The curious case of the Milankovitch calendar

Abstract. The Gregorian calendar, despite being more precise than the Julian (which now lags 13 d behind Earth), will also lag a day behind nature in this millennium. In 1923, Milutin Milankovitch presented a calendar of outstanding scientific importance and unprecedented astronomical accuracy, which was accepted at the Ecumenical Congress of Eastern Orthodox churches. However, its adoption is still partial in churches and nonexistent in civil states, despite nearly a century without a better proposition of calendar reform in terms of both precision and ease of transition, which are important for acceptance. This article reviews the development of calendars throughout history and presents the case of Milankovitch's, explaining its aims and methodology and why it is sometimes mistakenly identified with the Gregorian because of their long consonance. Religious aspects are briefly covered, explaining the potential of this calendar to unite secular and religious purposes through improving accuracy in both contexts.