

Astronomical reasons for a six day week - wslh
http://en.wikipedia.org/wiki/Carlos_Varsavsky#Six_day_week

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lutusp
But a more interesting alternative is a calendar of 13 four-week months for a
total of 364 days, plus one or two days, without systemic names or dates, that
are inserted during a year.

Each month has four weeks of seven days, 28 days altogether, 13 * 28 = 364.

Guess what the drawback is? If months and weeks start on canonical days (i.e.
1 and Sunday), every month has a Friday the 13th. :)

