Determination of the day of the week possible to do all the calculations in one's head with a little practice). None of the methods given here perform range checks, so unreasonable dates will produce erroneous results. Every seventh day in a month has the same name as the previous: "Corresponding months" are those months within the calendar year that start on the same day of the week. For example, September and December correspond, because September 1 falls on the same day as December 1. Months can only correspond if the number of days between their first days is divisible by 7, or in other words, if their
Easter Monday Liturgy; while this is prescribed for all days of that week, often they are only celebrated on Monday and maybe a couple of other days in parish churches, especially in non-Orthodox countries. Also, when the calendar date of the feast day of a major saint, "e.g.", St. George or the patron saint of a church or one's name day, falls during Holy Week or on Easter Sunday, the saint's day is celebrated on Easter Monday. Easter Monday is an official holiday in the following countries. Nations on this list indicated as "Eastern Christian" observe Easter according to the Julian Calendar