Astrology, type of divination that involves the forecasting of earthly and human events through the observation and interpretation of the fixed stars, the Sun, the Moon, and the planets. Devotees believe that an understanding of the influence of the planets and stars on earthly affairs allows them to both predict and affect the destinies of individuals, groups, and nations. Though often regarded as a science throughout its history, astrology is widely considered today to be diametrically opposed to the findings and theories of modern Western science.

Nature and significance

Astrology is a method of predicting mundane events based upon the assumption that the celestial bodies—particularly the planets and the stars considered in their arbitrary combinations or configurations (called constellations)—in some way either determine or indicate changes in the sublunar world. The theoretical basis for this assumption lies historically in Hellenistic philosophy and radically distinguishes astrology from the celestial omina (“omens”) that were first categorized and cataloged in ancient Mesopotamia. Originally, astrologers presupposed a geocentric universe in which the “planets” (including the Sun and Moon) revolve in orbits whose centres are at or near the centre of the Earth and in which the stars are fixed upon a sphere with a finite radius whose centre is also the centre of the Earth. Later the principles of Aristotelian physics were adopted, according to which there is an absolute division between the eternal, circular motions of the heavenly element and the limited, linear motions of the four sublunar elements: fire, air, water, earth.

Special relations were believed to exist between particular celestial bodies and their varied motions, configurations with each other, and the processes of generation and decay apparent in the world of fire, air, water, and earth. These relations were sometimes regarded as so complex that no human mind could completely grasp them; thus, the astrologer might be readily excused for any errors. A similar set of special relations was also assumed by those whose physics was more akin to that of the Greek philosopher Plato. For the Platonic astrologers, the element of fire was believed to extend throughout the celestial spheres, and they were more likely than the Aristotelians to believe in the possibility of divine intervention in the natural processes through celestial influences upon the Earth, since they believed in the deity’s creation of the celestial bodies themselves.

The role of the divine in astrological theory varies considerably. In its most rigorous aspect, astrology postulates a totally mechanistic universe, denying to the deity the possibility of intervention and to man that of free will; as such, it was vigorously attacked by orthodox Christianity and Islam. For some, however, astrology is not an exact science like astronomy but merely indicates trends and directions that can be altered either by divine or by human will. In the interpretation of Bardesanes, a Syrian Christian scholar (154–c. 222)—who has often been identified as a Gnostic (a believer in esoteric salvatory knowledge and the view that matter is evil and spirit good)—the motions of the stars govern only the elemental world, leaving the soul free to choose between the good and the evil. Man’s ultimate goal is to attain emancipation from an astrologically dominated material world. Some astrologers, such as the Harranians (from the ancient Mesopotamian city of Harran) and the Hindus, regard the planets themselves as potent deities whose decrees can be changed through supplication and liturgy or through theurgy, the science of persuading the gods or other supernatural powers. In still other interpretations—e.g., that of the Christian Priscillianists (followers of Priscillian, a Spanish ascetic of the 4th century who apparently held dualistic views)—the stars merely make manifest the will of God to those trained in astrological symbolism.Britannica QuizZodiac Sign Quiz

Significance of astral omens

The view that the stars make manifest the divine will is closest to the concept that lies behind the ancient Mesopotamian collections of celestial omens. Their primary purpose was to inform the royal court of impending disaster or success. These might take the forms of meteorological or epidemic phenomena affecting entire human, animal, or plant populations. Frequently, however, they involved the military affairs of the state or the personal lives of the ruler and his family. Since the celestial omina were regarded not as deterministic but rather as indicative—as a kind of symbolic language in which the gods communicated with men about the future and as only a part of a vast array of ominous events—it was believed that their unpleasant forebodings might be mitigated or nullified by ritual means or by contrary omens. The bāru (the official prognosticator), who observed and interpreted the celestial omina, was thus in a position to advise his royal employer on the means of avoiding misfortunes; the omens provided a basis for intelligent action rather than an indication of an inexorable fate.

Purposes of astrology

The original purpose of astrology, on the other hand, was to inform the individual of the course of his life on the basis of the positions of the planets and of the zodiacal signs (the 12 astrological constellations) at the moment of his birth or conception. From this science, called genethlialogy (casting nativities), were developed the fundamental techniques of astrology. The main subdivisions of astrology that developed after genethlialogy are general, catarchic, and interrogatory.

General astrology studies the relationship of the significant celestial moments (e.g., the times of vernal equinoxes, eclipses, or planetary conjunctions) to social groups, nations, or all of humanity. It answers, by astrological means, questions formerly posed in Mesopotamia to the bāru.

Catarchic (pertaining to beginnings or sources) astrology determines whether or not a chosen moment is astrologically conducive to the success of a course of action begun in it. Basically in conflict with a rigorous interpretation of genethlialogy, it allows the individual (or corporate body) to act at astrologically favourable times and, thereby, to escape any failures predictable from his (or its) nativity.

Interrogatory astrology provides answers to a client’s queries based on the situation of the heavens at the moment of his posing the questions. This astrological consulting service is even more remote from determinism than is catarchic astrology; it is thereby closer to divination by omens and insists upon the ritual purification and preparation of the astrologer.

Other forms of astrology, such as iatromathematics (application of astrology to medicine) and military astrology, are variants on one or another of the above.