Today is the first day of astronomical summer, also known as the "longest day of the year" for those of us living north of the equator.

Summer officially began at 12:24 a.m. Philadelphia time, when the sun reached its highest point in the sky as seen from the North Pole.

We will have 15 hours of daylight today, five hours and 45 minutes more than we had during the winter solstice. The amount of daylight will decline gradually until the winter solstice, 11:28 a.m. on Dec. 21.

For meteorologists, summer began June 1, but that date does not attract the same attention as the summer solstice, which has fascinated humans since ancient times. Think of Stonehenge, the scene of solstice festivals for ages.