1. Why are leap years ( intercalary years ) called leap years? 2. Xanthicus shall have 32 days in this intercalary year ." 3. The calendar seems to have employed several schedules to determine which of the 19 years will be intercalary years . 4. There is another theory which says that in intercalary years February had 23 or 24 days and Intercalaris had 27. 5. Mart . " were dates in late February in regular years, but were a month later in intercalary years . 6. However, the sources rarely reveal which years were regular, which were intercalary, and how long an intercalary year was. 7. The remainder, if tallies with the set sequence number of the prevailing Metonic cycle, then it will be an intercalary year . 8. The Qu'ran makes it clear that in intercalary years the number of months was expanded from its usual twelve ( see next section ). 9. Mart . ", normally referring to the end of February, were in intercalary years the concluding days of the " mensis intercalaris ". 10. The intercalary years are numbers 3, 6, 8, 11, 14, 17 and 19 . Both the Hebrew calendar and the Julian calendar use this sequence.