A solstice is one of two days each year when the sun reaches its highest or lowest point in the sky, creating either the longest day or the longest night.

The summer solstice happens around June 21 in the Northern Hemisphere. On this day, the sun stays up longer than any other day of the year, giving maximum daylight for outdoor activities. Meanwhile, people in the Southern Hemisphere experience their winter solstice, their shortest day. Six months later, around December 21, the roles reverse: the Northern Hemisphere gets its shortest day while the Southern Hemisphere enjoys its longest.

Ancient civilizations tracked solstices carefully. Stonehenge in England was built to align with the summer solstice sunrise. The Inca held major festivals during the winter solstice. Many cultures still celebrate these turning points in the year's cycle.

After each solstice, the days gradually shift in the other direction. Following the winter solstice, each day gets a little longer until summer. After the summer solstice, nights slowly lengthen until winter returns. In many places, these astronomical events are used to mark the official beginnings of summer and winter.