Tahisas 12 is different from December 21.

Professor Ephraim Isaac is my hero because he asserted that "Ethiopian calendar belongs to neither Julian nor Gregorian (1999 Ec)". Following him and given one day is one rotation of earth, I inquired Ethiopian calendar belongs to whom? Empirically, I have compared and analyzed 68 years data of the Ethiopian calendar and Gregorian calendar (1932-1999 EC). My finding was that Ethiopian calendar belongs to the tropics, when the Gregorian does to the temperates.