Why is every solar term on the same day?

According to the lunar calendar, it should be noted that the lunar calendar in China is a lunar calendar, and there are seven leap months in nineteen years (19 years ago, the Gregorian calendar was the same day or a day later), instead of a simple lunar calendar (Islamic calendar) or a solar calendar (Gregorian calendar also has leap months).

Twenty-four solar terms are divided into twenty-four seasons and climates that reflect the natural phenomena and agricultural characteristics in a certain area of China (represented by the middle and lower reaches of the Yellow River) according to the position of the sun returning to the ecliptic (the route that the sun "walks" through the earth in one year).

The 24 solar terms are calculated according to the lunar calendar. If you simply understand it, you can also understand it according to the solar calendar (western calendar). The days are fixed, but there may be a difference of one or two days every year due to leap months.

In the lunar calendar, the moon orbits the earth 1 month, but a leap month is set, which is consistent with the periodic movement of the moon and the earth around the sun. The "month" in the western calendar has nothing to do with the month.