Liu Heng talks about solar terms.

In fact, strictly speaking, the 24 solar terms are not calculated according to the lunar calendar or solar calendar, but are divided into 24 parts according to the 360-degree rotation of the earth around the sun, and each part is a solar term. The solar calendar is also based on how many days and nights it takes for the earth to orbit the sun 360 degrees. A circle around the sun is not exactly 365 days and nights, so there is a leap year, so the 24 solar terms are not a fixed day in the solar calendar, but one of two adjacent days.

Generally speaking, the twenty-four solar terms and the solar calendar are calculated according to the rotation of the earth around the sun, so they are quite consistent with the solar calendar, while the lunar calendar is calculated according to the rotation of the moon around the earth, so the fifteenth day of each month must be a full moon, which has nothing to do with the twenty-four solar terms.