Days of the Week

 

 

Days of the week from the Roman period have been both named after the seven planets of classical astronomy and numbered, beginning with Sunday. In Slavic languages, a numbering system was adopted, but beginning with Monday. There was an even older tradition of names in Ancient Indian Astrology, which could arguably be the origin of all these naming systems. All of these systems have been adopted in many languages, with some exceptions resulting from a number of religious and secular considerations.

Between the 1st and 3rd centuries the Roman Empire gradually replaced the eight day Roman nundinal cycle with the seven-day week. The astrological order of the days was explained by Vettius Valens and Dio Cassius. According to these authors, it was a principle of astrology that the heavenly bodies presided, in succession, over the hours of the day. The Ptolemaic system asserts that the order of the heavenly bodies, from the farthest to the closest to the Earth, is: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon.

In astrological theory, not only the days of the week, but the hours of the day are dominated by the seven luminaries. If the first hour of a day is dominated by Saturn (Saturn), then the second hour is dominated by Jupiter (Jupiter), the third by Mars (Mars), and so on with the Sun (Sun), Venus (Venus), Mercury (Mercury), and the moon (Moon), so that the sequence of planets repeats every seven hours. Therefore, the twenty-fifth hour, which is the first hour of the following day, is dominated by the Sun; the forty-ninth hour, which is the first hour of the next day, by the Moon. Thus, if a day is labelled by the planet which dominates its first hour, then Saturn's day is followed by the Sun's day, which is followed by the Moon's day, and so forth.

According to Vettius Valens, the first hour of the day began at sunset, which follows Greek and Babylonian convention. He also states that the light and dark halves of the day were presided over by the heavenly bodies of the first hour of each half.