Tomb-Sweeping Day, that day.

There was no Gregorian calendar in ancient China, but there was a solar calendar. Tomb-Sweeping Day was originally calculated according to the solar calendar in the lunar calendar (the 24 solar terms in the lunar calendar belong to the solar calendar). First of all, the lunar calendar is not a simple lunar calendar, but a combination of yin and yang. So there was a solar calendar in ancient China, which was the twenty-four solar terms. In BC 104, taichu calendar written by Deng officially listed the 24 solar terms in the calendar, and defined their positions. The twenty-four solar terms are formulated according to the laws of the sun's movement (in fact, the laws of the earth's revolution). So it belongs to the solar calendar. You know, this solar calendar is the most accurate calendar known in the world that reflects the laws of the sun. The Gregorian calendar (Gregorian calendar) is also a solar calendar. So it seems to be "calculated by the Gregorian calendar". In fact, the 24 solar terms respond to the seasons more accurately. Each solar term has a fixed position in the earth's orbit. Every minute is not bad. The Gregorian calendar will have an error of one or two days before and after leap years.

The first thing that can be determined is the "two solstices", namely the winter solstices and the summer solstices. The sun reaches the tropic of Capricorn from the winter solstice, and the daytime is the shortest; The sun shines directly on the Tropic of Cancer from summer solstice, and the night is the shortest. Winter solstice and summer solstice are easier to measure. The longest day in a year is the winter solstice, and the shortest is the summer solstice. It is stipulated that the time from the winter solstice to the next winter solstice is one year (the year of the tropic of cancer). A year is divided into twenty-four "qi", which is called twenty-four solar terms. At that time, due to the lack of astronomical knowledge, the flat gas was divided equally by time. From the solstice of winter, there is air every once in a while, such as cold, rain, vernal equinox and so on. , called gas; The other 12 species, such as: slight cold, beginning of spring, fright, etc. , are called solar terms. After the constitutional calendar of the Qing Dynasty, the sun moved on the ecliptic as a solar term or neutral gas 15 degrees.

"Chronicle of Jingchu's Age" said: "On the 150 th day of last winter festival, there was a flurry of rain, which was called three days of cold food without fire." In other words, there is a gap of 105 days from winter solstice to cold food. The Cold Food Festival, also known as "No Smoking Festival", "Cold Food Festival" and "Hundred Fifth Festival", is the 105th day from summer to the future, one or two days before Tomb-Sweeping Day. In other words, Qingming is between 106 and 107 from the winter solstice. One return is 365.438+079 days. Divide the tropical year by 24 and multiply it by 7, and the Qingming time before the constitutional calendar of the Qing Dynasty is about 106.5 days, which is consistent with the Qingming record between the winter solstice 106- 107 days. However, according to the actual data in recent two years, the distance from the winter solstice in modern Tomb-Sweeping Day is 104. 1, but it is before the cold food.

For example, Tomb-Sweeping Day on 20 10 falls on April 5th of the Gregorian calendar (now Gregorian calendar), and the Cold Food Festival falls on April 6th of the Gregorian calendar.