Origin of the Seven-Day Week

Sunday was named after the Sun. Monday was named after the moon.
This page explains why the week has seven days and how each of them got its name.

A long time ago in human history, people thought that Earth was flat, and at the universe’s center. They believed that seven members of the solar system forever circled around us—see graphic to the right, or view one from Censorinus – Sur le jour natal.
Some Mediterranian peoples also believed that each hour of the day was ruled by either the Sun, Moon or one of five then-known planets, all of which were thought of as gods. The sequence in which they thought hours were governed was the inverse order of distance they believed those solar system objects to be from Earth.

During this time, Egyptians thought that the most distant was Saturn, shown at the bottom of the graphic above. They thought that the order of closer members (shown counterclockwise following Saturn) was Jupiter, Mars, Sun, Venus, Mercury and closest, the Moon. So they believed that the first hour was ruled by Saturn, the second by Jupiter and so on. 1
Egyptians also believed that after each seven hours the order in which these objects ruled was repeated, so it started again with Saturn.
According to those ancient Egyptians, the planet that ruled the first hour also governed the entire twenty-four hour period, and gave its name to that day. 2   The first (and also the 8th, 15th and 22nd) hours of the first day were sacred to Saturn, the 23rd to Jupiter, the 24th to Mars and the first hour of the next day to the Sun. Therefore, they believed that the first day was ruled by and named after Saturn (Saturday) and the second was ruled by (and named after) the Sun (Sunday). 3

Celsus claimed that the same doctrine was part of ‘Persian theology.’ 4 Six hundred years ago, Chaucer described this belief in his Treatise on the Astrolabe under the heading of Special declaracioun of the houres of planetes.5 Chaucer’s text was translated from a much earlier manuscript from Greece.
The distance that these sky gods were perceived to be from Earth is not the same as the order in which they were believed to have ruled days. This is easy to understand but difficult to visualize. If you care to see it shown in the form of a chart, select Hourly Cycle that Determined Day Names.
Egyptians once divided all twelve 30-day months (of their 360-day calendar year) into three 10-day weeks in the same manner as Greeks of the same period. 6   The epoch at which planet worship caused them to change its length to seven days is not known, but it must have been over twenty-five hundred years ago because Herodotus, writing in his History during the 5th century B.C. said: “Here are some other discoveries of the Egyptians. They find…each day belongs to a god…” 7
Adherents of the cult of Sin at Harran, who were known as Harranians or Sabeans by Arabic and Syrian authors, named their days after the same solar system members 8 as Egyptians and Persians. Like Hebrews and many other peoples, they considered the one named after Saturn to be the seventh day, so they began their week with a day named after the Sun. All seven days were named after solar system members in the same order as they were in Egypt.
It is interesting to note that these exact same solar system objects, and in the same sequence, were also used to name days in ancient India, Tibet and Burma. 9   This is also true of names for Japanese days of the week, but the custom there has been traced back only a thousand years. 10
Roman soldiers stationed in Egypt became accustomed to the pagan seven-day week and began to introduce it into their own homeland to replace their eight-day marketing week. Octavian (Caesar Augustus) and succeeding Roman rulers permitted this practice but it wasn’t made official until the emperor Constantine took that step in A.D. 321.
English names for days of the week are derived from Anglo-Saxon names for those same seven heavenly bodies that were revered by ancient peoples. Compare those English and Anglo-Saxon day names in the table below. Other similarities between day and “planet” names in various countries can be observed there.

Solar System Objects and Some of Their Various Day or “Planet” Names

  Sun Moon Mars Mercury Jupiter Venus Saturn
English Day Name
Anglo-Saxon Day Name
Sunnan daeg
Monan daeg
Tiwes daeg
Wodens daeg
Thurs daeg
Frige daeg
Satern daeg
German Day Name
Dutch Day Name
French Day Name
Latin Day Name
Dies Solis
Dies Lunae
Dies Martis
Dies Mercurii
Dies Jovis
Dies Veneris
Dies Saturni
Hindu Day Name
Vrihaspat-var or Guru-var
Sani-var/ Sanichar
Indian Islam Day Name
Peer or Somwar
Burmese Day Name
Tanang- ganve
Tanang- la
Buddha- hu
Kyasa- pade
Sabean “Planet”
Bel Marduk
Japanese “Planet” 11
Japanese Day Name
Nichi Youbi
Getsu Youbi
Ka Youbi
Sui Youbi
Moku Youbi
Kin Youbi
Dou Youbi

Note the German day name of “Mittwoch” instead of “Mercury Day.” This came about because sometime around A.D. 1020 a Monk named Notker coined the term in mittauuechun (in the middle of the week) as a substitute for using the pagan god Mercury’s name. 12
There’s an alternate explanation for how the same heavenly objects came to be used to name days of the week in their present order. It assumes that the sequence of hours dedicated to these sky gods resulted from the length of their orbital periods in Earth-days. 13 But this would have required using Earth’s year in place of a value for the Sun, and lunation’s instead of the Moon’s yearly period. It also requires “planetary leaps,” skipping two planets at a time when assigning day names, all very improbable procedures.


1. Macrone, Michael. By Jove! New York: Cader Books, 1992. pp. 209-211.
2. Catholic Encyclopedia: SUNDAY (8KB)
3. Macrone. op. cit., p. 210.
4. Bickerman, Elias Joseph. Chronology of the Ancient World.
Ithica, N.Y.: Cornell University Press, 1968. p. 59.
5. Chaucer, Geoffrey. A Treatise on the Astrolabe. (81KB). c. 1391. Part II-12.
or Special Declaracioun of the Houres of Planetes. (2KB).
6. Goudsmit, Samuel A. Time.
New York, Time Incorporated, 1966. p. 24.
7. Herodotus. The History. (5th century B.C.) 2.82.
8. Langdon, Stephen Herbert. The Mythology of all Races: Semitic.
New York: Cooper Square Publishers, Inc., 1964. p. 154.
9. Parise, Frank. The Book of Calendars.New York: Facts On File, Inc. p. 172.
10. Renshaw, Steven L. The Solar System and Names for Days.
11. Renshaw, Steven L. ibid.
12. Borst, Arno. The Ordering of Time.
Chicago: The University of Chicago Press, 1993. pp. 60-61.
13. Zerubavel, Eviatar. The Seven Day Circle.
Chicago: The University of Chicago Press, 1985. pp. 14-17.