You might want to stock up on sunscreen. On June 21, 2023, the Northern Hemisphere will experience its longest day of the year, the day when the North Pole is leaning most toward the sun. (This year that takes place at 10:58 A.M. EDT. This annual event is called the summer solstice for those of us in the northern half of the globe — and in addition to the big day's celestial significance, it's a popular time to visit one of the ancient world's greatest relics. Here are five nifty facts about the occasion.