The position of the direct sunlight at the autumnal equinox.

The sun shines directly on the equator at the autumnal equinox.

The autumnal equinox is the sixteenth of the twenty-four solar terms, and the time is generally from September 22 to September 24 of the Gregorian calendar every year. On the day of the autumnal equinox, the sun reaches the longitude 180 (autumnal equinox), almost reaching the equator of the earth, and the length of day and night is equal all over the world (regardless of the refraction of the sun light by the atmosphere and the shadow in the morning).

The vernal equinox, summer solstice, autumn equinox and winter solstice are the times when the sun directly hits the equator, the tropic of cancer, the equator and the tropic of cancer respectively. Spring, summer, autumn and winter are divided according to the position of the direct point where the sun shines directly on the earth, and the Tropic of Cancer is the northernmost and southernmost point where the sun shines directly on the earth. In other words, direct solar energy is only within the tropic of cancer. The equator just divides it into two parts, one in the northern hemisphere and the other in the southern hemisphere.