A record of the days, weeks, and months of a current year. The calendar now used is that of pope Gregory XIII, whose decree established it in 1582. Before then the length of the year was simply the time it took for the earth to travel around the sun. Known as the Julian calendar, it was inaccurate because the earth's journey took a little less than three hundred sixty-five and a quarter days. This error amounted to ten days by Pope Gregory's time. In order to correct this it was calculated that the extra day of leap year would not occur in the century year unless it would be divisible by four hundred, hence 1600 and 2000 would be a leap year, 1700, 1800, 1900 would not be. The Pope suppressed ten days in 1582 and made the calendar obligatory on the Catholic faithful. Following the Gregorian calendar, there is an error of one day in thirty-five centuries. Two astronomers, Lilius and Clavius, had made the necessary calculations. At first Protestant countries refused to use it. England did not adopt the Gregorian calendar until 1752. Eastern Churches are gradually adopting it.