Seven days is close to a quarter of a lunation, and several ancient calendars did divide the month that way — but the week eventually cut loose and started running independently.

A lunation is 29.53 days, so four exact weeks fall a day and a half short, and any culture that tried to keep them aligned had to insert stray days. Judaism let the week run continuously instead, and that decision spread with Christianity and Islam until the seven-day cycle became the one unit of time on Earth that is attached to nothing astronomical at all.