Resources / Celestial timing
Planetary Day Calculator
A day belongs to the planet of its first hour, and runs from sunrise to the next sunrise rather than from midnight. The instrument names the day in force at the place and moment you choose, draws the week the seven rulers make, and sets out each ruler's correspondences by where they come from.
Preparing the instrument for your time and place
The tradition
The seven-day week of planetary days is Hellenistic. By the first century it was in use across the Roman world, each day named for the planet held to govern it, and the names survive in the Romance languages and, through Germanic gods taken as the planets' equals, in English.
Its order comes from the planetary hours. The hours pass through the seven in the Chaldean order, slowest sphere to swiftest, and twenty-four of them carry the count three places round, so each day opens under the planet three spheres on from the last. Cassius Dio records this explanation in the third century.
Reading the instrument
- The planetary day runs from sunrise to sunrise, not from midnight. Before sunrise the previous day's ruler is still in force, and the instrument says so.
- The dial sets the seven round a circle in the Chaldean order; the heptagram drawn through them in steps of three is the order of the week. The ring round it is the day's light and night on the clock at the place.
- The correspondences are kept apart by kind: those with a named source, those of modern tables, and the site's own gloss.
Where it descends from
- Cassius Dio, Roman History 37.18–19
- The ancient account of why the days follow one another in this order, from the hours and from the musical fourth.
- Agrippa, Three Books of Occult Philosophy II.22 and II.34
- The planets' intelligences and spirits beside their magic squares, and the ground of the planetary hours.
What this does not claim
Sunrise is computed for the Sun's centre at −0.833° at sea level, to within seconds below 65° of latitude. Where the Sun does not rise or set there is no planetary day, and the instrument says so rather than inventing a sunrise. The correspondences are for study and claim no effect.
Continue
Read the subject