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period of time shorter than the month, commonly seven days. The ancient Egyptians used a 10-day period, as did the French under the short-lived French Revolutionary calendarFrench Revolutionary calendar,
the official calendar of France, Nov. 24, 1793–Dec. 31, 1805. Its introduction was decreed by the Convention on Oct. 5, 1793, but it was computed from Sept. 22, 1792, the autumnal equinox and the day after the proclamation of the republic.
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. In many regions a four-day to eight-day market week is based on the recurrence of market days; the early Romans observed an eight-day market week. This period also corresponds roughly with the moon's quarter phases, which come every seven or eight days. The seven-day week is said to have originated in ancient times in W Asia, probably in Mesopotamia. This is thought to have been a planetary week predicated on the astrological concept of the influence of the planets, which were long erroneously believed to be seven celestial bodies revolving around the earth; these were the sun and moon and five of the bodies recognized today as planets—Mars, Mercury, Jupiter, Venus, and Saturn. The Hebrew week is based chiefly on the religious observance of the SabbathSabbath
[Heb.,=repose], in Judaism, last day of the week (Saturday), observed as a rest day for the twenty-five hours commencing with sundown on Friday. In the biblical account of creation (Gen. 1) the seventh day is set as a Sabbath to mark God's rest after his work.
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, which comes every seventh day and is usually associated with the seventh day of creation, when the Lord rested from his labors. The Christian week and the Muslim week were probably derived chiefly from the Hebrew week, although the weekly holy days are different (Hebrew, Sabbath, seventh day; Christian, Sunday, first day; Muslim, Friday, sixth day). The influence of the weeks of Chaldaeans, Christians, and Jews slowly made itself felt in the Roman Empire, and elements of the systems were probably merged. The planetary week was at first preeminent, and the use of planetary names, based on names of pagan deities, continued even after Constantine (c.321) made the Christian week, beginning on Sunday, official in the civil calendar. The Roman names for the days of the week pervaded Western Europe; in most languages the forms are translations from Latin or attempts to assign corresponding names of divinities. The Latin names, their translations, the English equivalents, and their derivations follow: dies solis [sun's day], Sunday; dies lunae [moon's day], Monday [moonday]; dies Martis [Mars' day], Tuesday [Tiw's day]; dies Mercurii [Mercury's day], Wednesday [Woden's day]; dies Jovis [Jove's or Jupiter's day], Thursday [Thor's day]; dies Veneris [Venus' day], Friday [Frigg's day]; and dies Saturni [Saturn's day], Saturday.



a seven-day period with each day named differently. A seven-day week first came into use in the ancient East. In the first century A.D., this type of week was introduced in Rome and subsequently spread through all of Western Europe. Each day of the week was designated by a different name, derived from the names of seven heavenly bodies. Thus, Saturday was called Saturn’s day, and the days following it were called, respectively, the days of the sun, the moon, Mars, Mercury, Jupiter, and Venus. In the languages of Western Europe, these names are still partially preserved.

In Slavic languages, most names of days indicate the position of the day in the week with respect to Sunday, which in many Slavic languages is called nedelia, the day on which people ne delaiut (do not work). Thus, Monday is ponedel’nik (the day after nedelia), Tuesday is vtornik (the second day), and so on.

Some peoples adopted a division of time into five-day and ten-day weeks, such as the ten-day weeks (decades) of the ancient Egyptians. Decades were also used in the calendar adopted during the French Revolution.

For any date of the 20th century, the day of the week can be found from Tables 1 and 2, which constitute a perpetual calendar. The number denoting the year is divided by 28, and the remainder is noted. For the months of March through December, this remainder itself is used, whereas for January and February, the remainder is reduced by 1. Table 1 then yields a number ƞ for a given remainder. To determine the date of one of the Sundays in a particular month, the number m corresponding to this month is found from Table 2 and added to the previously found number n. The day of the week for a given date can then be easily found.

Table 1Table 2 
1 ..........515 ..........2January ..........2
2 ..........416 ..........7February ..........6
3 ..........317 ..........6March ..........0
4 ..........118 ..........5April ..........4
5 ..........719 ..........4May ..........2
6 ..........620 ..........2June ..........6
7 ..........521 ..........1July ..........4
8 ..........322 ..........7August ..........1
9 ..........223 ..........6September ..........5
10 ..........124 ..........4October ..........3
11 ..........725 ..........3November ..........0
12 ..........526 ..........2December ..........5
13 ..........427 ..........1  
14 ..........328 or 0 ..........6  

For instance, suppose we wish to find the day of the week for the date Feb. 23, 1975. Dividing 1975 by 28, we get a remainder of 15. Subtracting 1 from this remainder and consulting Table 1, we obtain n ═ 3. In Table 2, February corresponds to m ═ 6. Addition of ƞ and m shows that one of the Sundays in February 1975 was on the 9th of the month. Therefore, Feb. 23, 1975, also fell on a Sunday. (Table 1 has been compiled for dates of the 20th century using the New Style calendar.)


A time period of 7 days which has been accepted from ancient Babylon; the 7 days of the week were first given names of the seven celestial bodies: the sun, moon, and five visible planets.
References in classic literature ?
There were weeks at a time when Jurgis went home after such a day as this with not more than two hours' work to his credit--which meant about thirty- five cents.
Your woman has a gown, and her whole seven weeks wages are gone; ours has a gown, and two days' wages left, to buy something else with.
And now the April showers were dry-- The five short weeks were nearly spent-- Yet still he got the old reply,
Yes, I came hither to converse confidentially with General Monk, and ask him for an answer regarding certain interests; yes, the general being, doubtless, unable to pronounce before the expected battle, begged me to remain a week in the house I inhabit, promising me that in a week I should see him again.
I doubt,' said Mr Galloway, meditatively, 'if I shall be able to find time till the end of the week.
By the end of August, when Weeks returned from South Germany, Philip was completely under Hayward's influence.
He said they would do him for the whole week at two pounds five.
Three weeks before the time for the opening of the term at Hampton, I was pleasantly surprised to receive a letter from my good friend Miss Mary F.
Four weeks had passed since Pierre had been taken prisoner and though the French had offered to move him from the men's to the officers' shed, he had stayed in the shed where he was first put.
You want to know," he repeated meditatively, "on what terms I'll hold my tongue for a week.
About our little party down in Hampshire next week," he began.
He's paid for a week and we're jolly glad to get visitors at all these times.