University Press)
A picture of the Summer Solstice in Stonehenge.