A peculiar liturgical puzzle has persisted for centuries in Jewish diaspora communities: why do Jews outside Israel begin praying for rain on December 4th or 5th, while those in Israel start on the seventh of Marheshvan? The answer lies in an ancient astronomical miscalculation that continues to ripple through time. Through historical, talmudic, and astronomical analysis, this research traces how Samuel's third-century calculation of sixty days from the autumnal equinox—based on a 365.25-day year rather than the actual 365.2422 days—combined with the 1582 Gregorian calendar reforms to create an increasingly misaligned prayer schedule. The investigation reveals that diaspora communities unknowingly follow ancient Babylonian agricultural timing rather than local climate patterns, transforming a practical weather petition into a largely symbolic ritual. As this calendrical drift continues, the prayer dates advance approximately three days every 400 years, creating a minor but persistent anomaly in Jewish liturgical practice that will continue until either messianic intervention or rabbinical calendar reform addresses the discrepancy.