Planetary Hours (行星時)

The Chaldean Clock — the Hours That Named the Week

Overview

Before the mechanical clock, the West kept a different kind of time: the day from sunrise to sunset divided into twelve hours, the night from sunset to the next sunrise into twelve more — hours that stretch in summer and shrink in winter — each one ruled by a planet. The rulers cycle endlessly through the Chaldean order, slowest to fastest: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. And here is the astonishing part, recorded by the Roman historian Cassius Dio: because twenty-four leaves a remainder of three against seven, stepping a full day through the cycle lands on the next planet in a new sequence — Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn. That sequence is the week. Sunday, Monday, Saturday — the names your calendar wears are the fossil of this system. askTIAN computes the full unequal-hour table for any date and place on Earth, marks the current hour, and serves the classical electional layer — which hours the tradition holds good for love, trade, courage, or endings — exactly as Agrippa and the Key of Solomon give it.

Origin & history

The planetary hours descend from Hellenistic astrology's merger of the Egyptian 24-hour day with the Chaldean planetary order — the seven classical planets ranked by apparent speed, Saturn slowest and outermost, the Moon swiftest and nearest. Assigning each hour a ruler in that order, and naming each day for its first hour's ruler, produced the planetary week that spread through the Roman Empire and never left. Cassius Dio, writing in the third century, explains the mechanism explicitly — and askTIAN turns his explanation into an assertion: at every engine load, the code re-derives the week from pure hour-stepping, and refuses to serve if the theorem fails. The system's electional use — choosing the hour whose ruler favors your undertaking — runs through the grimoire tradition: Agrippa's De Occulta Philosophia catalogues the hours' virtues, and the Key of Solomon opens with them as the first practical instruction of the art.

The unequal hour survived in monastic timekeeping, in the astrolabe's hour-lines, and in every almanac that printed 'the hour of Jupiter' beside sunrise tables. The tradition's mechanics never varied: the first hour of the day belongs to the day's planet, the cycle runs unbroken through both halves, and the night's hours run to the next day's sunrise — which is why day and night hours differ in length everywhere except near the equinoxes, when both approach the familiar sixty minutes. askTIAN's implementation honors every classical convention, including the one modern apps most often fumble: an instant before sunrise belongs to the previous planetary day, not the calendar date on your phone. The electional attributions served with each hour are the tradition's own — from public-domain sources two to five centuries old — and are labelled as the tradition's claims, never as validated advice.

How it works

Give the engine a date, coordinates, and timezone offset. It computes sunrise and sunset with the same gold-tested solar solver behind askTIAN's Vedic panchanga (upper limb, −0.833° with refraction), plus the next day's sunrise for the night hours. The day arc is divided into twelve, the night arc into twelve, and rulers are assigned by stepping through the Chaldean order from the weekday's lord — Sunday's first hour is the Sun's, Monday's the Moon's, and so on, exactly as the week's names promise. Each of the twenty-four hours returns its start and end to the minute, its length (day and night hours differ — that is the point of unequal hours), its ruler with symbol, and the classical goodFor/avoidFor elections. Pass an optional HH:MM and the engine marks your current hour — or tells you, correctly, that a 3 a.m. query belongs to yesterday's planetary night. The structure is verified three ways: the weekday-generation theorem is asserted at every load, equinox and solstice hour-length properties are locked as tests, and the daytime ruler is cross-checked against the independent hora indexing of the panchanga engine. Polar latitudes are refused rather than fabricated: no sunrise, no hours.

Good for

Use cases

The Hour Ribbon

A single call renders the day as a ribbon of twenty-four colored hours — rulers, symbols, exact boundaries — with 'now' marked. The oldest dashboard widget in the world, computed fresh for the user's coordinates.

The Electional Planner

Surface the day's hours of Jupiter and Venus as suggested windows for asks and meetings, with the tradition's goodFor lists as copy — labelled as tradition, timed by real astronomy.

The Timing Stack

Combine with moon.voidOfCourse and retrograde.track: is the Moon void, is Mercury retrograde, and whose hour is it? Three calls, one complete classical timing verdict.

The Week Explainer

An evergreen content piece straight from the response's weekTheorem field: why Saturday follows Friday — the 24 ≡ 3 (mod 7) arithmetic that named the days, demonstrated live.

Key terms

Chaldean Order
The seven classical planets ranked by apparent speed, slowest first: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon. The hour rulers cycle through it endlessly.
Unequal Hours
Day (sunrise→sunset) and night (sunset→next sunrise) each divided into twelve — so a summer day-hour may run 75 minutes while its night-hour runs 45. Only near the equinoxes do both approach 60.
Day Lord
The planet ruling a day's first hour — and naming the day: Sunday the Sun's, Monday the Moon's, through Saturday, Saturn's.
The Week Theorem
24 ≡ 3 (mod 7): stepping a full day through the Chaldean cycle lands on the next day's lord, generating the week's order — the recorded origin of the weekday names, asserted at every engine load.
The Pre-Sunrise Convention
An instant before sunrise belongs to the PREVIOUS planetary day — 3 a.m. Saturday is still Friday's night, and the engine says so instead of silently misfiling it.
Elections
The tradition's hour-by-ruler recommendations — Venus for love, Mercury for contracts, Saturn for endings — from Agrippa and the Key of Solomon, served as the tradition's claims, never as validated advice.
Planetary Day
Sunrise to next sunrise — the unit the 24 hours divide. The calendar date is only a label; the astronomy draws the real boundaries.
Polar Refusal
Above ~66° latitude the sun may not rise or set at all; the engine refuses those queries rather than fabricating hours that cannot exist.

API

The askTIAN Planetary Hours API computes the full classical unequal-hour table for any date and coordinates — twelve day hours and twelve night hours to the minute from the shared gold-tested solar solver, rulers stepped through the Chaldean order from the weekday lord, the current hour marked with the pre-sunrise convention honored, and each hour's electional layer served from public-domain classical sources as the tradition's claims. The weekday-generation theorem (24 ≡ 3 mod 7 — the arithmetic that named the week, per Cassius Dio) is asserted at every engine load, equinox and solstice hour-length properties are locked as tests, and the daytime ruler is cross-checked against the independent Vedic hora engine. Polar latitudes refused. Pure compute, no LLM, 2 TIAN.

Endpoint: POST /trpc/planetaryHours.day — 2 TIAN Points. See the API documentation and Playground.