Resources / Celestial timing
Zodiacal Hour Calculator
Sunrise to the next sunrise in twelve equal periods, led by the sign the Sun stands in at sunrise, with the signs as they actually rise over the place drawn beside them.
Preparing the instrument for your time and place
The tradition
Before clocks imposed equal hours, the day was divided by light. Sunrise to sunset made twelve hours and sunset to sunrise made twelve more, so an hour stretched and contracted with the season — long summer days, short summer nights.
The zodiacal division applies the same instinct to the signs rather than the planets: the daily circuit is cut into twelve zodiacal periods, so each stretch of the day carries a sign's character. It is a way of reading the day as a compressed year.
Reading the instrument
- The instrument divides sunrise to the following sunrise into twelve equal periods, beginning from the Sun's sign at that sunrise.
- Because the periods are keyed to actual sunrise, their length shifts with latitude and season — this is a feature of the system, not drift.
- Compare against planetary hours: the two schemes divide the same day differently and are often used together rather than as alternatives.
- The inner ring of the dial shows the signs as they actually rise over the place. They take unequal times, under an hour for some and three for others, so the equal periods are a convention set beside the sky, not a picture of it.
Where it descends from
- The unequal-hour tradition
- The seasonal-hour reckoning shared by Greek, Roman, and medieval timekeeping, from which planetary and zodiacal hour schemes both descend.
- Picatrix and Agrippa
- The magical literature in which hour divisions are put to electional use.
- Ptolemy, Almagest, book II
- Tables of the signs' rising times by latitude, the ascensions; the instrument computes them instead from the ascendant.
What this does not claim
Sunrise and sunset are computed for the Sun's centre at −0.833° at sea level, to within a few seconds below 65° latitude. Where the Sun does not rise or set, the instrument says so. The rising signs are not shown beyond 66° of latitude, where some degrees of the zodiac never rise.
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