First day of summer. The exact time when the sun reaches its northern-most point (stops moving north), and begins heading back south is ยป 23:59 UTC (Greenwich Mean).
If you live here on the Left coast (like me) that would put the beginning of summer at (-7 hours) 4:59 PM .. if my math is correct.
For our friends who live south of the equator, today's the first day of winter. Don't worry .. we'll send the sun back your way (after we're done playing at the beach for a few months).
Today is the longest day of the year. Starting today, the days begin to shorten .. a few minutes every day. The word solstice means "sun stoppage," cuz it appears as if the sun stops moving for a few days. From InfoPlease:
For several days before and after each solstice the sun appears to stand still in the sky, i.e., its noontime elevation does not seem to change from day to day.