Discover how the days of the week got their names from Norse gods, Roman deities, and planetary bodies. Last reviewed on 2026-05-09 The Seven-Day Week: A Brief History The concept of a seven-day week is one of humanity's oldest methods of organizing time, with roots stretching back to ancient Mesopotamia. This division of time has survived for thousands of years across multiple civilizations, eventually becoming standardized worldwide. But why seven days specifically, and how did each day get its name? The seven-day structure likely originated from observations of celestial bodies. Early astronomers identified seven "planets" visible to the naked eye: the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn. These seven heavenly bodies, which appeared to move independently against the fixed stars, formed the basis for dividing the lunar month into roughly four seven-day periods. As this timekeeping system spread across cultures, each civilization adapted it according to their own deities, languages, and astronomical understanding. The result is a fascinating etymological tapestry that reveals connections between celestial observation, mythology, and linguistic evolution. For the deeper question — why seven specifically, and not five, eight, or ten — see why are there seven days in a week? . For how those seven days are organised today, including which one starts the week in different countries, see our country-by-country guide to the first day of the week . And for languages that don't name their days at all but number them instead, see numbered days vs. named days . Modern weekend conventions — Saturday and Sunday off in much of the world, but Friday-Saturday in others — are a much newer overlay on this ancient cycle, traced in our short history of the weekend . Babylonian Origins Ancient Babylonians established a seven-day cycle based on celestial bodies. Each day was associated with one of the seven known "planets": Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Romans adopted the seven-day week and planetary naming system, creating dies Solis (Sun's day), dies Lunae (Moon's day), dies Martis (Mars' day), dies Mercurii (Mercury's day), dies Iovis (Jupiter's day), dies Veneris (Venus' day), and dies Saturni (Saturn's day). Germanic Adaptation Germanic peoples adopted the Roman system but substituted their own gods for the Roman deities where equivalents existed. This created the foundation for modern English day names. Christian Influence As Christianity spread, attempts were made to rename pagan-named days. While most languages retained planetary/god names, some changes occurred, particularly for Saturday (Sabbath) and Sunday (Lord's Day) in some languages. The Planetary Connection The relationship between days of the week and celestial bodies forms the foundation of weekday naming across many cultures. The seven visible "planets" of ancient astronomy (including the Sun and Moon) were assigned to the seven days in a specific order based on their perceived distance from Earth. The Planetary Week Order The original ordering of planets in the Babylonian system was: Saturn, Sun, Moon, Mars, Mercury, Jupiter, and Venus. However, the ordering of the days of the week follows a different pattern, derived from what's known as the "planetary hours" system. In this ancient astrological concept, each hour of the day was ruled by a planet, following the order of their assumed distance from Earth (Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon). The day was named after the planet that ruled its first hour. Following this system and rotating through all 24 hours of the day created the familiar weekly sequence we use today. Planetary Hour Sequence Explained Starting with Saturn ruling the first hour of day 1: Hour 1: Saturn (day is named after Saturn → Saturday) Hours 2-24: Each ruled by successive planets Hour 25 (first hour of next day): Sun (day is named after Sun → Sunday) This system produces the weekly sequence: Saturn, Sun, Moon, Mars, Mercury, Jupiter, Venus. This planetary sequence remains clearly visible in Romance languages. For example, in French, the days are: lundi (Moon), mardi (Mars), mercredi (Mercury), jeudi (Jupiter), vendredi (Venus), samedi (Saturn), and dimanche (originally dies dominicus or "Lord's day," replacing dies Solis). Norse Gods and English Weekday Names The English names for the days of the week represent a fascinating blend of Roman and Germanic influences. While the Romans used a straightforward planetary naming system, the Germanic peoples (including Anglo-Saxons) substituted their own gods for the Roman deities when they adopted the seven-day week. These substitutions were made based on perceived similarities between the Roman gods and Germanic deities, creating the unique naming pattern we see in modern English: The Norse Gods Behind the Days Tyr (also known as Tiu in Old English) was the Norse god of war, law, and honor, equivalent to the Roman Mars. Originally more important in the Germanic pantheon, he was later overshadowed by Odin and Thor. In Norse mythology, Tyr sacrificed his hand to the wolf Fenrir, demonstrating his association with bravery and sacrifice. Tuesday derives from "Tyr's day" (Old English: Tiwesdæg). Odin/Woden (Wednesday) Odin (called Woden by Anglo-Saxons) was the chief deity of the Norse pantheon, associated with wisdom, poetry, death, divination, and magic. He was often depicted as a wanderer with one eye, having sacrificed the other for wisdom. The Romans equated him with Mercury due to his role as a psychopomp (guide of souls) and his cleverness. Wednesday comes from "Woden's day" (Old English: Wōdnesdæg). Thor (Thursday) Thor was the immensely popular Norse god of thunder, lightning, storms, strength, and protection of mankind. Wielding his mighty hammer Mjölnir, Thor was the defender of Asgard and humankind against the giants. The Romans equated him with Jupiter/Jove, as both were thunder gods and powerful sky deities. Thursday derives from "Thor's day" (Old English: Þūnresdæg). Frigg/Freya (Friday) There's some ambiguity about whether Friday is named after Frigg (Odin's wife and goddess of motherhood and marriage) or Freya (goddess of love, beauty, and fertility). Both goddesses share similarities with the Roman Venus. Scholars debate which goddess the day was originally named for, and the two deities may have merged in some contexts. Friday comes from "Frigg's day" or "Freya's day" (Old English: Frīgedæg). Cultural Variations in Weekday Names While the planetary/deity system forms the basis for day names in many Indo-European languages, different cultures have developed their own approaches to naming the days of the week. Romance Languages: Clear Planetary Connections Romance languages derived from Latin maintain the clearest connection to the original Roman planetary system: *Note: Saturday and Sunday in Romance languages show Christian influence, with references to the Sabbath and the Lord's Day replacing the original planetary names in many cases. East Asian Numbering System

East Asian languages like Japanese, Korean, and Chinese use a straightforward numbering system mixed with planetary/elemental associations: Japanese Days of the Week Monday: 月曜日 (getsuyōbi) — "Moon day" Tuesday: 火曜日 (kayōbi) — "Fire (Mars) day" Wednesday: 水曜日 (suiyōbi) — "Water (Mercury) day" Thursday: 木曜日 (mokuyōbi) — "Wood (Jupiter) day" Friday: 金曜日 (kin'yōbi) — "Gold/metal (Venus) day" Saturday: 土曜日 (doyōbi) — "Earth (Saturn) day" Sunday: 日曜日 (nichiyōbi) — "Sun day" These East Asian names show a fascinating blend of the planetary associations with the five elements of Chinese philosophy (fire, water, wood, metal, earth), demonstrating how the planetary week was adapted to fit local cosmological systems. Numerical Systems Some languages use a numerical approach to naming weekdays. Portuguese partially uses this system, with second-feira (Monday) through sexta-feira (Friday), while retaining sábado (Saturday) and domingo (Sunday). Similarly, in Greek, the days are named for their liturgical significance, with Monday through Friday named as "Second" through "Sixth" days, while Saturday is Savvato (Sabbath) and Sunday is Kyriaki (Lord's day). Religious Influences on Weekday Names As major religions spread across cultures, they often influenced the naming of days, particularly the weekend days that held special religious significance. Judeo-Christian Influence The Jewish Sabbath (seventh day of rest) influenced the name for Saturday in many languages: Hebrew: שַׁבָּת (Shabbat) Italian: sabato Spanish: sábado Arabic: السبت (as-sabt) Christianity's designation of Sunday as the Lord's Day appears in many languages: Latin: dies dominicus ("Lord's day") Italian: domenica Spanish: domingo Greek: Κυριακή (Kyriaki, "Lord's [day]") Islamic Influence In Arabic and some languages influenced by Islam, days are numbered from Sunday, with Friday (the day of congregational prayer) given special status: Friday: الجمعة (al-Jumu'ah, "the gathering") Saturday: السبت (as-Sabt, from Hebrew "Sabbath") Sunday: الأحد (al-Aḥad, "the first") Monday: الإثنين (al-Ithnayn, "the second") Tuesday: الثلاثاء (ath-Thulatha', "the third") Wednesday: الأربعاء (al-Arbi'a', "the fourth") Thursday: الخميس (al-Khamis, "the fifth") Frequently Asked Questions About Day Names Who named the days of the week? The seven-day week and the naming system for days evolved gradually across multiple civilizations. Babylonians established the seven-day structure based on celestial bodies. Romans formalized a planetary naming system that spread throughout their empire. Germanic peoples later adapted the Roman system, substituting their own gods for Roman deities where equivalents existed. No single person or group "invented" the days of the week; rather, they developed organically across cultures and were gradually standardized through cultural exchange. What are the days of the week named after? In English, the days of the week are named after a combination of Germanic/Norse gods and celestial bodies: Sunday (Sun), Monday (Moon), Tuesday (Tiu/Tyr, Norse god of war), Wednesday (Woden/Odin, chief Norse deity), Thursday (Thor, Norse god of thunder), Friday (Frigg/Freya, Norse goddess), and Saturday (Saturn, Roman god). This pattern combines the Roman planetary week with Germanic deity substitutions. Other languages may follow different patterns, such as the straightforward planetary system seen in Romance languages, or numerical systems in Portuguese and other languages. How did the days of the week get their names? The naming of weekdays began with the Babylonian association of days with celestial bodies. Romans formalized this into a planetary week: dies Solis (Sun), dies Lunae (Moon), dies Martis (Mars), dies Mercurii (Mercury), dies Iovis (Jupiter), dies Veneris (Venus), and dies Saturni (Saturn). When this system spread to Germanic peoples, they substituted their own equivalent deities for the Roman gods, creating the basis for modern English names. Meanwhile, religious influences altered some day names, particularly Saturday (from Sabbath) and Sunday (Lord's Day) in many languages. The process was one of cultural adaptation rather than direct translation. Where did the names of the days of the week come from? The names of the days of the week originated from ancient astronomical observations. The seven visible "planets" of ancient astronomy (Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn) were associated with days in a specific order. This planetary week spread from Babylonia to Greece and Rome, then throughout Europe. Germanic peoples adapted the Roman system by substituting their own gods where cultural equivalents existed. For example, the Norse god Thor replaced Jupiter for Thursday, while Woden (Odin) replaced Mercury for Wednesday. This complex cultural exchange between Babylonian astronomy, Roman religion, Germanic mythology, and later Christian influence created the diverse naming patterns we see across languages today.