Ptolemy (c. 150 AD), whom many consider to be the greatest scientist of the ancient world, authored a major astrological work, the Tetrabiblos(four books on astrology). In it he divided astrology into two fundamental categories: Universal and Genethlialogical. The former was concerned with natural phenomena such as climate, weather, tides, agriculture, plagues, etc. The later was concerned with the affairs of humans. (This division can also be observed in Indian, Chinese and Mesoamerican astrology). By the Renaissance these two branches had come to be known as natural and judicial astrology. On the verge of the scientific revolution there was no quarrel over natural astrology, but judicial astrology was under heavy attack from religion and those humanists who believed Man to be completely separate from nature.
Rheticus, Cardano, Dee, Brahe, Kepler, Bacon, Galileo and many other notables in the history of science either practiced natural astrology or supported it in principle. Kepler, in particular, was interested in this subject, published on it, and developed a scientific methodology to investigate weather from an astrological perspective. Kepler’s method was expanded upon during the mid 17th century by John Goad, an amateur scientist who authored a major work, the Astro-Meteorologica. It has been argued that the much of science during the 17th and 18th centuries contained (or inherited) elements of the natural astrology tradition, particularly in regard to natural philosophy and methodology.
The decline of natural astrology is a complex topic that requires an analysis of both philosophical and political changes during the later part of the 17th century and all of the 18th. There was never a clean break and modern historians of science appear to have offered a strongly biased interpretation. Scientific meteorology involved astrological indicators up to the late 18th century. From the early 19th century to the present day, astrological weather forecasting continued to exist as a tradition in annual almanacs. A few English and American astrologers in the 19th century wrote on natural astrology, but more as a review of established methodology and less as an ongoing investigation. Natural astrology was now more often referred to as mundane astrology, which included both historical and climatological cycles as well as astrometeorology.
During the early decades of the 20th century a number of influential historians of science declared astrology to be completely dead and an embarrassment to the history of science. However, throughout the 20th century a number of astrologically-minded researchers did investigate possible correlations between natural phenomenon and solar/planetary cycles and positioning. Some of these have used a time-slice methodology, i.e. a horoscope calculated for a specific astronomical moments thought to offer insights into the larger processes operating on the Earth. Others focused solely on the angular separations of the planets (aspects) and some utilized a heliocentric perspective.
In the 1930’s electrical engineer and astrologer Edward Johndro proposed a mechanism for astrology involving the Earth’s magnetic field. John Nelson, who for many years lectured at astrology conferences, developed in the 1940’s and 50’s a very successful methodology for predicting solar storms (for RCA) using elements of classical astrological methodology. In the 1960’s astrologer Donald Bradley found a lunar-cycle/rainfall correlation that was in line with John Goad’s observations 300 years earlier (it was published in Science). From the 1960’s to the early 21st century, German scientist Theodore Landscheit correlated climate patterns with the movement of the solar system’s barycenter, which itself is modulated by planetary cycles. He viewed the sun and planets together as an intricate “organism” regulated by complex feedback loops. The sun, making the planets revolve around itself, is in turn influenced by the planets which make it revolve around the center of mass of the entire system. These complex movements produce solar activity which, in turn influences the Earth’s atmosphere via the solar wind. Landscheit’s work is closely related to that of scientists Rhodes Fairbridge and John Sanders who have also stressed the importance of planetary patterns in determining the sun’s motion with respect to the barycenter and the corresponding “effects” on the Earth. More recently, English astronomer Percy Seymour has argued that planetary alignments may directly affect the Earth’s magnetic field. In this regard he has suggested that very small gravitational forces can produce very large effects on magnetic fields and has proposed a formal theory of magneto-tidal resonance with mathematical modeling.
Biology was a part of the tradition of natural astrology as it pertained to plagues, agriculture, and also to the lunar cycles apparent in marine life. It is well-known that organisms respond in many ways to daily (circadian) cycles and also to various lunar rhythms. Changes in light and possibly sensitivity to lunar gravitation are considered reinforcing or even driving forces in such cycles. Sensitivity to the Earth’s magnetic field is also apparent in some organisms (eg. magnetotactic bacteria, animal navigation, etc.). There is also evidence of longer cycles in organisms, (i.e. abundance, reproduction, etc.), that have not been adequately explained. What is not generally not considered as possible markers of biological time, are cycles involving astronomical bodies other than the sun or moon.
It is possible that other bodies in the solar system, especially Venus, may play a role in the life cycles of some organisms. Spikes in the geo-magnetic index may be registered by organisms just as contrasts in visible light are used for navigation in the environment. It is also possible that certain organisms may be responding collectively to planetary cycles on a scale that is evident only over the course of several generations. The database established by the Foundation for the Study of Cycles at the University of Pittsburgh points to the existence of a great many 8-year and 9.6-year cycles (of mammals, birds, insects, etc.). The synodic cycle of Venus (Sun-Venus) is 584 days on average. Five cycles is equal to 8 years exactly, 6 cycles equal 9.6 years. Exactly what is driving these cycles is not known, and if they are linked to the synodic cycle of Venus, could be the focus of an investigation. Mesoamerican astrology was founded, more or less, on the cycles of Venus and surviving records point to correlations with climate and agriculture.
While a number of mechanisms have been proposed to explain how planetary bodies may influence the Earth and its organisms, possibly the most plausible at the present time has to do with responses to subtle fluctuations of the Earth’s magnetic field generated by the sun’s output, which in turn is modulated by planetary positions. The cycles of Jupiter and Saturn together appear to have a powerful affect on the solar cycle itself, which, in turn, then influences the Earth’s magnetic field. A possible study would involve an investigation into measurable fluctuations of the various magnetic indices and possible correlations with planetary alignments, followed by a search for further correlations with the upper atmosphere, weather patterns, and organic systems.