the Summer Solstice is the beginning of summer. Summer is the season when days are longer than nights, but growing shorter.

The boundaries between seasons are like the boundary between yin and yang on the t'ai chi. There's a little spring in summer and a little summer in spring, and so on.

Also: the days are growing shorter in summer, just as adulthood begins when you begin to age. Aging is the characteristic condition of adulthood, though it's not usually noticeable for the first few years (starting at around 25).

So, for reasons of both astronomy and metaphor, I prefer to think of the solstice as the moment when the world turns to summer. The Sun, in His triumph,

begins His descent into death.

And like that.