[The] collection of seven gods, seven days, and seven worlds - the Sun, the Moon, and the five wandering planets - entered the perceptions of people everywhere. The number seven began to acquire supernatural connotations. There were seven "heavens", the seven transparent spherical shells, centred on the Earth, that were imagined to make the worlds move. The outermost - the seventh heaven - is where the "fixed" stars were imagined to reside. There are Seven Days of Creation (if we include God's day of rest), seven orifices to the head, seven virtues, seven deadly sins, seven evil demons in Sumerian myth, seven vowels in the Greek alphabet (each affiliated with a planetary god), Seven Governors of Destiny according to the Hermetists, Seven Great Books of Manichaeism, Seven Sacraments, Seven Sages of Ancient Greece, and seven alchemical "bodies" (gold, silver, mercury, lead, tin, and copper - gold still associated with the Sun, silver with the Moon, iron with Mars, etc.). The seventh son of a seventh son is endowed with supernatural powers. Seven is a "lucky" number. In the New Testament's Book of Revelations, seven seals on a scroll are opened, seven trumpets are sounded, seven bowls are filled. St Augustine obscurely argued that for the mystic importance of seven on the grounds that three "is the first whole number that is odd" (what about one?), "four is the first that is even" (what about two?), and "of these . . . seven is composed. And so on. Even in our time these associations linger.And that was before Harry Potter and the seven Horcruxes, not to mention seven Weasley siblings, and George R R Martin's "A Song of Ice and Fire" series in which a major religion is centred on seven gods and whose holy book is called "The Seven-Pointed Star". Not to mention seven colours in a rainbow. If you can take a really good photograph of one, and distinguish blue from violet in colour, and the two of them each take up as much room as any of the other colours, I'd love to see it - I honestly have yet to see a rainbow like that (much as I like blue and indigo).
The existence even of the four satellites of Jupiter that Galileo discovered - hardly planets - was disbelieved on the grounds that it challenged the precedence of the number seven. As acceptance of the Copernican system grew, the Earth was added to the list of planets, and the Sun and Moon were removed. Thus, there seemed to be only six planets (Mercury, Venus, Earth, Mars, Jupiter, and Saturn). So learned academic arguments were invented showing why there had to be six. For example, six is the first "perfect" number, equal to the sum of its divisors (1 + 2 + 3). Q.E.D. And anyway, there were only six days of creation, not seven. People found ways to accommodate from seven planets to six . . .- Carl Sagan, "Pale Blue Dot", 1994
Anyway, doing some totally unrelated research, I stumbled upon the Babylonians. I knew they were responsible for 360º , 60 seconds a minute and 60 minutes an hour, and probably for popularising algebra (I recommend Marcus de Sautoy's "The Story of Maths"!), and I knew they were very meticulous astronomers, but I hadn't previously come across the intricacy of their days of the week system.
It was in a book I was reading, and not one recently published, so being an incorrigible skeptic I had to go online to get an independent corroboration. (No, that's honestly nothing to do with the trolls on the Guardian comments pages accusing me of "getting all my information from the Guardian" when in fact I was getting most of it from the Sense About Science website! Although one does wonder what they were doing there if they so despise it . . .) It was quite a trawl. I found plenty of sources confirming that each of the ancient "planets" (in those days, "wandering stars" - stars that did not move across the sky at the same speed as other stars) had its own weekday, such as here, here and here. And I ended up reading part of an interesting book about the origins of weekdays. Following the French Revolution, a ten day week was imposed - but it just didn't work.
Ancient Inventions even claims that "when the Babylonians invented the seven-day week, they anticipated the findings of 20th century biologists. It has recently been discovered that the human body is governed by a seven-day biorhythm, which is detectable from small variations in blood pressue and heartbeat as well as response to infection and even organ transplants. The same biorhythm affects other life-forms, even simple organisms such as bacteria."
I'm not entirely sure I buy this. The only source it cites is a book (which may or may not be correct but I am not going to go and ask my library for before I post this!), but furthermore their wording makes no differentiation between cause and effect. The shells of some coastal critters or other that grew near towns during the Industrial Revolution show layers of growth like tree rings - and every seventh layer is palest, i.e. the ones they grew on Sunday when the factory was shut. (Source: memory of a lecture in my degree. Take with pinch of salt to suit your taste, but I have a nerdy memory for random facts.) Besides, human timekeeping is not to 24 hours - it's longer. This is not even a relic of a past when the Earth was spinning faster, or it would be shorter. And in any case, seven is not a universal special number - in China, for instance, the "lucky number" is eight.
Still, it could be true. I'm guessing the bacteria in question are influenced by the same things humans are influenced by - pollution, for instance, probably occurs at different timescales and intensities at weekends. But you never know.
So, in attempting to research one thing, I came across the Babylonians and their planetary systems and timekeeping, and in attempting to research that, I came across a lot of other things, and I hastily stopped there. Research is great fun, though! And by the way, it isn't something I have a clue how to do academically. So don't feel unqualified to go looking things up.
Sorry, but after all that, the best pages I have to show you are Wikipedia: Planetary Hours and Week-Day Names. The latter at least has obviously had a lot of source verification put into it. (Wiki can actually be very strict - Rick Nowell on the Galaxy Zoo Forum found that creating the "Peas" page was a huge task due to the very tight sourcing rules. My research of the entire project - which was used, for example, in selecting names to go in the acknowledgements on the papers - was disallowed because it was a blog post.)
Anyway, to summarise on the ancient deities to whom the planets were assigned. Sunday of course was the Sun, Monday the Moon - those are obvious. Tuesday is Mars. In Latin languages this is more obvious - for example, in Spanish (a handy reference, since it's similar to Latin and I speak it), Martes. English is based on the Anglo-Saxon/German equivalent, known as Tiw, another god of war. Wednesday, or Miercoles in Spanish, is Mercury (in German, Mittwoch, or midweek - there is an older connection to Woden or Odin). Thursday is Thor or Jupiter (Jueves in Spanish). Friday, Viernes, is Venus, or Freitag or Freya's day. Saturday invariably sounds like Sabbath or Saturn. All well and good, you probably knew some or all of that. But why do they come in that order?
Since all these "heavenly bodies" moved around in their "heavenly shells", they each crossed the background of apparently static stars and made a complete circuit of the heavens. It is easy to instinctively reject this as the Sun and Moon surely do that every 24 hours, except that that's a circuit of the sky - not the entire background of stars, for example starting in the constellation Taurus (to the right of Orion) and all the way around until they get back again. From that point of view they do it in a funny order: the Moon is fastest, then Mercury, then Venus, then the Sun, then Mars, then Jupiter, then Saturn. All right, some of those are in the order in which the planets are really spaced from the Sun. But not all.
But the weekdays don't follow that, or they'd go in the order of Monday, Wednesday, Friday, Sunday, Tuesday, Thursday, Saturday. And this is where the 24 hour timetable comes in.
Each "hour" is supposedly "controlled" by a planet or deity. For example, midnight on Monday is controlled by the Moon. Then after that we go to Saturn - the "god" who takes the longest time to cross the entire heavens (or ecliptic). Then Jupiter, the second-longest. Then Mars, and so on. The table at the bottom of this section shows the system, as does this table I wrote myself to see if it worked before I found that one:
. . . and so on. (The page ran out.)
Of course, one website - I now can't remember which - threw a spanner in the works by claiming that the Babylonians only had 12 hours, which stops the system working. Sources seem to differ as to whether or not they bought into astrology and predictions. On the one hand, one cites as 11th century writer as claiming that "predictions are a new science", and on the other, we've got this really detailed and prescriptive table of what all the hours are supposed to mean - for example, you should ask a lady out on a date during one of Venus's hours. (Detailed and prescriptive is also exactly how I would describe the ridiculously large array of different labels on homeopathic products, all of which basically just contain sugar.) All I can say is, if you ask me on a date at 6am on a Monday morning, I will not rush to my astrological chart and swoon obediently because of some arbitrary rule, I will wonder (unless we have been up all night talking for example) what the heck is going on!
Sadly, most of the websites I found, whilst trying to make some sense of this fascinating history of people who made such detailed records, were trashy horoscope sites, so do please indulge me and let me make a little bit of fun. Some of the discoveries ancient people made, as well as the time and care they took with compiling massive records, are really incredible achievements. Incidentally, just a few of those are what I'll be talking about at Cardiff Skeptics on Monday next week - I hope to see some of you then.