Names of the days of the week
In many languages, the names given to the seven days of the week are derived from the names of the classical planets in Hellenistic astronomy, which were in turn named after contemporary deities, a system introduced by the Roman Empire during Late Antiquity. In some other languages, the days are named after corresponding deities of the regional culture, beginning either with Sunday or with Monday. The seven-day week was adopted in early Christianity from the Hebrew calendar, and gradually replaced the Roman nundinal cycle as the new religion spread. Sunday remained the  first day of the week, being considered the Lord's Day, while the Jewish sabbath remained the seventh. Emperor Constantine adopted the seven-day week for official use in CE 321, making the Day of the Sun () a legal holiday. In the international standard ISO 8601, Monday is treated as the first day of the week. Days named after planets. Greco-Roman tradition. Between the 1st and 3rd centuries AD, the Roman Empire gradually replaced the eight-day Roman nundinal cycle with the seven-day week. The earliest evidence for this new system is a Pompeiian graffito referring to 6  February ("ante diem viii idus Februarias") of the year AD 60 as "dies solis" ("Sunday"). Another early witness is a reference to a lost treatise by Plutarch, written in about AD 100, which addressed the question of: "Why are the days named after the planets reckoned in a different order from the 'actual' order?". (The treatise is lost, but the answer to the question is known; see planetary hours). The Ptolemaic system of planetary spheres asserts that the order of the heavenly bodies, from the farthest to the closest to the Earth is: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon , or, objectively, the planets are ordered from slowest to fastest moving as they appear in the night sky. The days were named after the planets of Hellenistic astrology, in the order: Sun, Moon, Mars ("Ares"), Mercury ("Hermes"), Jupiter ("Zeus"), Venus ("Aphrodite") and Saturn ("Cronos"). The seven-day week spread throughout the Roman Empire in Late Antiquity. By the 4th century, it was in wide use throughout the Empire, and it had also reached India and China. The Greek and Latin names are as follows: Romance languages. Except for Modern Portuguese and Mirandese, the Romance languages preserved the Latin names, except  for the names of Sunday, which was replaced by "[dies] Dominicus (Dominica)", i.e. "the Lord's Day", and of Saturday, which was named for the Sabbath. Mirandese and Modern Portuguese use numbered weekdays (see below), but retain "sábado" and "demingo"/"domingo" for weekends. Celtic languages. Early Old Irish adopted the names from Latin, but introduced separate terms of Norse origin for Wednesday, Thursday and Friday, then later supplanted these with terms relating to church fasting practices. Adoptions from Romance. Albanian adopted the Latin terms for Tuesday, Wednesday and Saturday, adopted translations of the Latin terms for Sunday and Monday, and kept  native terms for Thursday and Friday. Other languages adopted the week together with the Latin (Romance) names for the days of the week in the colonial period. Several constructed languages also adopted the Latin terminology. With the exception of "sabato", the Esperanto names are all from French, cf. French "dimanche, lundi, mardi, mercredi, jeudi, vendredi". Germanic tradition. The Germanic peoples adapted the system introduced by the Romans by substituting the Germanic deities for the Roman ones (with the exception of "Saturday") in a process known as . The date of the introduction of this system is not known exactly, but it  must have happened later than AD 200 but before the introduction of Christianity during the 6th to 7th centuries, i.e., during the final phase or soon after the collapse of the Western Roman Empire. This period is later than the Common Germanic stage, but still during the phase of undifferentiated West Germanic. The names of the days of the week in North Germanic languages were not calqued from Latin directly, but taken from the West Germanic names. Hindu tradition. Hindu astrology uses the concept of days under the regency of a planet under the term "vāsara", the days of the  week being called "āditya-, soma-, maṅgala-, budha-, guru-, śukra-," and "śani-vāsara". "śukrá" is a name of Venus (regarded as a son of Bhṛgu); "guru" is here a title of Bṛhaspati, and hence of Jupiter; "budha" "Mercury" is regarded as a son of "Soma", i.e. the Moon. Knowledge of Greek astrology existed since about the 2nd century BC, but references to the "vāsara" occur somewhat later, during the Gupta period ("Yājñavalkya Smṛti", c. 3rd to 5th century), i.e. at roughly the same period the system was introduced in the Roman Empire. Southeast Asian languages. The Southeast Asian tradition also uses  the Hindu names of the days of the week. Hindu astrology adopted the concept of days under the regency of a planet under the term "vāra", the days of the week being called "āditya-, soma-, maṅgala-, budha-, guru-, śukra-," and "śani-vāra". "śukrá" is a name of Venus (regarded as a son of Bhṛgu); "guru" is here a title of Bṛhaspati, and hence of Jupiter; "budha" "Mercury" is regarded as a son of "Soma", i.e. the Moon. East Asian tradition. The East Asian naming system for the days of the week closely parallels that of the Latin system and is  ordered after the "Seven Luminaries" (七曜 "qī yào"), which consists of the Sun, Moon and the five planets visible to the naked eye. The Chinese had apparently adopted the seven-day week from the Hellenistic system by the 4th century, although by which route is not entirely clear. It was again transmitted to China in the 8th century by Manichaeans, via the country of Kang (a Central Asian polity near Samarkand). The 4th-century date, according to the "Cihai" encyclopedia, is due to a reference to Fan Ning (范寧), an astrologer of the Jin Dynasty. The renewed adoption from Manichaeans  in the 8th century (Tang Dynasty) is documented with the writings of the Chinese Buddhist monk Yijing and the Ceylonese Buddhist monk Bu Kong. The Chinese transliteration of the planetary system was soon brought to Japan by the Japanese monk Kobo Daishi; surviving diaries of the Japanese statesman Fujiwara no Michinaga show the seven-day system in use in Heian Period Japan as early as 1007. In Japan, the seven-day system was kept in use (for astrological purposes) until its promotion to a full-fledged (Western-style) calendrical basis during the Meiji era. In China, with the founding of  the Republic of China in 1911, Monday through Saturday in China are now named after the luminaries implicitly with the numbers. Numbered days of the week. Days numbered from Monday. The ISO prescribes Monday as the first day of the week with ISO-8601 for software date formats. The Slavic, Baltic and Uralic languages (except Finnish and partially Estonian and Võro) adopted numbering but took Monday rather than Sunday as 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" ("вторник") "Tuesday" and "vtoroj" ("второй") "the second", "chetverg" ("четверг") "Thursday" and "chetvjortyj" ("четвёртый") "the fourth", "pyatnitsa" ("пятница") "Friday" and "pyatyj" ("пятый") "the fifth"; see also the Notes. In Standard Chinese, the week is referred to as the "Stellar Period" () or "Cycle" (). The modern Chinese names for the days of the week are based on a simple numerical sequence. The word for "week" is followed by a number indicating the day: "Monday" is literally the "Stellar Period One"/"Cycle One", i.e. the "First day of the Stellar Period/Cycle", etc. The exception is Sunday, where 日 ("rì ), day" or "Sun", is used instead of a number. A slightly informal and colloquial variant to 日 is 天 ("tiān") "day", "sky" or "heaven". Accordingly, the notational abbreviation of the days of the week uses the numbers, e.g. 一 for "M" or "Mon(.)", "Monday". Note that the abbreviation of Sunday uses exclusively 日 and not 天. Attempted usage of 天 as such will not be understood. Colloquially, the week is also known as the "Prayer" (), with the names of the days of the week formed accordingly. The following is a table of the Mandarin names of the days of the  weeks. Note that standard Taiwan Mandarin pronounces 期 as "qí", so 星期 is instead "xīngqí". While all varieties of Mandarin may pronounce 星期 as "xīngqi" and 禮拜/礼拜 as "lǐbai", the second syllable with the neutral tone, this is not reflected in the table either for legibility. Days numbered from Sunday. Sunday comes first in order in calendars shown in the table below. In the Abrahamic tradition, the first day of the week is Sunday. Biblical Sabbath (corresponding to Saturday) is when God rested from , making the day following the Sabbath the first day of the week (corresponding to Sunday ). Seventh-day Sabbaths were sanctified for celebration and rest. After the week was adopted in early Christianity, Sunday remained the first day of the week, but also gradually displaced Saturday as the day of celebration and rest, being considered the Lord's Day. Saint Martin of Dumio (c. 520–580 [10520–10580]), archbishop of Braga, decided not to call days by pagan gods and to use ecclesiastic terminology to designate them. While the custom of numbering the days of the week was mostly prevalent in the Eastern Church, Portuguese, Mirandese and Galician, due to Martin's influence, are the only Romance languages  in which the names of the days come from numbers rather than planetary names. Members of the Religious Society of Friends (Quakers) historically objected to the pagan etymologies of days and months and substituted numbering, beginning with First Day for Sunday. Icelandic is a special case within the Germanic languages, maintaining only the Sun and Moon ("sunnudagur" and "mánudagur" respectively), while dispensing with the names of the explicitly heathen gods in favour of a combination of numbered days and days whose names are linked to pious or domestic routine ("föstudagur", "Fasting Day" and "laugardagur", "Washing Day"). The "washing day" is  also used in other North Germanic languages, but otherwise the names correspond to those of English. Days numbered from Saturday. In Swahili, the day begins at sunrise, unlike in the Arabic and Hebrew calendars where the day starts at sunset (therefore an offset of twelve hours on average), and unlike in the Western world where the day starts at midnight (therefore an offset of six hours on average). Saturday is therefore the first day of the week, as it is the day that includes the first night of the week in Arabic. Etymologically speaking, Swahili has two "fifth" days. The  words for Saturday through Wednesday contain the Bantu-derived Swahili words for "one" through "five". The word for Thursday, "Alhamisi", is of Arabic origin and means "the fifth" (day). The word for Friday, "Ijumaa", is also Arabic and means (day of) "gathering" for the Friday noon prayers in Islam. Mixing of numbering and astronomy. In the Žejane dialect of Istro-Romanian, "lur" (Monday) and "virer" (Friday) follow the Latin convention, while "utorek" (Tuesday), "sredu" (Wednesday), and "četrtok" (Thursday) follow the Slavic convention. There are several systems in the different Basque dialects. In Judaeo-Spanish (Ladino), which is mainly based on  a medieval version of Spanish, the five days of Monday–Friday closely follow the Spanish names. Sunday uses the Arabic name, which is based on numbering, because a Jewish language was not likely to adapt a name based on "Lord's Day" for Sunday. As in Spanish, the Ladino name for Saturday is based on "Sabbath". However, as a Jewish language—and with Saturday being the actual day of rest in the Jewish community—Ladino directly adapted the Hebrew name, "Shabbat". The days of the week in the Bishnupriya Manipuri and Meitei languages originate from the Sanamahi creation myth. Notes . Sunday. From Latin () or Greek () Monday. After No Work Tuesday. Thing (Assembly), of which god Tyr/Ziu was the patron. Wednesday. Mid-week "or" Middle Thursday. The day between two fasts ("An Dé idir dhá aoin", contracted to "An Déardaoin") (Christianity) Friday. The Fast or Fasting Day (Christianity) Good Friday or Preparation (Christianity) Or canàbara, cenàbara, cenàbera, cenàbura, cenarba, chenàbara, chenabra, chenapra, chenàpura, chenarpa, chenàura, cianàbara, chenabura; meaning holy supper as preparation to the sabbathday(saturday) Saturday. "Shabbat" (Jewish and Christian Sabbath)