37. In ancient Egypt the year was
divided into three seasons, each about four lunar months in length. The first
season was called akhet or “inundation,” approximately July to October,
and was the time when the Nile rose and overflowed the fields. The second was peret
or “coming forth,” approximately November to February, when the fields emerged
again from the flood waters and seeding, tilling, and growth of crops took
place. The third was schemu or “deficiency,” approximately March to June,
when harvest was followed by the time of low water before the next inundation.
The recognition of these seasons, based upon climatic and agricultural factors,
was undoubtedly very old.
38. At least by the start of the Old
Kingdom astronomical knowledge was well advanced, and astronomical factors
related to the calendar were soon recognized. At an early time the year probably
started with the lunar month which began after the Nile began to rise. The rise
of the river normally began at Aswan in late May or early June, and was about
ten days later at Memphis. Coming thus in the summer, the period of the great inundation
included the time of the summer solstice (§32). At about the same time a
celestial phenomenon took place which also attracted attention in Egypt at an
early date, namely the heliacal rising of Sirius. Sirius is the brightest of
all the fixed stars, and was known as Sothis in the Greek spelling of its
Egyptian name (Sopdu), and also as Canicula, the Dog Star. After being hidden
below the horizon for seventy days, Sirius reappeared in the east just before
the sunrise (heliacal rising), and this took place at about the beginning of
the annual inundation of the Nile. It may be added that the heliacal risings of
thirty-six stars or constellations (Orion, etc.), which occurred approximately
every ten days, were also noted and used, under the name of decans, to
mark as many periods of the year. Returning to Sirius, the length of the year
from heliacal rising to heliacal rising of Sirius was very close to the length
of the solar year (only twelve minutes shorter) which as we have seen (§33),
is now calculated as 365.24219879 days. In Table 4 the length of the Sirius-year
is shown at several intervals:
TABLE 5. The
Length of the Sirius-Year
|
Sirius-Year |
Length in Days |
|
4231 B.C. |
365.2498352 |
|
3231 |
365.2500000 |
|
2231 |
365.2502291 |
|
1231 |
365.2505225 |
|
231 |
365.2508804 |
|
A. D. 770 |
365.2513026 |
Thus, in 3231
B.C., the Sirius-year was 365 ¼ days in length, exactly the same as the value
taken for the Julian year (§144), and it became longer only very slowly.
In terms of the Julian calendar, the reappearance of Sirius at dawn in the
latitude of Memphis fell on July 19 from the fifth millennium to the second half
of the first millennium B.C.—i.e., throughout the whole course of ancient
Egyptian history—and then gradually moved to July 20. In the same period of
four thousand years, from 4231 to 231 B.C., in which the heliacal rising of
Sirius moved later by one day in comparison with the Julian year, the summer
solstice on the other hand, moved thirty-one days earlier in the Julian year,
namely from July 28 in the year 4231 to June 27 in the year 231 B.C. In
accordance with these changes, the summer solstice took place in Memphis in the
forty-third century (4300-4201) B.C., nine days after the heliacal rising of
Sirius; in the thirty-first century (3100-3001) B.C., on the same day, i.e., on
July 19; and in each century thereafter fell back another eighteen and
two-thirds hours. Thus, if the great summer inundation was originally taken as
signaling the beginning of a new year in an agriculturally oriented reckoning,
these two celestial events which fell within the same period, the summer
solstice and the heliacal rising of Sirius which was at one time exactly
coincident therewith, were available to provide a more precise point of
beginning in an astronomically oriented reckoning. Since the reappearance of
Sirius at sunrise was the more readily observable event, it is probable that
this was what was first utilized. In fact, an inscription of the First Dynasty
probably reads: “Sothis, the opener of the year; the inundation.” Since the
event of the heliacal rising had the remarkable stability which we have noted,
it provided a fixed point of reference for a very long time, as we shall see (§§41,
45-48). (Jack Finegan, Handbook
of Biblical Chronology [rev ed.; Peabody, Mass.: Hendrickson Publishers,
2008], 19-20)