Are vernal equinox, summer solstice and autumn solstice fixed?

24 solar terms divided the time of the earth's revolution around the sun into 24 equal periods on average, but the time of the earth's revolution around the sun is not 365 days, and the revolution speed and trajectory will change slightly, so the divided 24 periods are not necessarily in a fixed "day", but will be based on the time point! Can't be understood as a whole day!

Since we talked about the summer solstice, let's take the summer solstice as an example.

For example, the summer solstice on 20 19 is at 23: 54 on June 2 1, then at 23: 54 on June 2 1, the sun is really directly on the tropic of cancer, not on June 2 1.

In other words, the time of the 24 solar terms should be understood as a "time point" (which is also said in the geography textbook of senior high school, with the same meaning, but not exactly the same expression), not a "day".

In fact, this is the truth from "It rains in beginning of spring" ... to slight cold and severe cold ",,"Not only the vernal equinox, summer solstice, autumn equinox and winter solstice, but also the time point of any solar term will change according to the changing law of the earth's orbit around the sun. It is said that the error of solar terms calculated by the Observatory has already reached the accuracy of one minute in 200 years.