Determination of the day of the week day of the week begins by starting from an ‘anchor date’: a known pair (such as January 1, 1800 as a Wednesday), determining the number of days between the known day and the day that you are trying to determine, and using arithmetic modulo 7 to find a new numerical day of the week. One standard approach is to look up (or calculate, using a known rule) the value of the first day of the week of a given century, look up (or calculate, using a method of congruence) an adjustment for the month, calculate the number of leap years
Names of the days of the week seven-day week spread throughout the Roman Empire in Late Antiquity. By the 4th century, it was in wide use throughout the Empire, and it had also reached India and China. The Greek and Latin names are as follows: Except for modern Portuguese and Mirandese, the Romance languages preserved the Latin names, except for the names of Sunday, which was replaced by "[dies] Dominicus (Dominica)", i.e. "the Lord's Day" and of Saturday, which was named for the Sabbath. In Corsican, the Saturday is known either by Sabatu or De Sadorn. Early Old Irish adopted the names from Latin, but introduced separate