Astrology is almost certainly the oldest and most widespread of all pseudosciences. Its origins can be traced back to the first half of the Hammurabi dynasty in Babylonia about 3,500 years ago.
In its modern form astrology asserts that the positions of the solar planets at the time an individual is born are somehow correlated with his or her personality, activities, preferences, and even major life events (accidents, marriages, divorces, etc.). There is no general agreement among astrologers as to how or why this can be. Nor is there agreement as to precisely which planetary positions lead to which specific traits or experiences. It is almost certain that no two astrologers will "cast" an individual's horoscope with precisely the same result. The predictions that do result are often so vague that verification is impossible, anyway.
Astrology is best understood by learning how it began. Like most urban, agricultural peoples, the Babylonians had a pantheon of many gods. They also had a well- developed science of observational astronomy, which served the highly utilitarian purpose of providing a calendar, times to plant and to harvest, times of religious festivals, etc. In this observational scheme each planet was important, and the priests whose task it was to make the observations named the planets for the gods in their pantheon -- Marduk, Isthar, Nergal, etc. By about 1000 B.C. there was an extensive Babylonian literature of "planetary omens." Since Nergal (Mars) was the god of war, a summer in which Nergal shone down brightly from the sky was a good time to wage war (or a time in which risk of war was great). Since Ishtar (Venus) was the goddess of love, a spring night in which Ishtar shone high in the West after sunset was a good time to make love.
About 600 B.C. the Babylonians devised the twelve-sign zodiac: markers in the sky along the path of the sun, moon, and planets, which roughly correspond to the months of the year. The oldest horoscope that has been discovered dates to April 29, 410 B.C. A horoscope is simply a crude chart which indicates the directions in which the various planets lie, relative to the zodiac, at the time of a person's birth. During the classical era dominated by, first, Greece, and then, Rome, Babylonian astrologers (called Chaldeans) set up shop in most large urban areas throughout the civilized world. Greek astronomers scoffed at the Chaldean astrology as absurd, but the Greek public embraced astrology as lovingly as they had embraced many other bizarre or barbaric cults. Later, the Roman statesman Marcus Tullius Cicero wrote, in 44 B.C., a devastating critique of these astrologers, which is still worth reading today. A typical passage: "What utter madness in these astrologers, in considering the effect of the vast, slow movements and change in the heavens, to assume that wind and rain have no effect at birth!"
With the coming of Christianity, the Chaldeans had hard going, since the early Christians (like the Hebrews before them) were hostile to other gods and pagan religions. Of course, there was no way to disguise the essentially religious underpinning of astrology. During the early Middle Ages astrology nearly became extinct in Europe, but was kept alive elsewhere by Islamic scholars.
The Crusades brought astrology back to Europe where it co-existed uneasily with Christianity until the dawn of the age of science. The explosive growth of scientific astronomy from 1600 A.D. paralleled an explosive decline in the fortunes of astrology. By 1900 a French encyclopedia accurately described astrology as a vanishing cult with no young adherents.
Astrology made the strongest comeback in all its history after World War I, when British astrologer R.H. Naylor invented the daily newspaper astrology column.
The paradoxical result is that the heyday of astrology was not during the benighted Middle Ages, when the average person was sunk deep in ignorance and superstition, but rather in the 20th Century, when most citizens presumably know the basic facts of astronomy and are aware that the planets are worlds similar to the earth rather than god-fires in the sky.
Thus, at least 90% of all Americans under age 30 know their sun-sign. There are more than 10,000 practicing astrologers in the U.S., and Americans spend more than $200 million annually consulting astrologers. (In the U.S. there are only about 3,000 professional astronomers, and only about $100 million is spent on basic research in astronomy-- except in space probes.)
Scientists have been quite baffled by the growing popularity of astrology, and a number of them have taken the time to carry out careful studies to see if there is any actual correlation between planetary positions at birth and any attribute of the individual in later life. No statistically valid study has ever shown any connection that would give any validity to any astrological concept-no matter how vaguely that concept has been worded! There is no question about the simple fact that astrology does not work.
Nor is there any reason why it should work. In order to go from an individual's horoscope to a specific prediction of what is in store for that individual, the astrologer must consult a table. This table correlates features of the horoscope (positions of the planets) with individual attributes (intelligence, affection, physical strength, good health, etc.). Where did this table come from? [Note that it is such a table and not the horoscope itself that is the "guts" of astrology.] This table simply is made up by whoever wrote the particular manual of astrology being used. This is why two astrologers can arrive at different (even contradictory) predictions from a single horoscope. There are numerous quite different "astrological systems"; all different, all arbitrary, and all completely disconnected from reality.
This arbitrariness is a characteristic of all pseudosciences, and results because the origins of pseudosciences lie not in observation of nature, but in accidental historical conventions of human culture. For example, the ancients happened to call the second planet from the sun Venus and the fifth planet from the sun Jupiter. If they had done it the other way, it would not have made the slightest difference to astronomy. Venus would then be the big planet with colorful belts and a red spot, while Jupiter would be a hellishly hot planet about the size of the earth. But astrology would then be totally different, because astrology depends entirely on the characteristics associated with the name, not the actual planet! Jupiter, chief of the gods, is a leader of men. Venus, goddess of love, rules the emotions. Changing the arbitrary names would leave reality unaffected but astrology, horoscopes, etc., would become totally different. It is interesting to note that the Maya considered Venus the lord of death.
Another way to see this is to consider the zodiac. The Babylonians, with their interest in the calendar, naturally had 12 zodiacal signs. But again this is arbitrary. Other cultures used 28, for instance the Chinese and Hindus. The Toltec cultures of Middle America used 20. The Babylonians themselves used from 6 to 18 before settling on the "traditional" 12. Again the arbitrary choice of number of signs (not to mention names of signs) is obvious. As for the names, if a given group of stars were called "Aries, the Ram," this arbitrarily chosen name then predetermined the "interpretation" in the tables... for since Rams are aggressive and assertive, so will be people born with the sun (or something) in Aries. How one distinguishes the aggressiveness of the Ram from that of the goat Capricorn or the scorpion Scorpio is another problem! If these groups of stars had been named "The Chair", "The Writing Desk", and "The Castle", interpretations would again be unrecognizably different.
As another example, consider the so- called "house system" of astrology. In order to provide more tables with more characteristics to be looked up, astrological lore has put forward many different (perhaps as many as 50) house systems. These are arbitrary divisions of the sky in sectors, vaguely like orange slices. The various systems differ in how wide these sectors are, how many sectors there are, and how they are oriented in the sky relative to the ecliptic, the horizon or the equator. There are two main house division systems in use by modern astrologers, the Koch and the Placidian. It is hilarious that in neither of these two systems does anyone born above 66.5 degrees north latitude even have a horoscope! The stars have nothing to say about 12 million people!
Another hilarious aspect of astrology is due to the astronomical phenomenon known as the precession of the equinoxes. This was known to Greek astronomers by 150 B.C. and may have been known much earlier. It completely destroys the framework of astrology. The problem is that the early astrologers, for whom the sun rose in Aries at the spring equinox, defined the sign of Aries to be centered on the point of the spring equinox. But as the ancient Greeks knew, the equinox swings in a great circle, taking about 26,000 years to complete its cycle. Thus, today, the sign of Aries is nowhere near the constellation Aries! This detachment of the meaning of the symbol from the random scatter of stars whose arbitrary name originally gave the symbol its name and significance is ludicrous even to many astrologers, who thus disagree with all other astrologers by keeping the sign fixed to the constellation instead of letting it move with the equinoxes!
The moral is that when one has a system based on randomness and arbitrary convention, a shuffle or mixup of the system is undetectable. Astrology is just a random-word generation, and mixing up the procedure by which the random word is generated is not detectable, since the output words remain random with any genuine further mixup. The puzzle is how anyone could not be aware of this randomness, of the mindless conventions that crucially determine the nature of astrology's "predictions".
The question of why people believe in astrology is more interesting than the details of the horoscope. Psychologists have shown that customers are satisfied with astrological predictions as long as the procedures are individualized in some rather vague way. For example, if the astrologer asks for a great deal of personal information before providing the prediction, the individual is much more satisfied with it than if the astrologer asks few questions (and provides the same prediction). The predictions themselves are nearly always very vague and universal in applicability; they might accurately describe nearly anyone.
Astrology relies on an illusion in thinking called personal validation. This depends on the selective nature of memory. If we believe something is so, we tend to remember the events that support it, and for get those which don't. The result is a growing feeling of conviction. We remember the part of the spiel that fits us and forget about the parts which don't. Influencing people this way is called cold reading, and there is a considerable psychological literature on the subject.
Modern science has undercut the basis for astrology at every turn. The individual is formed at conception; not at birth. The gravitational force exerted on a newborn baby by the earth is more than a million times greater than that of any celestial object. The tidal force exerted by the mother and the hospital building is, likewise, a million times greater than that of any celestial body. The electromagnetic radiation falling on the baby from the sun or room lights is a million times more intense than that from any other celestial object. Changes in environment during early development have much greater effects upon the developing person than the events at the time of birth. Also, the time of birth can be altered, to some extent, by the actions of a physician. What are the astrological implications of a caesarean section or forced delivery? Another important point to make is the established role of genes in a person's nature. Suppose two unrelated persons are born at the same time in the same hospital. Will the astrological forces outweigh the genetic ones? The science of genetics has shown the answer to be 'no'. There is nothing whatsoever in all of nature as we have explored it to date, or in any of our other experience that gives any credibility to any astrological idea.
Nevertheless, millions of Americans, from Ronald Reagan to many minimum-wage earners, continue to regulate their daily schedules (to some extent) in accord with the arbitrary and potentially harmful advice. Why? It is essential to remember that a belief doesn't have to be true to be useful. Astrology has flourished because it is a framework within which people can discuss and look for meaning in their lives. Viewed as a social support system, astrology is somewhere between a religion and a psychotherapy.
This fact sheet is substantially based on material prepared by Prof. Rory Coker of the University of Texas at Austin, in cooperation with the Austin Society to Oppose Pseudoscience.