The number of daylight hours on a summer day depends upon latitude and can vary from slightly more than 12 hours to a full 24 hours in the northern hemisphere. At any given latitude above the equator, the longest day falls on the summer solstice, which is usually June 21.
The Earth does not face the sun at equal amounts throughout the year because it tilts at an angle of 23.5 degrees. This results in the sun being visible longer in the Northern hemisphere when the North Pole tilts towards it. During the summer solstice, the sun reaches its highest point in the Northern hemisphere's sky and is at its lowest during the winter solstice. The farther north one travels, the longer the day gets. However, the opposite is true at the other pole. When the Arctic Circle experiences 24-hour days, the Antarctic never sees the sun.