The natural phenomenon when day and night are of equal length is called the equinox. There are two equinoxes each year: the vernal equinox in spring and the autumnal equinox in fall. During these times, the Earth's tilt and position relative to the sun result in nearly equal daylight and nighttime hours for most locations on the planet. The equinoxes are significant because they mark the transition between seasons and have been celebrated in various cultures throughout history, often symbolizing balance and renewal.