Is the real situation in Tomb-Sweeping Day calculated according to the lunar calendar or the solar calendar?

As a traditional solar term in China, Tomb-Sweeping Day is calculated according to the annual vernal equinox, which has a solar term every15th day, so Qingming is between April 4th and 6th in the solar calendar, mostly on the 5th. It is not fixed on April 5 of the solar calendar, nor is it determined by the lunar calendar.

The vernal equinox changes with the rotation of the earth. The earth's rotation in a day is not 24 hours, but 23 hours and 56 minutes, which will decrease by one day every four years, thus affecting the time of solar terms. According to this rule, Tomb-Sweeping Day in 2008 happened on April 4th, 2004 and 2000, while Tomb-Sweeping Day on April 6th was 1939 and 65438+.