Why are there seven days of the week, and why is this period of time such a fundamental subdivision of the year? What’s natural about it? In the month, for example, we have the natural cycle of the moon. What is seven days long? As cycles and rhythms go, using seven as the basis does not lend itself to computations, especially those that involve division by other numbers. In this regard, the only integer in the Base 10 system that does not divide evenly into 360 (degrees or days) is 7.
There are, in fact, references to the idea that the most sacred numbers are 7 and 12 -- neither of which could be construed as convenient numbers in a Base 10 system. Despite the difference between the two, 5, being considered a sign of life, and part of the sacred-ness of Sacred Geometry, 7 and 12 are curious numbers. They are, of course, well used in terms of the number of chakras, days, wonders of the world -- and months, disciples, jurors, and so forth. But where’s the natural connection?
The Bible’s Book of Genesis tells of the creation of the world in six days, after which God rested on the seventh. As such the seventh day became the Jewish day of rest, the Sabbath (what is now known as Saturday). But other civilizations from Babylon to Persia to Rome before the advent of Christianity also used the 7-day week. [One might suggest that the Jews got the idea during the years of captivity in Babylon, circa 600 B.C.E.] Later, when Pope Gregory did his calendar shift thing in 1582 -- wiping out ten days of October in the process -- he did not touch the seven days of the week, and Thursday, October 21st, followed Wednesday, October 10th, without so much as a genuflection.
One suggested possibility for the magic of seven is a very practical consideration. If one wraps, for example, a rope or string around 7 cylinders, a perfect hexagon is formed with the seventh cylinder in the middle. This is the only stable configuration of wrapping more than three cylindrical objects. Four, five, and six objects will slip from one configuration to another. Ancients in the process of wrapping tent poles, small logs for firewood, Sumerian cylindrical seals, or other such objects might have come upon this number and attached a mystical significance to it. This is supposedly, the sort of thing upon which Sacred Geometry is ultimately based -- along with such realizations that “the ratios between the fundamental forces seem specifically tuned to produce an amazingly complex, beautiful, and enduring universe.” 
Maybe, but the derivation of the sacredness of Seven is much more likely to be derived from astronomical observations. There are, in fact, seven “wanderers” in the sky -- the sun, moon, and five visible planets (other than Earth). The ancients were exceptionally keen on astronomy for a host of reasons -- including the fact they could see the night sky in all of its glory (unlike most of modern city folk), and the likelihood that collisions with extraterrestrial objects (e.g. Venus, Mars, Comet Shoemaker-Levy) occurred just often enough to really gain anyone’s attention. The astronomical connection is likely the most obvious and shows up in the attachment of planets to each day of the week.
For example, the visible planets still retain their place in the English names -- with Satur(n)-day, Sun-day, and Mo(o)n-day being the most obvious. The other four, meanwhile, derive from the names of Anglo-Saxon or Nordic gods (who replaced the names of Roman gods). Thus, Tuesday is “Tiw”s day”, Wednesday, “Woden’s day”, Thursday is “Thor’s day”, and Friday is “Freya’s day”. Other languages, including Hindi, Japanese and Korean, also have a similar naming relationship.
The end result is:
Sunday is ruled by the Sun, and dedicated to getting in touch with one’s most basic and fundamental self. It is potentially a very personal day.
Monday is ruled by the Moon, and constitutes a very emotional, nurturing time (and disastrous in terms of a day to start the work week).
Tuesday is ruled by Mars, and great for initiating things, such as beginning the workweek, and most any other endeavor.
Wednesday is ruled by Mercury, and is ideal for continuing the workweek, and in
Thursday is ruled by Jupiter and great for planning and finishing up the workweek.
Friday is ruled by Venus, and great for making love, having fun and partying. Duh!
Saturday is ruled by Saturn, and constitutes the best time to fulfill one’s obligations to society (i.e. the true Sabbath).
[The above also implies the desirability of a three-day work week, say 9 hours per day!]
As to the order in which one day follows another day of the week, this too is fairly simple. It begins by placing the seven planets in an evenly spaced circle in an order of their “period of revolution” about the earth. In this case, the sequence from longest to shortest orbital periods is: Saturn, Jupiter, Mars, Sun, Venus, Mercury, and the Moon. One then connects each one using a seven pointed star, starting first with the Sun and going to the Moon. The next (across the circle) spot is then Mars (Tuesday). This continues such that Mars is followed by Mercury, Jupiter, Venus, and Saturn (and then back to the Sun-day).
This 7 pointed star -- planetary arrangement was also used by the ancients to denote the metals which were associated with each planet. Amazingly the result was an ancient system which replicated the modern day atomic number of these metals: Iron 26, copper 29, silver 49, tin 50, gold 79, mercury 80, and lead 82. The electrical conductivity sequence also appears around the outside of the circle, starting with lead! 
The Seven Day Week is amazingly fundamental. There is in fact no record of its cycle ever being broken. Calendar changes come and go, but the days of the week run in an apparently uninterrupted stream from at least the time of Moses (circa 1460 B.C.E.) until the present day (and likely go even further back in time). (There has been suggestions that the ancient Jews might have had a calendar which included an extra Sabbath, but this is probably not true.)
Finally, for the Jews, the Sabbath (Saturday) is the day of rest and worship. On this day God rested after creating the world. Most Christians have made Sunday their day of rest and worship, because Jesus rose from the dead on a Sunday. Muslims use Friday as their day of rest and worship. The Qur’an calls Friday a holy day, the “king of days.”
 John Martineau, A Little Book of Coincidence, Wooden Books, Walker & Company, New York, 2001.
2003© Copyright Dan Sewell Ward, All Rights Reserved [Feedback]