The autumnal equinox occurs around September 22 or 23 each year, marking the moment when day and night are approximately equal in length. This event happens as the Earth orbits the Sun, causing the Sun to cross the celestial equator from north to south. During the autumnal equinox, many cultures celebrate the changing seasons, often associated with harvest festivals. The equinox signals the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere, influencing weather patterns and natural cycles.