Who invented the solid gas method?

He is Liu Zhuo, an astronomer in the Sui Dynasty.

"Twenty-four solar terms" is the only basis for dividing the earth branch of the moon column, so it is very important to determine the specific date of the twenty-four solar terms. However, the division method of the 24 solar terms has changed several times in history, which leads to the problem that the same historical figure will have different characters if he uses calendars of different periods to calculate. However, the change of the calculation method of the twenty-four solar terms has a great relationship with the "flat gas method" and "fixed gas method"

I know six things about calendars and astronomy, so I can only write what I understand. The biggest difference between the "leveling method" and the "fixing method" is that one is to divide the year into 24 equal parts to determine the solar terms, and the other is to divide the running angle of the sun into 24 equal parts to determine the solar terms. The former is the "flat gas method" and the latter is the "fixed gas method".

Because the earth's orbit (in fact, the ecliptic) is elliptical, the sun is sometimes far away from the earth and sometimes very close. Although the angles are the same, the radian of the sun is different, so the corresponding days are different.

Therefore, the time interval of the 24 solar terms calculated by the constant gas method is different, which leads to the formula of "June 21st in the first half of the year and August 23rd in the second half". The "6th, 2nd1day" and "8th, 23rd" here are actually the differences between the 24 solar terms determined by the "Fixed Air Method".