A solstice occurs when the Sun reaches its northernmost or southernmost point in the sky relative to Earth's equator, creating the year's longest and shortest days. This astronomical event happens because Earth tilts 23.5 degrees on its axis as it orbits the Sun, causing different hemispheres to receive varying amounts of sunlight throughout the year.</p><p>The summer solstice (around June 21) marks the longest day in the Northern Hemisphere, when the Sun appears highest in the sky and daylight can last over 16 hours in many locations. Conversely, the winter solstice (around December 21) brings the shortest day, with some northern regions experiencing fewer than 8 hours of daylight. The Southern Hemisphere experiences opposite seasons during these same dates.</p><p>Ancient civilizations recognized solstices long before understanding their cause. Stonehenge in England, built around 2500 BCE, precisely aligns with the summer solstice sunrise, demonstrating early astronomical knowledge. Many cultures celebrated these turning points—Romans held Saturnalia during winter solstice, while modern Scandinavian Midsummer festivals honor the summer solstice.</p><p>Solstices mark crucial seasonal transitions, affecting everything from agriculture to animal migration patterns. They occur exactly twice yearly when the Sun's path across the sky reaches its extreme northern or southern positions, making them fundamental reference points in our calendar system.