page_title: Week
section_title: Days of the week
hierarchical_section_title: Week / Days of the week
context_page_description: A week is a time unit equal to seven days. It is the standard time period used for cycles of rest days in most parts of the world, mostly alongside—although not strictly part of—the Gregorian calendar.
  In many languages, the days of the week are named after classical planets or gods of a pantheon. In English, the names are Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday. Such a week may be called a planetary week. This arrangement is similar to a week in the Bible in which the seven days are simply numbered with the first day being a Christian day of worship and the seventh day being a sabbath day. The traditional Biblical sabbath is aligned with Saturday.
  While, for example, the United States, Canada, Brazil, Japan and other countries consider Sunday as the first day of the week, and while the week begins with Saturday in much of the Middle East, the international ISO 8601 standard has Monday as the first day of the week. The ISO standard includes the ISO week date system, a numbering system for weeks within a given year, where each week starting on a Monday is associated with the year that contains that week's Thursday.
context_section_description: The days of the week were originally named for the classical planets. This naming system persisted alongside an "ecclesiastical" tradition of numbering the days, in ecclesiastical Latin beginning with dominica (the Lord's Day) as the first day. The Greco-Roman gods associated with the classical planets were rendered in their interpretatio germanica at some point during the late Roman Empire, yielding the Germanic tradition of names based on indigenous deities.
  The ordering of the weekday names is not the classical order of the planets (by distance in the planetary spheres model, nor, equivalently, by their apparent speed of movement in the night sky). Instead, the planetary hours systems resulted in succeeding days being named for planets that are three places apart in their traditional listing. This characteristic was apparently discussed in Plutarch in a treatise written in c. AD 100, which is reported to have addressed the question of Why are the days named after the planets reckoned in a different order from the actual order? (the text of Plutarch's treatise has been lost).
  An ecclesiastical, non-astrological, system of numbering the days of the week was adopted in Late Antiquity. This model also seems to have influenced (presumably via Gothic) the designation of Wednesday as "mid-week" in Old High German (mittawehha) and Old Church Slavonic (срѣда). Old Church Slavonic may have also modeled the name of Monday, понєдѣльникъ, after the Latin feria secunda. The ecclesiastical system became prevalent in Eastern Christianity, but in the Latin West it remains extant only in modern Icelandic, Galician, and Portuguese.
caption: Schematic comparison of the ordering of the classical planets (arranged in a circle) and the sequence of days in the week (forming a {7/3} heptagram within the circle).
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