Equinox (astronomical event)

An equinox is an astronomical event that occurs twice a year when the Sun's position is directly above the Earth's equator. This results in nearly equal daylight and nighttime hours worldwide. The vernal equinox marks the beginning of spring, usually around March 20-21, while the autumnal equinox signals the start of fall, around September 22-23. These events happen because of Earth's axial tilt and its orbit around the Sun, causing the Sun to appear at the same altitude at noon on the equinox days. Equinoxes are important for calendar systems and seasonal changes.