Қысқа нұсқада ежегіттер күнтізбесі

Calendar used in ancient Egypt before 22 BC

The ancient Egyptian calendar – a civil 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 five 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 decades. It has been suggested that during the Nineteenth Dynasty and the Twentieth Dynasty the last two days of each decan were usually treated as a kind of weekend for the royal craftsmen, with royal artisans free from work. Because this calendrical year was nearly a quarter of a day shorter than the solar year, the Egyptian calendar lost about one day every four years relative to the Gregorian calendar. It is therefore sometimes referred to as the wandering year (annus vagus), as its months rotated about one day through the solar year every four years. Ptolemy III's Canopus Decree attempted to correct this through the introduction of a sixth epagomenal day every four years but the proposal was resisted by the Egyptian priests and people and abandoned until the establishment of the Alexandrian or Coptic calendar by Augustus. The introduction of a leap day to the Egyptian calendar made it equivalent to the reformed Julian calendar, although by extension it continues to diverge from the Gregorian calendar at the turn of most centuries. This civil calendar ran concurrently with an Egyptian lunar calendar which was used for some religious rituals and festivals. Some Egyptologists have described it as lunisolar, with an intercalary month supposedly added every two or three years to maintain its consistency with the solar year, but no evidence of such intercalation before the 4th century BC has yet been discovered.

Following Alexander the Great's conquest of the Persian Empire, the Macedonian Ptolemaic Dynasty came to power in Egypt, continuing to use its native calendars with Hellenized names. In 238 BC, Ptolemy III's Canopus Decree ordered that every 4th year should incorporate a sixth day in its intercalary month, honoring him and his wife as gods equivalent to the children of Nut. The reform was resisted by the Egyptian priests and people and was abandoned.

Egyptian scholars were involved with the establishment of Julius Caesar's reform of the Roman calendar, although the Roman priests initially misapplied its formula and—by counting inclusively—added leap days every three years instead of every four. The mistake was corrected by Augustus through omitting leap years for a number of cycles until AD4. As the personal ruler of Egypt, he also imposed a reform of its calendar in 26 or 25BC, possibly to correspond with the beginning of a new Callipic cycle, with the first leap day occurring on 6 Epag. in the year 22BC. This "Alexandrian calendar" corresponds almost exactly to the Julian, causing 1Thoth to remain at 29August except during the year before a Julian leap year, when it occurs on 30August instead. The calendars then resume their correspondence after 4Phamenoth/ 29February of the next year.

The Calendars of Lucky and Unlucky Days seem to be based on scientific observation as well as myths. Periodicity has been established between phases of the moon as well as the brightening and dimming of the three star system Algol as visible from earth.

The calendars could also be used to predict someone's future depending on the day they were born. This could also be used to predict when or how they would die. For example, people born on the tenth day of the fourth month of Akhet were predicted to die of old age.

The epagomenal days were added to the original 360 day calendar in order to synchronise the calendar with the approximate length of the solar year. Mythologically, these days allowed for the births of five children of Geb and Nut to occur and were considered to be particularly dangerous. In particular, the day Seth was supposed to be born was considered particularly evil.

The reformed Egyptian calendar continues to be used in Egypt as the Coptic calendar of the Egyptian Church and by the Egyptian populace at large, particularly the fellah, to calculate the agricultural seasons. It differs only in its era, which is dated from the ascension of the Roman emperor Diocletian. Contemporary Egyptian farmers, like their ancient predecessors, divide the year into three seasons: winter, summer, and inundation. The Ethiopian calendar is based on this reformed calendar but uses Amharic names for its months and uses a different era. The French Republican Calendar was similar, but began its year at the autumnal equinox. British orrery maker John Gleave represented the Egyptian calendar in a reconstruction of the Antikythera mechanism.