week

See also: numbering of weeks in the year

The week is the only unit of the calendar whose length is not an interval determined by the motion of the earth or the moon. It has been suggested that the length of the week reflects the interval between market days.

The seven-day week is established in the Old Testament (Genesis). For many families, it is still the interval between having to go grocery shopping.

Names of the days of the week

In many calendars the days of the week are simply numbered, or have names based on number names. The Jewish (except for the Sabbath) and French Republican calendars are examples.  The Quakers in colonial America refused to use day names with pagan roots, and referred to Thursday, for example, as the "fifth day."

Our present day names began in astrology during the Roman empire. Each day was associated with the “planet” that rules its first hour. In those pre-Copernican times, the seven “planets” were (in order of what was thought to be their distance from us) Saturn, Jupiter, Mars, the sun, Venus, Mercury and the moon. The first hour of the first day of the week was associated with Saturn, the second hour with Jupiter, and so on, the cycle beginning to repeat with the 8th hour. Since 24 (the number of hours of the day) isn't evenly divisible by 7, the 25th hour–the first hour of the second day–was associated with the sun. The table below, numbering the hours in a week, shows how they cycled through the “planets.” Red numbers indicate the first hour of a day.

Saturn 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 156 163
Jupiter 2 9 16 23 30 37 44 51 58 65 72 79 86 93 100 107 114 121 128 135 142 149 157 164
Mars 3 10 17 24 31 38 45 52 59 66 73 80 87 94 101 108 115 122 129 136 143 150 158 165
sun 4 11 18 25 32 39 46 53 60 67 74 81 88 95 102 109 116 123 130 137 144 151 159 167
Venus 5 12 19 26 33 40 47 54 61 68 75 82 89 96 103 110 117 124 131 138 145 152 160 168
Mercury 6 13 20 27 34 41 48 55 62 69 76 83 90 97 104 111 118 125 132 139 146 153 161  
Moon 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 162  

This gives the days of the week the order: Saturn, sun, moon, Mars, Mercury, Jupiter, Venus.

Later, under the influence of the Roman religion Mithraism, dies solis replaced dies Saturnis as the first day of the week, which incidentally made the day names more acceptable to Christians, who conducted their religious observances on Sunday and already considered it the first day of the week.

The day names based on planets were officially adopted by the Emperor Constantine in 321 ce.

The original Latin names are evident in the day names in languages derived from Latin (see the modern French names in the table below), but sometime before the 12th century, in some Northern European countries the Roman gods were replaced by Northern European counterparts. In Old English,

Roman
astro-
logical
Dies Solis
(Sun
day)
Dies Luna
(Moon
day)
Dies Martis
(Mars'
day)
Dies Mercurii
(Mercury's
day)
Dies 
(Jupiter's
day)
Dies
Veneris

(Venus'
day)
Dies Saturnis
(Saturn's day)
Modern French dimanche lundi mardi mercredi jeudi vendredi samedi
Old
English
sunnandœg mōnandœg tīwesdœg wödnesdœg thunresdœg frigedœg sœterndœg
Modern English Sunday Monday Tuesday Wednesday Thursday Friday Saturday

 

F. H. Colson.
The Week: An Essay on the Origin and Development of the Seven-day Cycle.
Cambridge: Cambridge University Press, 1926.

S. Gandz.
The origin of the planetary week or the planetary week in Hebrew literature.
Proceedings of the American Academy for Jewish Research, volume 18, pages 213-254. (1949)

Eviatar Zerubavel.
The Seven Day Circle.
New York: The Free Press, 1985.

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