The intercalary month or epagomenal days of the ancient Egyptian, Coptic, and Ethiopian calendars are a period of five days in common years and six days in leap years in addition to those calendars' 12 standard months, sometimes reckoned as their thirteenth month. They originated as a periodic measure to ensure that the heliacal rising of Sirius would occur in the 12th month of the Egyptian lunar calendar but became a regular feature of the civil calendar and its descendants. Coptic and Ethiopian leap days occur in the year preceding Julian and Gregorian leap years. Names The English names "intercalary month" and "epagomenal days" derive from Latin ("proclaimed between") and Greek epagómenoi () or epagómenai (, "brought in" or "added on"), Latinized as . The period is also sometimes known as the "monthless days". In ancient Egypt, the period was known as the "Five Days upon the Year" (), the "Five Days" () or "Those upon the Year" (), the last of which is transliterated as . Parker also proposed that in some cases the intercalary month was known by the name Thoth () after the festival that gave its name to the following month. In modern Egypt, the period is known as or (, Pikouji n'Abot, ."The Little Month") and Al-Nasi (, en-Nasiʾ, ."The Postponement"), after Nasi' of the Pre-Islamic calendar. The Arabic name is also romanized as Nasie. In Ethiopia, the period is known as Paguemain, Phagumien (, Ṗagʷəmen), Pagume, or Pagumay (, Ṗagume). Egyptian calendars Ancient Until the the beginnings of the months of the lunar calendar were based on observation, beginning at dawn on the morning when a waning crescent moon could no longer be seen. The intercalary month was added every two or three years as needed to maintain the heliacal rising of Sirius within the fourth month of the season of Low Water. This month may have had as many as 30 days. According to the civil calendar, the months fell in order with the rest regardless of the state of the moon. They always consisted of 30 days, each individually named and devoted to a particular patron deity, but the year was always followed by an intercalary month of only five days. Owing to the lack of a leap day, the calendar slowly cycled relative to the solar year and Gregorian date until the Ptolemaic and Roman eras. The period of the intercalary