You might ask why calculating Primary Directions by hand is necessary in the computer age. The answer is quite simple. First there is no software on the market that is affordable, easy to use and where primary directions as understood by the older astrological writers (Wm. Lilly, J.B- Morin, Joh. Schöner, Junctinius, etc.) are presented. Secondly it helps when their calculation is a little transparent and when that ideal Primary Direction programme comes along what convenience it represents!
As it is not easy to find a step-by-step calculation guide for directions I am presenting one here. This is for the stout-hearted as the calculations involve 7 steps. But if done systematically, it doesn’t take that long.
They are based on Erich Carl Kühr’s calculation example in his book, “Berechnung der Ereigniszeiten”. Erich Carl Kühr (1899-1951), is a fairly unknown German astrologer. One of his great merits, are his tables for both Right Ascension and Oblique Ascension. He was a proponent for the use of Primary Directions, and did his best to make their calculation and use as simple as possible. You will need two sets of logarithmic tables if you want to do these calculations. The first is a table of goniometric, trigonometric logarithms. The second is a table of Proportional Logarithms for 0 to 179 degrees. I have tried to find them in the internet but was not very successful. Should a reader find them I would greatly appreciate a link in the comments section to this post! (thank you in advance)
The ‘ingredients’ needed for the calculations are quite interesting:
- longitude, latitude and declination of the planets
- latitude of the birthplace
and the process:
Consider the trigonometry as a means of finding an unknown quantity (the right-ascensional arc or the oblique ascension) with known factors (longitude, latitude and declination of a planet, latitude of birthplace). It is not unlike calculating the base of a triangle given the length of the hypotenuse and the height of the side that is ‘elevated’. The trigonometric functions are merely proportional relationships to help accomplish what would otherwise be a staggering task.