Among the oldest and most practical tools of traditional astrology are the planetary hours. This is a system that assigns each hour of the day and night to one of the seven classical planets, creating a continuous rhythm that ties everyday time to the sky. Planetary hours appear in manuals of electional astrology, in texts of astral magic such as the Picatrix and in many Renaissance collections of correspondences. They are also the origin of the names of the days of the week.
Unequal hours, not clock hours
The first thing to understand is that a planetary hour does not last sixty minutes. Tradition uses so-called unequal or temporal hours: the period of daylight between sunrise and sunset is divided into twelve equal parts, and the same is done with the period of darkness between sunset and the following sunrise.
As a result, in summer the daytime hours are long and the night hours short, while in winter the opposite happens. Only at the equinoxes do day and night hours last roughly the same. This system was normal in the ancient world: liturgical hours and Roman sundials also followed the light, not an abstract time.
The Chaldean order as the engine of the system
The hours follow one another according to the Chaldean order of the planets, from slowest to fastest:
- Saturn
- Jupiter
- Mars
- Sun
- Venus
- Mercury
- Moon
After the Moon, the sequence starts again from Saturn. The first hour after sunrise is always ruled by the planet that gives the day its name: the Sun on Sunday, the Moon on Monday, Mars on Tuesday and so on. From there the sequence runs without interruption, hour after hour, through the day and the night.
A concrete example
Take a Sunday. The first hour of the day belongs to the Sun, the second to Venus, the third to Mercury, the fourth to the Moon, the fifth to Saturn, the sixth to Jupiter, the seventh to Mars, the eighth to the Sun again. Continuing, the first hour of the night, the thirteenth of the cycle, falls to Jupiter. When you reach the twenty-fifth hour, the next sunrise, the sequence lands on the Moon: and so the following day is Monday. This is no coincidence; it is the mechanism that produced the planetary week.
How to calculate them in practice
To calculate the planetary hours for a place you only need the times of sunrise and sunset for that day and location.
- Work out the length of the day, from sunrise to sunset.
- Divide it by twelve: this gives the length of one daytime hour.
- Work out the length of the night, from sunset to the next sunrise.
- Divide it by twelve: this gives the length of one night hour.
- Give the first hour to the planet of the day and continue in Chaldean order.
Suppose sunrise is at 6:00 and sunset at 20:00. The day lasts fourteen hours, or 840 minutes, so each daytime hour lasts 70 minutes. The night lasts ten hours, or 600 minutes, so each night hour lasts 50 minutes. On a Tuesday, the first hour (6:00-7:10) belongs to Mars, the second (7:10-8:20) to the Sun, the third (8:20-9:30) to Venus, and so on.
Because sunrise and sunset change with latitude, the planetary hours of Palermo do not match those of Milan on the same day. That is why it matters to use the data for the place where you are.
What planetary hours were used for
In tradition, planetary hours were a way of tuning an action to the quality of the moment. The most common associations are these:
- Saturn: long tasks, tidying up, deep study, bringing matters to a close.
- Jupiter: requests, agreements, legal and religious matters, generosity.
- Mars: physical activity, clear-cut decisions, work that demands courage.
- Sun: meetings with authority, matters of prestige and visibility.
- Venus: relationships, art, beauty, reconciliation.
- Mercury: writing, study, trade, communication, contracts.
- Moon: travel, household matters, anything to do with nourishment and change.
In texts of astral magic the hours were used to choose the moment for preparing a talisman or reciting a prayer dedicated to a planet. At Studio Esoterico Cornelio planetary hours are offered above all as a practice of awareness: a way of living time qualitatively and not only quantitatively.
Limits and common sense
Planetary hours are a refinement, not a rigid rule. Tradition itself considered them less important than the real position of the planets in the sky and the condition of the Moon. Using them with balance means not giving up a necessary commitment just because it falls in the "wrong" hour, but choosing, when possible, a moment consistent with your intention.
In short
- Planetary hours divide day and night into twelve parts each, with lengths that change with the seasons.
- The first hour after sunrise belongs to the planet of the day; the following ones follow the Chaldean order.
- To calculate them you only need the local sunrise and sunset times.
- Each planet is associated with a kind of activity, according to electional and magical tradition.
- They are a symbolic tool for living time attentively, not a guarantee of outcome.