A calendar, named for Gaius Julius Caesar and introduced in Rome in 46 B.C., that established the twelve-month year of 365 days. It was adopted throughout much of the Western world, including Kievan Rus and Muscovy . The Julian calendar s year, however, was over eleven minutes too long compared with the solar year, i.e., the time the earth requires to make one revolution around the sun. Because of this discrepancy, Pope Gregory XIII introduced a revised calendar in 1582 that had a shortened year and then omitted the ten excess days that had accumulated since A.D. 325, the year of the Council of Nicea, which was chosen as the base year. Although most of the Western world adopted the Gregorian calendar, Russian regimes retained the Julian calendar termed old style or O.S. until after the Bolshevik Revolution . On February 1, 1918 O.S., the Bolsheviks introduced the Gregorian calendar and omitted the thirteen excess days that had accumulated since A.D. 325, thus making that day February 14, 1918 new style or N.S. . The Russian Orthodox Church and other Eastern Christian churches continue to use the Julian calendar.
