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.

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.