Front view of vernal equinox and autumnal equinox and top view of North Pole.

Side view of vernal equinox and autumnal equinox

Second, the top view of the North Pole in the Spring and Autumn Period.

First of all, the vernal equinox is the midpoint of 90 days in spring. One of the 24 solar terms, around March 20 of the Gregorian calendar every year, when the sun is located at 0 (vernal equinox) of the yellow meridian. On the vernal equinox, the sun shines directly at the equator of the earth, and the seasons in the northern and southern hemispheres are opposite. The northern hemisphere is the vernal equinox and the southern hemisphere is the autumnal equinox. The vernal equinox is a new year in Iran, Turkey, Afghanistan, Uzbekistan and other countries, with a history of 3,000 years.

Second, the autumnal equinox, the sixteenth solar term in the twenty-four solar terms of the lunar calendar, usually lasts from September 22nd to 24th every year. The climate in the south began to decline from this solar term. First, on this day, the sun reached the longitude of the Yellow River 180 degrees, and directly hit the equator of the earth. Therefore, in most parts of the earth, 24 hours are divided equally, each being 12 hours. Near the North Pole (90 north latitude) and the South Pole (90 south latitude), the special phenomenon that "the sun circles on the horizon all day" can be observed on this day.