In the Northern Hemisphere, the Summer Solstice occurs around June 20 or 21. On this day, the Sun travels its longest path across the sky, resulting in the most daylight hours of the year. Conversely, the Winter Solstice, usually around December 21 or 22, brings the shortest day and longest night, as the Sun follows its lowest and shortest arc through the sky. In the Southern Hemisphere, these events are reversed—summer begins in December, and winter in June.

The word "solstice" comes from the Latin sol (Sun) and sistere (to stand still), referring to the way the Sun appears to pause in its movement before reversing direction. Although solstices mark the official beginning of summer or winter, they don’t necessarily coincide with the warmest or coldest weather, because Earth’s land and oceans take time to heat up or cool down—a phenomenon known as seasonal lag.

Solstices have held deep cultural and spiritual significance throughout human history. Ancient monuments like Stonehenge in England and Newgrange in Ireland were built to align with solstice sunrises or sunsets. The Inca festival Inti Raymi celebrates the winter solstice in Peru, and many winter holidays in the Northern Hemisphere, such as Yule and Christmas, are closely tied to the idea of light returning during the darkest time of the year.

In contrast to solstices, equinoxes occur when day and night are nearly equal in length, but solstices emphasize the extremes: the longest and shortest days. Together, solstices and equinoxes form the framework of Earth’s seasonal cycle, offering a cosmic rhythm that has shaped agriculture, ritual, and human understanding for millennia.