> 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:
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.
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%...
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.