Why are the dates of the 24 solar terms in China generally defined by the solar calendar? For example, the summer solstice is June 2 122 in the solar calendar.

Because the lunar calendar is a lunar calendar, with the full moon as the month and the earth orbiting the sun as the year, giving consideration to both ends, resulting in the phenomenon of nine leaps in seventeen years, so the month and day of each year are not fixed, so we should rely more professionally on the lunar calendar to find solar terms. The solar calendar is relatively fixed, so the solar terms are also relatively fixed, that is, the first half of the year starts from June 2 1 day, and the second half starts from August 23, and the two festivals remain unchanged every month, with a maximum difference of one or two days.