The astronomy of primum mobile: Placidean directions under the pole

Since the Antiquity astrology (and prediction) was based on astronomical tables generally divided into three different parts collected together: tables of primum mobile, tables of planetary positions, eclipses; at the beginning of the Renaissance tables of primum mobile were separated from the rest: the most famous of all Regiomontanus’ ones, which the author called “Tables of directions” because they were used in order to calculate directions. (( Johannes Regiomontanus,  Tabulae directionum profectionumque, non tam Astrologiae iudiciariae, quam tabulis instrumentisque innumeris fabricandis utiles ac necessariae, several editions ))

Between the other tables – see Bezza definitive article “Le tavole del primum mobile nel Medioevo” – I should list the ones of Johannes Engels, ((  Johannes Angelus, Astrolabium planum in tabulis ascendens : cotinens qualibet hora atq[ue] minuto equationes domo[rum] celi mora[m] nati in vtero matris cum quoda[m] tractatu natiuitatum vtili ac ornato, necnon horas inequales pro quolibet climate mundi. (Venetijs: Per Iohanne Emericu de Spira, [for Lucantonio Giunta], 1494).  )) with the illustrated chapter about 360 degrees taken from Albumasar and his Medieval Spanish versions   (( Fritz Saxl, La fede negli astri: dall’antichita’ al Rinascimento (cura Salvatore Settis) (Torino: Boringhieri, 1985 ))  about which readers could find several articles in this blog.

But what is exactly primum mobile?

The “first mover” is the most external immaterial  sphere wrapping the other spheres. According Aristotle the last sphere was the eighth  sphere, the one of the fixed stars, but Dante followed Ptolemy, who added a ninth sphere.

In the Middle Ages to the astronomers were known three different motions of the skies: the daily motion, the precession and the trepidation (the oscillation of the tropical points)  so every external sphere had its own motion: to the fixed stars the precession, the oscillation to an intermediate ninth sphere and the daily motion to the primum mobile, which became the tenth and last. It is the sphere which moves  all the others- receiving his motion directly from God-  the Love that moves the Sun and all the other stars. (( Dante, Paradiso, XXXIII, 145 ))

As the primum mobile (and its motion, the daily motion) has the quality of steadiness, the planetary spheres with their motions represent mutability and changeability.

Ptolemaic system
The system of the spheres

Almost no astronomer or astrologer could resist to give his own version of tables of primum mobile.  The same Placido, true to the semiarc method, gave an alternative, approximate method of it based on poles of planets (where the pole is still based on semiarc) which for some reason  became the “Placidean” way to direct,  or Placidean directions under the pole of significator.

Anyway the method – whichever was its history- seems to work.

Let’s try to calculate a direction under the Pole by hand, so we can see the whole process. (( Data are taken from the speculum given by Morinus software, tables of oblique ascension and descension come from Almugea school ))

Our chart example is Robert Kennedy, the famous brother of the American President J.F.Kennedy.

Robert Kennedy birth chart

According Ptolemy, the Sun in the 7th house is the hyleg of the chart, but according several medieval authors – Bonatti for example- Sun in the 7th should be in a masculine sign to be hyleg, which is not the case, while Moon in the 10th can be hyleg if it is in a feminine sign, like in this chart.

Being the Moon in the 10th house – between the MC and ASC,   in the prorogation made into succeeding signs, the places of the malefics, Saturn and Mars, are anæretic, whether meeting the prorogator bodily, or by emission of rays in quartile, from either side, or in opposition: …….And even the mere degree, in signs following, in quartile with the prorogatory place, as also the degree in sextile, if badly afflicted, which is sometimes the case in signs of long ascension, and, still further, the degree in trine, if in signs of short ascension, are all anæretic. (( Ptolemy, Tetrabiblos, III, 11 ))

So let’s give a look to the direction of the Moon to the trine of Saturn.

Moon pole, the significator, is 7.16.55, her oblique ascension in the hourly circle 303.20.00; Saturn is at 18.18.54 Scorpio, so the trine of Saturn, the promissor,  is at 18.18.54 Pisces.

In Oblique Ascensions table (Saturn’s trine is in the eastern hemisphere) under the Pole 7 let’s check which is the corresponding oblique ascension.


Trine of Saturn OA 349.50
Moon OA 303.20
direction 46.30

Now let’s convert the direction in time using Placido’s key, which is explained like that by his author:

About the measure of directions, authors give different opinions. Some of them understand whole equatorial degrees as whole years; others as the solar motion of the birth day, others, as the mean motion of the Sun, and others in more different methods.

We, with reference to the first year after the birth, the equatorial part on which the Sun goes through in the right sphere  with the motion of the first day after the birth, the one of the second year with the part of the second day, the one of the third with the one of the third day, and so on. We want in fact that the motion would be subsequent, and towards the following places, and moreover that the motion of the Sun from every single day is considered as cause and rule to every year as its effects in order and number.

Let’s see in  practice:

Right Ascension of the Sun at the birth 235.44
Arc of direction 46.30
RA of the Sun 282.14

The RA of the Sun will be equal to 282.14 in the first hours  (around 4:30 AM) of 2nd January 1926, after 42 days and 14 hours corresponding to 42 years and 7 months. which correspond to 20th June 1968.

I got the same result with Morinus software, settings:

Settings for Placdo under the pole directions
Settings for Placido under the pole directions

Note please that:

– I  chose latitude of significator (I’m following here CieloeTerra method); (( See bibliography ))

– Placido’s key is listed in Morinus as “True solar equatorial arc.”

The result from Morinus is the same as the one calculated by hand:

Robert Kennedy was killed on the 6th June 1968 while was running for Democratic primaries. He told:

“There are those who look at things the way they are, and ask why… I dream of things that never were and ask why not.”

Written by Margherita Fiorello, CIDA certified member @ year 2009



Morinus can be downloaded at

Giuseppe Bezza, Le tavole del Primum Mobile nel Medioevo,  in Astronomical amusements (Mimesis Edizioni, 2000). 

Giuseppe Bezza, Marco Fumagalli,  Henry Paul, l’autista di lady Diana , Linguaggio Astrale n. 110, 1998

Martin Gansten , Primary directions: astrology’s old master Technique (The Wessex Astrologer, 2009).

Giancarlo Ufficiale, Le direzioni primarie – students text for  Almugea School

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