Summer Solstice

In
The Midsummer's Day is an event that happens in the game, it makes no other appearances in the previous games. It happens on the 21st of June in the season of Summer.

This day is supposedly the longest day of the year, the sun set will fall later on this day than any other day. If the player talks to Tortimer, they will receive an Expresso Maker.

In
The Summer Solstice is an event that is in, occurring in the player's town on June 21, the day in which the sun is visible throughout the entire day, even at midnight. When the summer solstice occurs, the town holds a celebration, which is marked by a cut out board featuring a sun and a sunflower. If the player speaks with Isabelle, who is located in the Event Plaza, she will give them a pair of Ladder Shades.

Real Life Definition
The summer solstice occurs when the tilt of a planet's semi-axis, in either the northern or the southern hemisphere, is most inclined toward the star (sun) that it orbits. Earth's maximum axial tilt toward the sun is 23° 26'. This happens twice each year, at which times the sun reaches its highest position in the sky as seen from the north or the south pole. However, what is seen in is actually known in the real world as a "polar day", in which the sun is visible for more than 24 hours, which occurs in the arctic or antarctic circle, during the days near the summer solstice.