Intercalation (timekeeping) year of 365 days, an extra day ("leap day" or "intercalary day") about every four years, causing a leap year to have 366 days (Julian, Gregorian and Indian national calendars). The Decree of Canopus, which was issued by the pharaoh Ptolemy III Euergetes of Ancient Egypt in 239 BCE, decreed a solar leap day system; an Egyptian leap year was not adopted until 25 BC, when the Roman Emperor Augustus successfully instituted a reformed Alexandrian calendar. In the Julian calendar, as well as in the Gregorian calendar, which improved upon it, intercalation is done by adding an extra day to
Days of week on Hebrew calendar has 29 days and Kislev has 30 days). The months of Tevet and Shevat, months ten and eleven, have 29 and 30 days respectively. Finally, in a regular year the month of Adar has 29 days, while in a leap year Adar I of 30 days is added before the regular Adar, which becomes Adar II of 29 days. The result is that the period from 1 Tevet to 29 Cheshvan is fixed, except that in a leap year Adar I of 30 days is added; and all adjustments are made using 29/30 Cheshvan and/or 29/30 Kislev. The period from