The oldest scheduling system still in daily use. You say its output every time you say Thursday.
How to read it
This maps the system as a sequence: the order of the seven, the hours, the arithmetic that produced the week, and where it survives. It's history and timing — never prediction.
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1 of 5
The order
Saturn to Moon
Slowest to fastest.
Seven bodies ranked by how slowly they seem to move: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. Everything else follows from this order.
2 of 5
The hours
Planetary hours
Each hour has its ruler.
Daylight and night are each divided into twelve unequal hours, ruled in that repeating order. A planetary hour stretches in summer and shrinks in winter.
3 of 5
The arithmetic
Twenty-four by seven
Three steps a day.
The first hour gives a day its name. Twenty-four hours through a cycle of seven lands three places on, so the days run Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn.
4 of 5
The use
Picatrix, Agrippa
Timing, not fortune.
Magical manuals timed their work by the clock — a Venus hour for tenderness, a Mercury hour for writing. It answered when, never what will happen.
5 of 5
What survives
Vara, hora
In plain sight.
The names hold in English, in French — mardi, mercredi, jeudi, vendredi — in Japanese, and in the Hindu seven-day vara, which follows the same sequence.
Whatever you make of it, the week is its residue.
Hellenistic astronomy. The 'Chaldean' label is Macrobius's; historians find no trace of it in Babylonian astrology.