Leap year vernal equinox moves a day earlier in the calendar about every 131 years. The Revised Julian calendar adds an extra day to February in years that are multiples of four, except for years that are multiples of 100 that do not leave a remainder of 200 or 600 when divided by 900. This rule agrees with the rule for the Gregorian calendar until 2799. The first year that dates in the Revised Julian calendar will not agree with those in the Gregorian calendar will be 2800, because it will be a leap year in the Gregorian calendar but not in
Egyptian calendar equinox. British orrery maker John Gleave represented the Egyptian calendar in a reconstruction of the Antikythera mechanism. Egyptian calendar The ancient Egyptian calendar was a solar calendar with a 365-day year. The year consisted of three seasons of 120 days each, plus an intercalary month of 5 epagomenal days treated as outside of the year proper. Each season was divided into four months of 30 days. These twelve months were initially numbered within each season but came to also be known by the names of their principal festivals. Each month was divided into three 10-day periods known as decans or