Why is Tomb-Sweeping Day not a fixed date of the lunar calendar?

Qingming is usually between April 4 and June in the solar calendar, but it cannot be based on the determined lunar date. Because the number of days in the lunar calendar is different from that in the solar calendar.

The lunar calendar in astronomy mainly refers to the calendar arranged according to the moon phase cycle. The calendar of the moon's one-week orbit around the earth (taking the sun as the reference object, the actual moon's orbit is more than one week) is January, that is, the first month of the lunar calendar is used as the basis for determining the calendar month, and a year is twelve calendar months. In the process of calendar development and evolution, the emergence of 24 solar terms was used to scientifically guide agricultural production, and the lunar calendar (Han calendar) was formed. Although the lunar calendar and lunar calendar are commonly known as lunar calendar, ancient calendar, Han calendar, summer calendar and old calendar, there are differences between lunar calendar and lunar calendar (Han calendar). The traditional summer calendar (Han calendar) is actually a kind of yin-yang calendar. On the contrary, the Islamic calendar is a pure lunar calendar.

Lunar calendar is one of the traditional calendars in China, which is also called lunar calendar, ancient calendar, Han calendar, yellow calendar, summer calendar and old calendar. Many people always think that the lunar calendar is the lunar calendar (Chinese calendar), but it is not. The lunar calendar (Han calendar) is a combination of yin and yang calendars and leap months, and there is no leap month in the lunar calendar.

The lunar calendar determines the moon according to the law of its movement: the orbit of the moon is called the white road, and both the white road and the ecliptic are two great circles on the celestial body, which intersect at five degrees and nine minutes. The moon goes around the earth and appears on the ecliptic twice, which lasts for 7 hours and 43 minutes 1 1.5 seconds on the 27th, and is called "Stellar Moon". Only when the moon revolves around the earth, the position of the earth also changes. The forward count is more than 27 degrees, and the moon runs 13 degrees 15 minutes every day, so it takes 12: 44: 2.8 to return to the moon on the 29th, which is called "the first moon", and it is called the moon according to custom, which means the first moon.