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I know that the Egyptians had a solar calendar, based on a certain effect of the sun over the Nile.

I also know that it held 365 days without any fix to the quarter a day a year (like Feb 29th every 4 years today).

How old and how common was the calendar?

How come the Egyptians didn't figure out that quarter of a day is missing?

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    How would you figure out that the quarter day was missing? Doesn't that require some pretty precise measurements of year length? Where does a 0.07% error have any impact in daily life? What research have you done so that we don't wind up telling you things you've already consulted? – Mark C. Wallace Sep 24 '18 at 10:41
  • I'm a history buff, I have high interest but no tools or knowledge to check these specifics, nor do I expect someone to actually "do some homework" for me, but if someone knows, I'de be happy to learn. and regarding the offset, if you're based on astronomy to count 365 days, 4 years later you would notice the offset... – Guy L Sep 24 '18 at 11:58
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    Welcome to the site. You got lucky and got a detailled answer quickly, but help center suggests that you document at least Wikipedia - and questions that include prior research tend to get better answers. Second, I'm still not sure how you would notice the 0.07% slippage? In any case, a worthwhile and interesting question and I'm glad you asked. – Mark C. Wallace Sep 24 '18 at 12:04
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    @GuyL might be interesting to note that today leap years are not every 4 years. They are every 4 years with specific exceptions (like if the year is divisible by some numbers (one is 400, can't remember the others)). In those exceptions, they SKIP the leap year. – user32121 Sep 24 '18 at 19:10
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    If we go into that discussion, then the Hebrew lunar calendar has a much more complex system, to keep the lunar system aligned with seasons of the year, i.e with the solar system... :) – Guy L Sep 24 '18 at 19:12
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The earliest certain attestation of the solar calendar in Egypt dates to the reign of the Fifth-dynasty Pharaoh Neferirkare, in the mid 25th century BCE. There are also possible earlier examples, but the best we can say is that the calendar was certainly in use early in Old Kingdom Egypt, and perhaps much earlier.

Current consensus credits its adoption to somewhere in the Second Dynasty, in the 28th or 29th century BCE. However, this understanding may change based on evidence from future excavations.

If you are interested in more detail, you might like to consult Marshall Clagett's 1995 book, Ancient Egyptian Science: Calendars, clocks, and astronomy (link below).


The Ancient Egyptian priests and officials would certainly have been aware of the 'missing' quarter day.

It is believed that the calendar was originally based based on the appearance of the star Sirius in the Egyptian night sky (Sirius is one of the brightest stars in the winter sky in the northern hemisphere). We have a large number of surviving records of the Ancient Egyptians recording the date of the first rise of Sirius on their calendar.

Thus, they would have realised fairly quickly that the 365 day calendar was inaccurate (after 4 years, Sirius would have appeared a day late!).

However, it is not clear that this would have mattered. The calendar seems to have been important for civil and religious purposes, but probably far less important for Egypt as a whole.

As an aside, the 365 days solar year was divided into 12 months of exactly 30 days, together with an additional 'intercalary month' of 5 days on which were celebrated the 'birthdays' or 'feast days' of the five main gods of the Memphite Cosmology: Osiris, Isis, Horus, Set, and Nephthys.

Dates were generally recorded as the Pharaoh's regnal year, followed by the month of the civil calendar, followed by the day of the month.


Although the civil calendar was a solar one, the lives of most Egyptians would have been governed by the three 'seasons', dictated by the cycles of the Nile:

  • Akhet (Ꜣḫt), or 'Flood' akhet
  • Peret (Prt), or 'Emergence' Prt
  • Shemu (Šmw), or 'Low Water' / 'Harvest' smw

(hieroglyph images from Wikipedia)

The exact dates of these 'seasons' varied year-by-year, dictated by the vagaries of the Nile flood. Dating the rise of the Nile to a solar calendar would probably have been of little importance to the vast majority of people in Ancient Egypt.


The various Egyptian calendars are discussed at length in Ancient Egyptian Science: Calendars, clocks, and astronomy by the historian Marshall Clagett.

  • Haven't gone looking for it, but one would imagine it would be blaringly obvious when the extra day was needed, and it was likely just added as a bonus holiday (lagniappe as we say in New Orleans) as needed by priestly decree. – T.E.D. Sep 24 '18 at 11:43
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    @T.E.D. Actually, it seems not (at least until the Greco-Roman period). They just seem to have accepted it. They had at least 2 other lunar calendars running at the same time, so did it really matter when the new year started? Given the mainly religious important of the solar calendar, I'd guess it had to do with the eternal nature of the gods. After all, if you're going to call your tomb a 'House of millions of years', the fact that it's going to take a millennium-and-a-half for the calendar to get back in sync is probably just a minor inconvenience! ;) – sempaiscuba Sep 24 '18 at 11:56
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    Them letting the calendar wander does help us today, because when they noted that Sirius rose on the first day of the year again, that was the completion of a Sothic cycle. By knowing various times when cycle was complete gives us a better timeline to place dates. – pboss3010 Sep 24 '18 at 14:16

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