Saturnday, Sunday, Moonday


The ancient Greeks inherited the practice of astrology from the Babylonians, but introduced many new features.  For example, where the Babylonians tended not to place the major planets in any physically significant order, the Greeks ordinarily listed them on horoscopes like this



Even though they didn't have a heliocentric model of the solar system, they were still able to deduce the order of the planets, beginning from Saturn as the furthest out and descending to Mercury as the closest in, based on the their periods of their "wanderings" across the night sky.


On this list the Sun and Moon are placed somewhat arbitrarily at the beginning, since their apparent motions obviously aren't of the same nature as those of the planets.  It was also common for the Greeks to place the Moon last, so that it was considered to be even "lower" than Mercury.  In addition, the Greeks could distinguish between the "interior" planets (Venus, Mercury) and the "exterior planets (Saturn, Jupiter, Mars) based on their apparent motions, and they sometimes placed the Sun in the "center" between these groups.  This led to the arrangement



Now, each of the 24 hours (an Egyptian invention) of the day was though to be "ruled" by one of these 7 planets, and the rulers would cycle around in the arrangement shown above.  Thus, if we denote the planets by the symbols T,J,R,S,V,Y,M respectively, and begin the first day with the Sun, we have



    Day    1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4


     1     S V Y M T J R S V Y M T J R S V Y M T J R S V Y

     2     M T J R S V Y M T J R S V Y M T J R S V Y M T J

     3     R S V Y M T J R S V Y M T J R S V Y M T J R S V

     4     Y M T J R S V Y M T J R S V Y M T J R S V Y M T

     5     J R S V Y M T J R S V Y M T J R S V Y M T J R S

     6     V Y M T J R S V Y M T J R S V Y M T J R S V Y M

     7     T J R S V Y M T J R S V Y M T J R S V Y M T J R


After the 7th day the cycle repeats, so the 8th day is the same as the 1st, and so on.  (Fortunately, 7 is coprime to 24.)  Each day in the cycle was said to be "ruled" overall by the planet that rules the first hour of that day, so the rulers of the seven days were S,M,R,Y,J,V,T, which is to say



According to Neugebauer, this is also the arrangement of the planets that was used most often in Hindu astronomy.  From this we get the names of the days in the week


              Latin         French      Saxon        English


  Sun       Dies Solis     Dimanche    Sun's day      Sunday

  Moon      Dies Lunae     Lundi       Moon's day     Monday

  Mars      Dies Martis    Mardi       Tiw's day      Tuesday

  Mercury   Dies Mercurri  Mercredi    Woden's day    Wednesday

  Jupiter   Dies Jovis     Jeudi       Thor's day     Thursday

  Venus     Dies Veneris   Vendredi    Frigg's day    Friday

  Saturn    Dies Saturni   Samedi      Seterne's day  Saturday


Wodin (or Odin) was one of the principal gods in Scandinavian and Teutonic mythology, and he seems to have somehow become identified with the Roman Mercurius.  Likewise Tiw was identified with Mars.  Frigg was the wife of Odin, and likened to Venus.  The Germanic god Thor is similar to Jupiter, in the sense of being regarded as the "main" god in most northern European countries.  This shows how the common names for our days of the week have been influenced by a wide range of peoples and traditions, including the Babylonians (astrology), Egyptians (24 hour division of the day), Greeks (arrangement of the planets), Romans (Latin names of the gods), and Scandinavian mythology (for the Germanic names).


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