The equinox occurs when the sun is directly above the Earth's equator, resulting in nearly equal day and night durations worldwide. This event happens twice a year, marking the change of seasons. The Vernal Equinox around March 20–21 signals the start of spring, while the Autumnal Equinox around September 22–23 marks the beginning of autumn. On these days, day and night are approximately 12 hours each everywhere on Earth.