June 21st, the summer solstice, is
the longest day of the year (about 14 hours in Tucson). Days
start getting shorter the day after the summer solstice. On Sep.
21 (give or take a day or two) the days are 12 hours long. They
continue getting shorter until Dec. 21, the winter solstice and the
shortest day of the year (about 10 hours in Tucson). Then days
start getting longer again.