Maundy Thursday April 22 inclusive, but these dates fall on different days depending on whether the Gregorian calendar or Julian calendar is used liturgically. Eastern churches generally use the Julian calendar and celebrate this feast throughout the 21st century between April 1 and May 5 in the more commonly used Gregorian calendar. The liturgy held on the evening of Maundy Thursday initiates the Easter Triduum, the period which commemorates the passion, death, and resurrection of Jesus; this period includes Good Friday and Holy Saturday, and ends on the evening of Easter. The Mass of the Lord's Supper or service of worship is
Armelin's calendar mind of modest ability will learn in a few minutes the weekday with which each month invariably begins, and will be able to compute quickly the day of the week upon which any day of any month falls. Each stated holiday falls upon its invariable day of the week. Thanksgiving Day falls always on November 30. A major disadvantage is for sabbatarians, who are obliged to worship every seventh day. Their holy day will occur on a different weekday every year. Armelin's project received the first premium of the French Astronomical Society. The World Calendar, roughly identical, has been promoted