Solar terms, the sun position of the earth

During the summer solstice, the direct sunlight on the ground reaches the northernmost part of the year, almost directly reaching the Tropic of Cancer. At this time, the daylight time in the northern hemisphere reaches the longest in the whole year. For the Tropic of Cancer and its northern area, the summer solstice is also the highest day of the year at noon. On this day, the northern hemisphere received the most solar radiation, almost twice as much as the southern hemisphere.

The solstice in winter is just the opposite of the solstice in summer. The position where the sun shines directly on the ground reaches the southernmost point of the year, almost directly on the tropic of Capricorn. At this time, the daylight hours in all parts of the southern hemisphere reach the longest in the whole year. For the Tropic of Capricorn and its south, the winter solstice is also the highest day of the year at noon. On this day, the southern hemisphere received the most solar radiation, almost twice as much as the northern hemisphere. This is why, in winter, China is very cold, and some people go to countries in the southern hemisphere (such as Brazil and Australia) for the summer.

The autumnal equinox, the sixteenth solar term in the twenty-four solar terms of the lunar calendar, usually falls from September 22nd to 24th in the Gregorian calendar every year. The climate in the south began to decline from this solar term. First, the sun arrived at 180 (autumnal equinox) on this day, and the sun almost directly hit the equator of the earth, and the length of day and night is equal all over the world (regardless of the refraction of sunlight by the atmosphere and the shadow in the morning).

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.