Sunday In Vietnamese, the working days in the week are named as: "Thứ Hai" (second day), "Thứ Ba" (third day), "Thứ Tư" (fourth day), "Thứ Năm" (fifth day), "Thứ Sáu" (sixth day), "Thứ Bảy" (seventh day). Sunday is called "Chủ Nhật", a corrupted form of "Chúa Nhật" meaning "Lord's Day". Some colloquial text in the south of Vietnam and from the church may still use the old form to mean Sunday. In German, Wednesday is called "Mittwoch", literally "mid-week", implying that weeks run from Sunday to Saturday. In Italian, Sunday is called "domenica", which also means "Lord's Day" (from Latin "Dies
Eight-day week popularity of the seven-day rhythm won and the eight-day week disappeared. The cycle of seven days, named after the sun, the moon, and the five planets visible to the naked eye, was already customary in the time of Justin Martyr, who wrote of the Christians meeting on the Day of the Sun (Sunday). Emperor Constantine eventually established the seven-day week in the Roman calendar in AD 321. The Celts used periods of darkness such as night and winter to begin their calculations of time. This meant that the first period of time in a "week" was a night, followed by