Names of the days of the week the "first day". This convention is also found in some Austronesian languages whose speakers were converted to Christianity by European missionaries. In Slavic languages, some of the names correspond to numerals after Sunday: compare Russian "vtornik" "Tuesday" and "vtoroj" "the following", "chetverg" "Thursday" and "chetvertyj" "the fourth", "pyatnitsa" "Friday" and "pyatyj" "the fifth"; see also the Notes. In Standard Chinese, the week is referred to as the cycle of the stars (). The modern Chinese names for the days of the week are based on a simple numerical sequence. The word for "week" (which is literally translated to "star day")
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