What’s the difference between the Julian and Gregorian calendars?
A. The difference between the two calendars lies precisely in how they resolve this problem. The Julian calendar’s solution was to add a leap day every four years, with the end result that the Julian calendar year was an average of 11 minutes and 14 seconds longer than the earth’s actual journey around the sun. This meant that the astronomical facts and the calendar calculations would eventually be out by one day in every 128 years. The real equinox, for instance, would then happen one day earlier than the date given on the calendar. The Gregorian calendar attempted to correct this by shortening the average calendar year. It introduced the additional rule that, in contrast to the Julian calendar’s leap-year rule, there would be no leap day in years whose number could be divided directly by 100 but not by 400. Thanks to this reduced number of leap years, the Gregorian calendar comes closer to astronomical reality – although it, too, is not “exact” – but the difference between the facts
