Why does Tomb-Sweeping Day change from April 4th to April 6th every year? Thank you for your questions.

Tomb-Sweeping Day, also known as the outing festival, is between April 4th and 6th every year according to the solar calendar, and April 5th every year is not fixed. As for why Tomb-Sweeping Day is not regarded as the lunar calendar, it is actually because Qingming is one of the 24 solar terms in China, and the 24 solar terms are divided according to the position of the sun on the ecliptic (that is, the earth's orbit around the sun). Depending on the sun starting from the vernal equinox (longitude zero, at this moment the sun shines vertically on the equator), every advance of 15 degrees is a solar term; After a week's operation, I returned to the vernal equinox, which is a tropical year with 360 degrees, so it is divided into 24 solar terms. The dates of solar terms are relatively fixed in the solar calendar. For example, beginning of spring in the solar calendar always falls between February 3rd and 5th. However, in the lunar calendar, the date of solar terms is not easy to determine. Take beginning of spring as an example. It can be the first day of the lunar calendar in the previous year, 65438+February 15, and the latest is the first month, 15. Tomb-Sweeping Day is usually between April 4th and June in the Gregorian calendar, but it cannot be based on the determined lunar calendar date. In fact, we can regard the twenty-four solar terms handed down by our ancestors as the solar calendar owned by the Chinese nation, because it is calculated and divided according to the position of the sun on the ecliptic (that is, the orbit of the earth around the sun), and the natural difference is not as great as that of the lunar calendar and the solar calendar. This also reflects the precious scientific heritage of the Chinese nation in astronomy and natural science.

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