Wherever the Common Era Calendar (a.k.a. the Gregorian Calendar)
is used — and it is now used by the governments of all
countries — a week of seven days is also used in conjunction
with it. But there is no 7-day cycle in Nature from which this
could have been derived, so why a week of seven days?
People use a 7-day week because they have been born into a world
where this is customary. In other words, the 7-day week has been
received from earlier generations. It has a long history. When
the Roman emperor Constantine made Christianity the state
religion early in the 4th Century CE the 7-day week was
officially associated with the Julian Calendar, and the
association remained after the Julian Calendar was replaced by
the Gregorian Calendar in the 16th Century CE.
The Christians received the 7-day week from the Jews. Their
explanation for its use is that this was commanded by their god,
named by them YHWH (using the Hebrew letters Yod-He-Vav-He). The
Jewish Pentateuch (incorporated into the Old Testament of the
Christian Bible) contains several injunctions attributed to YHWH
which mention “a seventh day”, upon which no “work” is to be
done.
So clearly a 7-day week was in use at the time of Moses in the
middle of the 2nd millennium BCE, but the 7-day week is much
older than that, since it was also used by the Sumerians and
Babylonians. Kerry Farmer remarks that “Some historians believe
that around 2350 BC Sargon I, King of Akkad, having conquered Ur
and the other cities of Sumeria, instituted a seven-day week,
the first to be recorded.”
In many European languages the names of the days of the week are
derived from the names of planets/gods. According to Dr Kelley
Ross the names for the planets/gods in Sumerian, Babylonian,
Greek, Latin and English, with the English name of the
corresponding day of the week in parentheses, are as follows:
Utu, Shamash, Helios, Sol, Sun (Sunday)
Nanna, Sin, Selene,
Luna, Moon (Monday)
Gugalanna, Nergal, Ares, Mars, Mars
(Tuesday)
Enki, Nabu, Hermes, Mercurius, Mercury
(Wednesday)
Enlil, Marduk, Zeus, Iuppiter, Jupiter
(Thursday)
Inanna, Ishtar, Aphrodite, Venus, Venus
(Friday)
Ninurta, Ninurta, Kronos, Saturnus, Saturn
(Saturday)
It is plausible to suppose that the association of planets and
days of the week arose in prehistoric times as follows:
At some point in the evolution of humans, perhaps as far back as
100,000 years ago, they acquired sufficient intelligence to
observe their environment and start to think about it. Obviously
the night sky would have been of interest to early humans. The
more intelligent among them would have observed that all of the
luminous objects in the night sky maintained their positions
relative to each other except for a few. Those that did not
appeared to wander across the night sky (relative to the fixed
stars), and thus eventually came to be called “wanderers”. (The
English word “planet” is derived from the Greek “planetes”,
which means exactly “wanderers”.)
We may assume that tens of thousands of years ago humans did not
think of the physical world as we do today, and in particular
did not have an idea of the Earth as a large spherical object
within a vast 3-dimensional space in which other large spherical
objects moved. For them the nature of the luminous objects which
they observed to wander along a band of the night sky, and the
cause of their movement, was unknown. But since (by observation
of the natural world) it was only living things which moved of
themselves, it would be reasonable for early humans to assume
that the wanderers, the planets, were living beings of some kind
– beings of a very unusual nature, what we might now call
“gods”.
So for early humans the planets were gods. And obviously the Sun
and the Moon belonged to their company. So how many gods were
there? As many as could be observed (perhaps more). In addition
to the Sun and the Moon there were five others (what we now call
Mercury, Venus, Mars, Jupiter and Saturn). If days somehow
became associated with these gods then we have the basis for a
period of seven days. Perhaps a particular god was venerated
each successive day without a break, which would give rise to
repeated periods of seven days.
It is plausible to suppose that the earliest calendars were
simple tallies of days from one new moon to the next (where “new
moon” means the reappearance of the moon after two or three days
of invisibility). Bones with 29 and 30 scratches have been found
which are at least 40,000 years old, suggesting (since a
lunation is approximately 29.5 days) that the scratches were a
record of days (or nights) in a lunation. This was probably the
first attempt by humans to divide the sequence of days into
periods. They would quickly have noted that four successive
7-day periods were almost, but not quite the number of days from
one new moon to the next. This might have given rise to a
calendar (such as is known to have been used by the Sumerians
and Babylonians) in which the days of a lunation (a “month”)
were divided into four 7-day periods beginning with a new moon,
followed by one or two days (not part of any 7-day period) until
the next new moon.
The origin of the 7-day week is sometimes attributed to dividing
the 29 or 30 days of a lunation by four, to get a number close
to seven. But a concept of division, which we find easily
understandable, is not a concept that we can attribute to the
earliest thinking humans. Counting and addition may have been
the most advanced mathematical concepts for many thousands of
years before the idea of division (as a numerical operation) was
discovered.
On the basis of this explanation of the development of the idea
of the week it is obvious why there are seven days in a week:
This is the number of visible planets plus the Sun and the Moon.
An immediate corollary is that there is nothing sacred (except
in the minds of some people) about the fact that a week has
seven days.
If, instead of an asteroid belt between Mars and Jupiter, there
had been a planet, then there would have been six visible
planets, not five, so the number of celestial entities would
have been eight, not seven. In that case humans would have
developed a week of eight days, not seven.
The Moon is thought by many astronomers to have been formed as a
result of a collision of the Earth with a planet-sized object
shortly after its formation over four billion years ago. If
(assuming that is what happened) that collision had never
occurred, and that no large body was subsequently captured by
the Earth, then the Earth would have no moon, in which case the
number of celestial entities would have been six, not seven. In
that case humans would have invented a week of six days, not
seven.
The planet Uranus was first observed by telescope in 1690 (by
Flamsteed) but was recognized as a planet (by Herschel) only in
1781. Neptune was first observed in 1846. Had the solar system
formed in such a way that these planets came close enough to
Earth to be observable with the naked eye then the number of
celestial entities would have been nine, and we would have a
9-day week. Actually the Maya had a 9-day week, with the days
assigned to nine gods, called the Lords of the Night. One might
speculate that the Maya knew (or were informed) that there were
two more “gods” which were invisible (Pluto perhaps not being
regarded as a fully accredited planet/god), though there is no
other evidence supporting this idea.
The fact that humans have long used a week of seven days is thus
the result of accident, namely, the fact that the solar system
is the way it is, with five of the nine planets being
sufficiently close to Earth to be visible with the naked eye.
The “sacredness” of the number seven is due to the association
of the seven celestial beings (the visible planets plus the Sun
and the Moon) with gods in the minds of early humans. This
“sacredness” is thus illusory. And thus so too is the
“sacredness” of the 7-day week. Accordingly there is no reason
to preserve it, except from an exagerated respect for tradition.
Those who adhere to some religion within which a 7-day week is
given prominence will, of course, wish to retain a 7-day week in
any new calendar. But for those whose minds are not constrained
by religious (or astrological) tradition there is no reason to
preserve a 7-day week. A week of 6 or 8 days may be considered
on its merits, or even a week with a variable number of days.
Such a week — of 6, 7, 8 or 9 days, in accord with the variable
length of quarter-lunations as they actually occur — is part of
a calendar invented in 2005 called “the Hermetic Lunar Week
Calendar”.
