There is an old saying in the countryside that "the vernal equinox and the autumnal equinox are equally divided day and night". What does this mean?

Equinox in spring and autumnal equinox, equally divided day and night? This is a seasonal proverb, which means: When the vernal equinox and autumnal equinox come every year, day and night are equal in length, that is, day and night are equally divided, and the climate is moderate. Explain with the knowledge of astronomy that the orbital plane of the earth around the sun has two natural intersections with the celestial sphere (that is, the orbit of the sun on the earth) and the celestial equator, that is, a starting point connecting the 24 solar terms. Equinox? And then what? Autumn equinox? . If the sun moves to these two points, the time between day and night on the earth will be equal, because on this day, the sun shines directly at the equator, but both the southern hemisphere and the northern hemisphere irradiate the same area equally, so the day and night on the earth are equally divided, that is, 12 hour.

At the vernal equinox (that is, when the sun reaches the yellow meridian 0? ) On this day, the solar time just reached the equator. At this time, the terminator line passes through the north and south poles and coincides with the meridian circle of the earth, so all latitudes are divided into two parts, half in the daytime hemisphere and the other half in the nighttime hemisphere, so the global day and night are almost equal.

At the autumnal equinox (that is, the longitude of the sun 180? On this day, the sun went straight to the equator again, and the terminator line also passed through the north and south poles, which coincided with the meridian of the earth and divided all latitudes into two parts. So what? Equinox in spring and autumnal equinox, equally divided day and night? . The difference between them is that after the vernal equinox in the northern hemisphere, the point of direct sunlight will gradually move northward and the solar radiation will gradually increase. At this time, the weather will get warmer, the days will get longer and the nights will get shorter. After the autumnal equinox, the direct point of the sun will gradually move southward, so the radiation of the sun will gradually decrease and the weather will get cold. At the same time, the days will be shorter and the nights will be longer.