Planetary hours are the oldest working timing system in Western magick, they are genuinely elegant, and about half the tables and apps in circulation calculate them incorrectly. The error is always the same one, so let us deal with it first.

The mistake

A planetary hour is not sixty minutes long.

The day is divided into twelve hours of daylight and twelve hours of night, where daylight runs from sunrise to sunset and night runs from sunset to the next sunrise. Those two periods are then each divided into twelve.

Which means the length of an hour changes with the season and with your latitude.

In Scotland this is not a technicality, it is the whole thing. In midsummer at the latitude of Inverness you might have around eighteen hours of daylight, giving day hours of roughly ninety minutes and night hours of about thirty. In midwinter it inverts. At the solstices the difference between a day hour and a night hour is enormous.

Anyone handing you a fixed table that says the hour of Mars runs from 09:00 to 10:00 has not understood the system. Any calculation that does not ask for your location and your date is wrong.

These are called unequal hours, or temporal or planetary hours, and they were the standard way of reckoning time in the classical and medieval world for everybody, not just magicians. The equal hour is the innovation, and it arrived with mechanical clocks.

The order

The planets run in a fixed sequence, the Chaldean order, arranged from slowest apparent motion to fastest:

Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon.

That is the whole cycle. When you reach the Moon you go back to Saturn and continue. It never varies and it never resets at sunset; it runs continuously through day and night.

How the days get their rulers

This is my favourite piece of the whole system, because it explains something you have known your entire life without knowing why.

The first hour of each day, beginning at sunrise, is ruled by that day's planet. Then you count through the Chaldean order.

Twenty-four hours later you have gone round the seven-planet cycle three times with three left over, which lands you three places along. Do that repeatedly and you generate this sequence:

Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn.

Which is: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday.

The names survive intact in the Romance languages and in English through the Norse substitutions. Mardi is Mars. Tuesday is Týr. Mercredi is Mercury. Wednesday is Woden. Jeudi is Jupiter. Thursday is Thor. Vendredi is Venus. Friday is Frigg.

The order of our week is a direct fossil of the planetary hour calculation. That is not a magickal claim, it is documented history, and it is one of the genuinely astonishing pieces of continuity in ordinary life.

Calculating it

  • One. Find sunrise and sunset for your exact location and date. Not a national average.
  • Two. Daylight length divided by twelve gives your day hour. Night length divided by twelve gives your night hour.
  • Three. The first day hour begins at sunrise and is ruled by the planet of the day.
  • Four. Count forward through Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, repeating.
  • Five. At sunset switch to night hour length and keep counting without resetting.

A worked example. Sunrise at 08:00, sunset at 16:00, on a Friday in a Scottish December.

Daylight is eight hours, so a day hour is forty minutes. Night is sixteen hours, so a night hour is eighty minutes.

Friday's first hour, from 08:00, is Venus. Then Mercury at 08:40, Moon at 09:20, Saturn at 10:00, Jupiter at 10:40, Mars at 11:20, Sun at 12:00, and so on. At 16:00 the first night hour begins, and it is eighty minutes long.

Do it by hand once. It takes ten minutes and it will make every table you ever look at afterwards intelligible.

What each hour is for

The traditional attributions, kept brief because they are also in your Planetary and Celestial Correspondences database.

  • Saturn. Endings, boundaries, binding, banishing, structure, discipline, land, the dead, patience, long work.
  • Jupiter. Expansion, abundance, authority, law, generosity, opportunity.
  • Mars. Conflict, courage, cutting, protection through force, energy, surgery, decisiveness.
  • Sun. Success, health, authority, visibility, illumination, leadership.
  • Venus. Love, beauty, friendship, art, reconciliation, pleasure, harmony.
  • Mercury. Communication, travel, learning, negotiation, writing, commerce, trickery.
  • Moon. Dreams, intuition, the tides, the domestic, the hidden, psychic work, water.

Where the honesty is required

Two things worth saying, in keeping with the rest of this site.

This is a Hellenistic and Arabic inheritance, not a Celtic one. Planetary hours come to us through Greek astrology, through the Islamic astrological tradition, through medieval Latin grimoires and the Renaissance magi. Agrippa's Three Books of Occult Philosophy in 1533 is the standard route into English practice.

There is nothing Gaelic about it. There is no evidence anybody in the Highlands was timing a working by the hour of Mercury. Gaelic timing tradition works on entirely different principles: the quarter days, the two halves of the year, sunwise and widdershins, the threshold hours of dawn and dusk, the turn of the tide, the state of the moon.

I use both, and I do not pretend they are the same inheritance.

And the older sources disagree with each other. Different grimoires assign different operations to different hours, and the attributions above are a consensus rather than a canon. Treat them as a working convention.

Is it worth it

I think so, for two reasons that have nothing to do with whether planets influence anything.

  • It makes you attend to the actual sky. You cannot calculate a planetary hour without knowing when the sun rises and sets where you are standing today. In Scotland that is a dramatic, mood-altering piece of information that most people now ignore entirely. The system forces you outside and forces you to notice.
  • It imposes a wait. If the right hour is at four tomorrow morning, you do not do the working now. That gap between deciding and acting is where a surprising number of bad workings quietly die, and I would not want to lose it.

Practical use

  • Do not over-engineer. Day ruler plus moon phase covers most needs. Reach for the hour when something is important or delicate.
  • Combine day and hour. The hour of Venus on a Friday is Venus doubled. That is the strongest simple timing available and it needs no software.
  • Use a proper calculator, or do it by hand. Anything that does not ask your location is wrong. Astro-Seek and Astrolabe both handle unequal hours correctly. Sunrise and sunset for a UK location: Met Office or timeanddate.com.
  • Note the Scottish extremes. In midsummer north of Inverness you will have very few genuinely dark hours and the night hours become absurdly compressed. Above the Arctic Circle the system breaks entirely. That is not a flaw; it is a system built at Mediterranean latitudes running at ours, and it is worth knowing where it strains.

Sources

  • Agrippa, H. C. (1533). Three Books of Occult Philosophy, Book II, on planetary hours and their attributions. Full text at the Internet Sacred Text Archive and in Eric Purdue's 2021 translation, Inner Traditions.
  • The Key of Solomon the King (Clavicula Salomonis), ed. Mathers. Full text, for the operations assigned to each hour.
  • Ptolemy, Tetrabiblos, for the Hellenistic foundation. LacusCurtius.
  • Davies, O. (2009). Grimoires: A History of Magic Books. Oxford University Press. For how this material travelled into vernacular British practice.
  • Planetary hours — Wikipedia, for the Chaldean order and the derivation of the weekday names.
  • Astro-Seek planetary hours calculator — handles unequal hours by location correctly.
  • Met Office — sunrise and sunset for UK locations.
  • Carmichael, A. (1900). Carmina Gadelica. Full text, for the Gaelic timing principles referenced above.

Cross-reference: slynkycat Planetary & Celestial Correspondences database.

Related: [The Quarter Days: Scotland's Actual Calendar]; [How to Read an Esoteric Claim]; [Fixing and Dressing: Candle Work as Activation]