Q: Why does the date of the autumnal equinox change from year to year?

Arab Weather - The date of the autumnal equinox changes from one year to another due to the difference in the length of the Gregorian year (365.25 days), and the effect of the leap year, which adds a day every four years. This difference affects the timing of the equinox, making it fall between September 22 and 24.