text: what is the day of the year where the sun stays up the longest?   the summer solstice is the longest day of the year, respectively, in the sense that the length of time elapsed between sunrise and sunset on this day is a maximum for the year. of course, daylight saving time means that the first sunday in april has 23 hours and the last sunday in october has 25 hours, but these human meddlings with the calendar and do not correspond to the actual number of daylight hours. in chicago, there are 15:02 hours of daylight on the summer solstice of june 21, 1999.