Feast of the Ascension term "Holy Thursday" to mean Ascension Day is rare, and the term is more generally applied by most Christian denominations to Maundy Thursday in Holy Week. In Western Christianity, the earliest possible date is April 30 (as in 1818 and 2285), the latest possible date is June 3 (as in 1943 and 2038). In Roman Catholicism, the Ascension of the Lord is a Holy Day of Obligation and in the Anglican Communion, Holy Thursday is a Principal Feast. The three days before Ascension Thursday are sometimes referred to as the Rogation days, and the previous Sunday — the Sixth Sunday
Adoption of the Gregorian calendar 12 days, only 11 were skipped, and the day of the week was repeated on successive days, because at the same time the International Date Line was moved, from following Alaska's eastern border with Canada to following its new western border, now with Russia. Many of the countries of eastern Europe were Eastern Orthodox or Islamic and adopted the Gregorian calendar much later than western Christian countries. Roman Catholic countries such as the Polish–Lithuanian Commonwealth adopted the "new style" (N.S.) Gregorian calendar in 1582 (switched back in 1795 after Third Partition of Poland), but the switch to the Gregorian calendar