Thursday "xoves" and Romanian "joi". This is also reflected in the p-Celtic Welsh "dydd Iau". The astrological and astronomical sign of the planet Jupiter (♃) is sometimes used to represent Thursday. Since the Roman god Jupiter was identified with Thunor (Norse Thor in northern Europe), most Germanic languages name the day after this god: "Torsdag" in Danish, Norwegian, and Swedish, "Hósdagur"/"Tórsdagur" in Faroese, "Donnerstag" in German or "Donderdag" in Dutch. Finnish and Northern Sami, both non-Germanic (Uralic) languages, uses the borrowing "Torstai" and "Duorastat". In the extinct Polabian Slavic language, it was "perundan", Perun being the Slavic equivalent of Thor. There
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