What is the term for the longest day of the year in the Northern Hemisphere?

The term for the longest day of the year in the Northern Hemisphere is the summer solstice.

Astronomically, the summer solstice occurs when Earth’s North Pole is tilted maximally toward the Sun. The Northern Hemisphere then receives its most direct sunlight and experiences its longest period of daylight and shortest night. It is also called the June solstice because it occurs in June.

The event is not caused by Earth being closest to the Sun. Earth’s axial tilt of about 23.44 degrees is the key reason for seasonal changes. At the solstice, the Sun appears directly overhead at the Tropic of Cancer, while locations north of the Arctic Circle can experience the midnight Sun.

The earliest sunrise and latest sunset do not usually occur on the solstice itself; local latitude, time-zone position, and the equation of time shift those moments by several days. The date can also vary: in the Gregorian calendar, the Northern Hemisphere summer solstice generally falls on June 20 or 21. In the Southern Hemisphere, the December solstice is the summer solstice instead.