Several Orthodox Christian churches go behind the Julian calendar for religious celebrations, then in many countries in Eastern European like Russia, Ukraine and Middle Eastern officially celebrated Christmas on January 7. The Julian calendar acts with 13 days backwards the Gregorian calendar which represented the criterion of international calendar in use in this days, and when the Orthodox Christian churches open the church calendar on January 7, they are in fact looking at 25 December. The Julian calendar made influence under the reign of Julius Caesar in 45BC. In 1582, Pope Gregory XIII made a new calendar to emend the contradiction between calendar time and calculated astronomical time. It became widely known as the Gregorian calendar. Nonetheless to start with only Catholic countries relied the changes and Orthodox Christian countries continued on the Julian calendar. With the time the exact countries relied the Gregorian calendar for nonreligious use but the Orthodox churches continued to standard their ceremonial calendar on the Julian schedule. (Julian calendar), suggested by Julius Caesar in 46 BC was a re-form of the Roman calendar. It entered into force on 1 January 45 BC in a little while before the Roman occupation of Egypt. It was the most important calendar in the Roman world, generality of Europe, until it was reiterated and slowly but surely changed by the Gregorian calendar. The Julian calendar earning versus the mean orbital year at the average of one day in 128 years. For the Gregorian the idea is one day in 3,030 years. The dissimilarity in the medium length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is around 0.002%.