It stands to reason that it takes the same time for the earth to make a revolution, and the date of reaching the autumnal equinox is the same. However, because the time required by human beings is different from that required by the earth's actual revolution, the earth passes through the autumnal equinox twice, which is equivalent to a revolution. Our calendar shows that it takes 365 days, but the actual time on earth is 365.256 days. In order to eliminate the error, mankind introduced the leap year method, with a leap year of four years and a leap year of 3600 years.
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The vernal equinox usually refers to the moment when the sun's ecliptic is at 0, which is around February 15 of the lunar calendar every year (about March 20 to 2 1 in the Gregorian calendar).
Summer solstice is one of the 24 solar terms, which occurs on June 20th, or 2 1, or 22nd of the Gregorian calendar every year. On the day of summer solstice, the sun moves to 90 degrees of the yellow meridian (summer solstice, currently in Gemini), and the position where the sun directly hits the ground reaches the northernmost point of the year, almost directly to the Tropic of Cancer. At this time, the daylight hours in all parts of the northern hemisphere reach 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 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). After the autumnal equinox, the direct point of the sun continued to move from the equator to the southern hemisphere, and the days in the northern hemisphere began to shorten and the nights became longer, that is, the days in a day began to be shorter than the nights; The southern hemisphere is the opposite. Therefore, the autumnal equinox is also called the landing point.
Winter solstice, commonly known as "Winter Festival", "Dragon solstice Festival" or "Children's Day". The solstice in winter has both natural and humanistic connotations. It is not only an important solar term among the 24 solar terms, but also a traditional festival of the Chinese nation. The solstice in winter is considered as a big holiday in winter. In ancient times, there was a saying that the winter solstice was as big as a year. In ancient times, people wandering in other places had to go home for the winter festival at this time, which was called "having a home at the end of the year". In many areas, there are customs such as ancestor worship in winter solstice, and some places celebrate this festival in winter solstice.