The day is cut in two, then each half into twelve. A planetary hour is therefore nothing like a clock hour: in London in June it runs about eighty-three minutes by day and thirty-seven by night, and in December the other way round. The seven bodies take their turn in the Chaldean order, the order of their apparent slowness, and the wheel starts over as soon as it reaches the end.
The consequence fits in one line, and it is the part that survived everywhere: twenty-four hours later the wheel of seven does not land on the same body but on the third one along. That is where the order of our weekdays comes from, and it has no other. Saturday belongs to Saturn, Sunday to the Sun, Monday to the Moon: nothing in the sky strings those three together, only the table does.
Hours and their lords in Vettius Valens and Paulus Alexandrinus; the weekday derivation in Dio Cassius; taken up again by Al-Biruni, then by Agrippa and the Latin tradition.
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Where the sources do not agree
A planetary hours table found online almost always announces one set of rules and never mentions that others exist. Others do exist. Here they are, what the sources say about them, and what we settle on.
- Unequal hours or sixty-minute hours
- The ancient sources divide the day into twelve and the night into twelve, which gives hours whose length moves with the season. Several modern almanacs and programs instead cut twenty-four sixty-minute hours from sunrise, sometimes even from midnight. The two methods agree only at the equinoxes, and the gap passes twenty minutes per hour at the latitude of London in June.
- We divide into twelve, as Valens, Paulus Alexandrinus and Al-Biruni do. The two lengths printed above the table are there so you can check it at a glance.
- The day starts at sunrise, at midnight or at sunset
- The rotation of the hours starts at sunrise, and on that the sources agree. But the day of the WEEK changes its name at midnight in the civil calendar and at sunset in the Jewish and Islamic ones. Hence a real disagreement: on a Saturday at eleven at night, do the running hours still belong to Saturn's wheel, or already to the Sun's?
- Here the planetary day runs from one sunrise to the next with no break at midnight: the twelve night hours belong to the day whose sunrise opened them. That is Al-Biruni's reading, and the only one that lets the twenty-four steps land correctly.
- Two orders of the spheres, and Ptolemy declines to choose
- The Chaldean order puts the Sun in the middle of the seven, between Mars and Venus. The older order, called Egyptian, puts it just above the Moon, with Venus and Mercury passing above it. Ptolemy reports both in the Almagest and says nothing allows a decision, since those bodies show no observable parallax.
- We use the Chaldean order, for a reason you can check on the table above: it alone, counted twenty-four steps a day, produces the week we actually have. The Egyptian order would make Sunday be followed by a day of Jupiter.
- What counts as sunrise
- Sunrise is sometimes the moment the Sun's upper limb touches the horizon, refraction included, and sometimes the moment its centre crosses it geometrically. A few minutes separate the two conventions, and every one of the twenty-four hours shifts by as much.
- We take the upper limb with mean refraction, that is the Sun's centre fifty arcminutes below the horizon: the almanac convention. It is the same sunrise that dates every solar day on this site, computed from the same sidereal time as the Ascendant, so a sunrise here can never contradict a chart.
- Why the week runs in that order: two explanations
- Dio Cassius, our oldest source on the question, gives two. The first is the count of the hours, the one on the table above. The second counts by fourths along the order of the spheres and reaches the same result by another road. He reports both and picks neither.
- We show the first, because it can be demonstrated row by row on a table. That is no verdict on the second, whose result is identical: what is at stake is the cause, not the sequence of days.
- The angel names attached to the hours
- The Latin tradition, from Agrippa to the Heptameron, gives every hour of day and night an angel's name, different for each day of the week. These lists vary from one manuscript to the next and from one printing to the following, and no version carries authority over the others.
- We serve none of them. A list that changes between copies is not reference data, and giving one without saying which would be choosing in silence.
- Beyond the polar circles
- The sources were written at latitudes where the Sun rises every day. None of them says what to do when it does not rise, or when it stops setting: the question did not come up.
- We cut nothing when there is nothing to cut, and we say which of the two cases we met. Twice a year there is even a day that rises, sets, and whose tomorrow never rises: its night has no observable end, and the table says so instead of closing it on an invented hour.
What we do with it
Nothing in the readings this site sells is dated by the planetary hour. The natal chart is read on the sky of a birth, transits on the sky of the day, the year reading on profections and firdaria. Laying the planetary hour on top would not add a single statement: it would put a second division on a sky that already has one.
This page exists for another reason: the planetary hour is the old technique you meet everywhere, in almanacs, in horary astrology, in the grimoires, and almost never with its source attached. William Lilly, in 1647, uses it to test a horary question: if the lord of the hour and the Ascendant do not agree, he distrusts the question. Knowing where a thing comes from beats copying a table.
One thread does tie this table to the rest of the site. The same wheel of seven, started from a different point, rules the faces of the zodiac ten degrees at a time, beginning with Mars at the first degree of Aries. You will find it column by column in the table of dignities.
Table of essential dignities →
And your own birth sky?
The hours are counted the same way for everyone standing in the same spot. Your chart belongs to your date, your time and your place alone.