The days 101

Our names of the week are based on the Latin days of the week. The Romans had struggled to create an 8-day system, but eventually opted for the simpler Babylonian 7-day system which was quite common in the Near East beginning in the 3rd century B.C.. Interestingly enough, modern science has shown that the human body and other life forms follow a 7-day biorhythm.

The Babylonian days were named after their pantheon of gods (based on the earlier Sumerian pantheon). The Romans, then, simply substituted their own gods' names over the top of these: so Shamash, Sin, Nergal, Nabû, Ishtar, Marduk, Ninurta became Sol, Luna, Mars, Mercury, Jupiter (Jove), Venus and Saturn. More exactly, these were the names of the 7 known celestial bodies. The days were called:

dies solis - "day of the sun"
dies lunae - "day of the moon"
dies Martis - "day of Mars"
dies Mercurii - "day of Mercury"
dies Jovis - "day of Jupiter"
dies Veneris - "day of Venus"
dies Saturni - "day of Saturn"

Anyone familiar with astronomy should note that the Roman calendar days did not coincide with their planetary order (Saturn > Jupiter > Mars > Sun > Venus > Mercury > Moon). Instead the Roman-Babylonian system followed a specialized pattern: the days were divided up in 24 hour cycles with each god or goddess ruling over their consecutive hour. For example, Saturn ruled over the first hour of dies Saturni, followed by Jupiter over the second hour and so on. This would mean that the 23rd hour was Jupiter’s, the 24th hour was Mars’ and the 25th hour (the first hour of the next day) was the sun’s hour.

The Anglo-Saxons similarly substituted their pantheon for the Roman deity:

dies solis became sunnandæg
dies lunae became Mnandæg
dies Martis became Twesdæg (Tiu was the Germanic God of War)
dies Mercurii became Wdnesdæg (Woden is an alternate form of Odin)
dies Jovis became th'resdæg (Thor’s day; Thor, like Jove, was the god of thunder)
dies Veneris became Frgedæg (Frigg was Odin’s wife and the goddess of the heavens; also the Indo-European root pri- from which the name Frigg is formed, means to love)
dies Saturni became Sæternesdæg