Egyptian calendar
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The ancient civil Egyptian calendar, known as the Annus Vagus (vague year) or "Wandering Year", had a year that was 365 days long, consisting of 12 months of 30 days each, plus 5 extra days at the end of the year. The months were divided into 3 "weeks" of ten days each.

This calendar was in use by at least 2700 BCE, but probably before that. A text from the reign of First Dynasty King Djer indicates that the Egyptians had already established a link between the heliacal rising and the beginning of the year. The Egyptians seem to have used a lunar calendar at an earlier date, but when they discovered the discrepancy between the lunar calendar and the actual passage of time, they switched to a calendar based on the Nile inundation. The first inundation according to the calendar was observed in Egypt's first capital, Memphis, at the same time as the heliacal rising of Sirius (Egyptian Sopdet, Greek Sothis). The Egyptian year was divided into the three seasons of akh.t (Inundation), pr.t (Growth - Winter) and shomu (Harvest - Summer).

The heliacal rising of Sothis returns to the same point in 1461 days, not the 1460 days (of 4 calendar years of 365 days)so the difference between a Sothic sidereal (Julian) year and a civil year is 1 day in 4 years. Centuries later, this mistakenly appears to be the seasonal year. The civil calendar as a constant 365 days (without leap day), presumed the rising star to return to the same date in the calendar every 1461 calendar years equal 1460 years (called a Sothic cycle). It is not seasonal (Gregorian) because in 1460 years a Julian date is 12 leap days more than 1460 seasonal years. The dates of the Julian calendar (46 BC) reveal that Egypt was aware of the 1508-year seasonal cycle, but Egypt chose to favor the Sothic cycle. The Maya noted this 48-year (12 leap day) difference for the seasonal year; 1508 calendar years equal 1507 seasonal years (Gregorian).

Similarly, the Egyptians were aware that 309 lunations nearly equalled 9125 days, or 25 Egyptian years, which was used in the 12th dynasty. (Parker, Chicago Oriental Institute: 1991 BC)

For much of Egyptian history, the months were not given individual names but rather were numbered within the three seasons. As early as the Middle Kingdom, however, each month was given its own name. These finally evolved into the New Kingdom months, which in turn gave rise to the Hellenized names that were used among others for chronology by Ptolemy in his Almagest. Astronomers in the Middle Ages used it as well because of its mathematical regularity—Copernicus for example constructed his tables for the motion of the planets based on the Egyptian year. The convention amongst modern Egyptologists is to number the months consecutively using Roman numerals.

According to Roman writer Censorinus, the Egyptian New Year's Day fell on July 20 in the Julian Calendar in 139 CE, which was a heliacal rising of Sirius in Egypt. This is a calculation of Sothis that scholars feel is a correction from the record which logs July 21 of 140 AD. From this it has been miscalculated that previous risings of Sothis on the Thoht 1 New Year was 1322 BCE, and before that was 2782 BCE. The 1460-year cycle is a misnomer; the current cycle is 1460 years, but the previous cycle presumed by Egypt as 1460 years was only 1452 years drifting from July 18 to July 20. Astronomers, and Richard Parker (Chicago Oriental Institute) prove the arc of vision for 1872 BC is July 17, making the previous cycle 2770 BC, not 2782 BC. This latter date has been postulated as the time when the calendar was invented, but Djer's reign preceded that date. Other 19th century historians pushed it back another whole cycle, to 4242 BCE July 20 (12 years earlier than Sothic new year rise). A respect for previous accurate scholars is frequently lost, and a return to previous pseudo-science myth is common. The rise of Sothis varies in Egypt as one day per degree of geolatitude. Memphis is July 20 (Gregorian Aug 2); to the north Alexandria is July 21, to the south Thebes is July 15, and Quban on the tropic line is July 13. Precess the sky back to the period 2770-1872 BC and these risings occure 3 days earlier.

In 238 BCE, the Ptolemaic rulers decreed that every fourth year should be 366 days long rather than 365. The Egyptians, most of whom were farmers, did not accept the reform as it was the agricultural seasons that made up their year. The reform eventually went into effect with the introduction of the "Alexandrian calendar" by Augustus in 26/25 BCE, which included a sixth epag omenal day for the first time in 22 BCE.[1]

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 fellahin to calculate the agricultural seasons. Contemporary Egyptian farmers, like their ancient predecessors, divide the year into three seasons, namely winter, summer and inundation. It is also associated with local festivals such as the annual Flooding of the Nile and the ancient Spring festival sham en nisim.

The Ethiopian calendar is based on this 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.
Months No. Seasonal Names Middle Kingdom New Kingdom Greek Coptic Egyptian Arabic
I First of Akhet Tekh Dhwt Thoth Thout Tout
II Second of Akhet Menhet Pa-n-ip.t Phaophi Paopi Baba
III Third of Akhet Hwt-hwr Hwt-hwr Athyr Hathor Hatour
IV Fourth of Akhet Ka-hr-ka Ka-hr-ka Choiak Koiak Kiahk
V First of Proyet Sf-bdt Ta-'b Tybi Tobi Touba
VI Second of Proyet Rekh wer Mḫyr Mechir Meshir Amshir
VII Third of Proyet Rekh neds Pa-n-amn-htp.w Phamenoth Paremhat Baramhat
VIII Fourth of Proyet Renwet Pa-n-rnn.t Pharmouthi Paremoude Baramouda
IX First of Shomu Hnsw Pa-n-ḫns.w Pachon Pashons Bashans
X Second of Shomu Hnt-htj Pa-n-in.t Payni Paoni Ba'ouna
XI Third of Shomu Ipt-hmt Ipip Epiphi Epip Abib
XII Fourth of Shomu Wep-renpet Msw-r' Mesore Mesori Mesra

[edit] Notes