Astrology is based on the superstitious belief that the heavens rule our destiny and thus offers people the false consolation that their destinies can be manipulated or altered for personal desire. Many people, up to the present day, still cling to such absurdity that astrology works and newspapers unfortunately do continue to set aside columns for horoscopes which surprisingly retain a large following.
The success of astrology largely relies on loose statements that can be equally applicable to anyone. It has largely been kept alive by the persuasive appeal of confirmation bias, the subconscious ability to cherry-pick supportive evidence while forgetting evidence to the contrary. That one accurate horoscope stands out as a salient confirmation and in turn, induces a self-fulfilling prophecy where people, hence-forth, adjust their personalities accordingly. Their behaviour is ultimately dictated by the prediction.
In reality, astrology does not even have good predictive power. This can perhaps be evidenced by one major study that aimed to examine the validity of astrological predictions over a five year period from 1974 to 1979. The predictive failure rate was 90 percent which means that only 300 predictions were fulfilled.
One way to scientifically test astrological claims is to examine whether the successful predictions are more than one would expect by chance events in the absence of the effect of the astrologer. But, astrologers have so far mostly failed to design experimental studies that run on controlled statistical tests.
Perhaps, one of the most notable studies examining statistical significance of celestial motion and corresponding influences on humans was Michel Gauquelin’s “Mars effect”. The study is most often cited by astrologers as evidence of their claims because it reports that a number of statistically significant sports champions appear to have been born when Mars was directly overhead, between the eastern horizon and the celestial meridian (more than one would expect by pure coincidence alone). Later studies by Gauquelin however were entirely negative and they study was never replicated. It is, therefore, quite possible indeed that Gauquelin’s findings were embellished by selection bias, where the subjects studied are not representative of the target population, for instance because the researcher has only selected subjects who are already athletic and thus their score would be already higher than one would expect by chance.
Aside from the validity of the astrological predictions, the entire concept is nonsensical because it does not take into account the precession of the equinoxes and their motion upon the ecliptic which results in shifts in Earth’s axial rotations and the equinoctial points no longer coinciding with the constellations. Some astrologers counter that by saying that their predictions are actually not based on the pattern of stars but rather on the orientation of the Earth to the sun, the tropical zodiac. This begins with the Sun being at the point where the ecliptic and the equator intersect, known as the vernal equinox. In the tropical zodiac, the vernal equinox is defined as the start of Aries, the first moment of spring and, thus, it would not matter much where the constellations are. The zodiac, in this case, is aligned to the seasons and not the stars. But, even then, this sort of tropical astrology determined with reference to the seasons still would not make sense. That is because any signs that you conceive in the Northern Hemisphere would be reversed in the Southern Hemisphere. A Cancer born in the summers of the Northern Hemisphere would be born in the winters of the Southern Hemisphere. And, a Capricorn born in the winters of the Northern Hemisphere would be born in the summers of the Southern Hemisphere.
There is absolutely no scientific basis for astrology. It is a 4000 year old pseudo-scientific belief masquerading as science that has unfortunately persisted up to the present day.
R.B. Culver and P.A. Ianna The Gemini Syndrome: A Scientific Evaluation of Astrology. Buffalo, NY: Prometheus Books, 1984.
Gauquelin, M. 1972. Planetary effect at the time of birth of successful professionals, an experimental control made by scientists. Journal of Interdisciplinary Cycle Research 3(2): 381-389.
Patrick Grim (Ed.). Philosophy of Science and the Occult. Albany, NY: State University of New York Press, 1982.