> I was trying to figure out why a week is 7 days and not some other division. The first chapter of Daniel Boorstin's The Discovers has an interesting history

> I was trying to figure out why a week is 7 days and not some other division. The first chapter of Daniel Boorstin's The Discovers has an interesting history of calendars and time-keeping. For the question of Why a seven-day week, start on page 13: http://books.google.com/books?id=aEr07wJ21NYC&lpg=PA13&vq=7%20days&pg=PA13#v=snippet&q=7%20days&f=false http://books.google.com/books?id=aEr07wJ21NYC&lpg=PA13&vq=7%... tl;dr The week varied among cultures, and the seven-day week was in use by the Romans by the third century. Each day of the week honored one of the seven "planets" (in the ancient use of the word, a wanderer in the sky): Sun Moon Mars Venus Mars Mercury Jupiter Venus and Saturn. Derivations of those words are still in use today.