What does the "autumnal equinox" mean on the calendar? Please help me explain, thank you!

The so-called autumnal equinox is the equal division of autumn, that is, the autumn is over half. On this day (and the vernal equinox), the length of day and night is equal, and the later the night, the longer it will be until the winter solstice reaches the longest!

Geographically speaking, at the autumnal equinox (and vernal equinox), the sun shines directly at the equator, and the north and south poles are illuminated by the sun at the same time. After this day, the direct point of the sun began to move from the equator to the southern hemisphere, and the southern hemisphere entered the summer half year and the northern hemisphere entered the winter half year. The South Pole will gradually be illuminated by the sun until the extreme day, and the North Pole will gradually enter the extreme night.

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