Are the 24 solar terms of the lunar calendar fixed every year?

The twenty-four solar terms are part of the lunar calendar.

Twenty-four solar terms are fixed positions of the yellow meridian, which have no corresponding relationship with the lunar calendar date, and are basically consistent with the Gregorian calendar, but have fluctuations of 1-2 days.

But the lunar calendar is not a lunar calendar, but a yin-yang calendar. The so-called lunar calendar is a calendar that can reflect the changes of both the phases of the moon and the tropic of cancer. This is why the lunar calendar needs to be adjusted according to leap months, so that the average of lunar years can reflect the tropic year.

The twenty-four solar terms are essentially 24 fixed positions of the sun's apparent motion on the ecliptic (the ecliptic is divided into 24 points, each of which is 15). The four most important ones are: vernal equinox (longitude 0, day and night equally divided), summer solstice (longitude 90, the shortest shadow and the longest day), autumn equinox (longitude 180, day and night equally divided) and winter solstice (longitude 270, the longest shadow and the longest night).

After observing the bisection, you can calculate the rest of the solar terms. So the interval of each solar term is roughly 365/24= 15 days (in fact, the revolution of the earth is not uniform, so it is not a simple division). But solar terms are precise longitude, so solar terms are actually precise time, not a day. It just means that the solar term falls on a certain day, which is called the solar term.

By the way, the leap of the lunar calendar is based on the 24 solar terms.

The Gregorian calendar is a solar calendar, which does not reflect the phase of the moon, but only the tropic year. Therefore, the Gregorian calendar and the 24 solar terms can be well matched. But because the interval between the two solar terms is not exactly 15 days, and the Gregorian calendar itself is not evenly distributed every month. So there will be a fluctuation of 1-2 days. That is, as the twenty-four solar terms Song said: the first half of the year is June 21st; The second half of the year is August 23rd. The two festivals remain unchanged every month, with a maximum difference of one or two days.