Why we celebrate the summer solstice (Scientific American)

Today, the Northern Hemisphere celebrates the summer solstice, the longest day of the calendar year (happy winter solstice to the Southern Hemisphere!). Around 1:00AM, the sun was directly above the Tropic of Cancer—and though I was fast asleep at that precise moment, along with most of my fellow East Coasters, I probably woke up earlier than I normally would, and will go to sleep far later. That’s the beauty of the longest day of the year.

But while the day is, technically speaking, an astronomical occasion, its historical and cultural significance extends far beyond the relative length of the daylight. The word solstice itself comes from the Latin, from sol (sun) and stare or sistere (to stand or stop), and its celebration dates back to ancient pre-Christian tradition. For the Greeks, it would, according to some calendars, mark the start of the new year—and the month-long countdown toward the Olympics. It was, too, often the annual occasion for the festival of Kronia, to honor the god Cronus, the patron of agriculture. The day was marked not only by the typical feasts and games, but by an even more remarkable occurrence: for once, slaves could participate in the festivities along with the freemen, joined in equality for a single day.

For the Romans, the solstice was the occasion for another unique exception to everyday life: on the first day of the festival of Vestalia, married women could, for one day only, enter the temples of the vestal virgins. There, they would be allowed to make offerings to Vesta, the goddess of hearth and home.

http://blogs.scientificamerican.com/literally-psyched/2013/06/21/why-we-celebrate-the-summer-solstice/