TT #10 · Parashas Va’eschanan · First Aliyah · Passuk 4:6
You shall keep and do them, for that is your wisdom and your understanding in the eyes of the peoples, who will hear all these statutes and say, “Surely this great nation is a wise and understanding people.”
Torah Temimah points to Shabbos 75a (R’ Shmuel bar Nachmani in the name of R’ Yonasan: the mitzvah of calculating tekufos and mazalos).
English: R’ Shmuel bar Nachmani said in the name of R’ Yonasan: From where do we know that it is a mitzvah to calculate the seasons and the constellations? As it is said, “for that is your wisdom and your understanding in the eyes of the peoples” — which wisdom and understanding is in the eyes of the peoples? Say: this is the calculation of the tekufos and mazalos.
Custom (identification of the public chokhmah with the science of the calendar and stars).
Calculating the seasons and the heavenly bodies is a mitzvah whose wisdom is visible to the nations and thereby glorifies Israel.