Introduction to Astronomy

He renewed it: and for future generations, he prepared a path of proven methods to follow thereafter. Thus, if Ptolemy Claudius Ptolemy, the 2nd-century Greco-Egyptian astronomer or any other observer, having recorded a star in a fixed position—noting its place on the circle of retrogradation The apparent backward motion of a planet in the sky and its place on the eccentric circle—were to simply leave it and wait until it returned to those exact same positions on both circles simultaneously while attempting to restore the study, nothing would ever have been perfected. Nor would the various circles of the stars, the differences in their orbits, the apsides The points in an orbit closest or furthest from the center, the digressions, the retrogradations, and things of that kind ever have been understood.

In this same manner, in our own era, by observing the positions of the stars through the signs of the Zodiac and the nature of their influences, we have arrived at a complete science through a reasonable and continuous order. For when the age that followed brought the experiments of our predecessors down to the memory of posterity through writing, it also tested the powers of the stars in its own time. Thus, adding to the paternal discoveries and leaving their own findings to the next generation, they left whatever was lacking to be easily completed, the way having been prepared.

¶ The sixth sect is led astray into error by their own mistake regarding astrology. For there are men devoted to the calculation of the stars who, while deviating from the path of the book Almagest Ptolemy's definitive 2nd-century mathematical and astronomical treatise—in which the entire truth of universal wisdom is contained—find different positions for the stars based on specific placements taken from other sources. By their own error, they introduce a double blasphemy against astrology.

First, they claim that the true locations of the stars can rarely be found. They argue that because the data they use—whether in the mean motions of the stars or the precision of the following second and third minutes Refers to sexagesimal fractions of a degree: minutes, seconds, and thirds—increases or decreases over a long period of time, it either leaves the positions of the stars behind or pushes them forward by a significant amount.

Second, they claim that the truth of an astrological judgment cannot be attained except by the absolute precision of the points of the stars. These men attribute the error of their own judgment to an innocent art. We answer them with a two-fold reason:

1. In the first place, the astrologer judges the general occurrences of things from the properties of the stars, the natures of the signs, and the conditions of the houses. While individual degrees relate more to the specific conditions of individual things, an error of a few points or even entire degrees does not greatly hinder the general judgment.
2. Secondly, in judgments, it follows that because this or that star is in this or that place of the circle or sign, this or that will happen regarding the accidents of things. However, it is the duty of the calculator compotiste A person who calculates astronomical tables or the calendar to derive that location with certain truth.

Therefore, when an astrologer follows the influences of the stars according to the nature of their locations in judging events, if he is sometimes deceived, it is seen as the fault of the astronomer The one calculating the positions, not the astrologer. This undoubtedly happens because some men of that study, having abandoned the truth of general wisdom, turn to particulars and are content with any calculation based on a weak root The "root" or radix is the starting numerical value used for astronomical calculations. Consequently, over a long time, a great cost of error necessarily grows. Thus, the placement of the stars—whether taken through fixed locations of the signs, or determined by the conjunctions of certain stars with reliable instruments, or even by sight—is found to be otherwise.

¶ For this reason, we enjoin the astrologers themselves to abandon the wandering and uncertain authority of particular calculations and most studiously follow the locations of both the wandering planets and fixed stars according to the truth of complete wisdom, which the Almagest confirms with certain dimensions and ingenious instruments.

¶ The seventh sect [of] science...