Of the many systems of personality description and prediction that predate modern psychology, the most popular by far is astrology. The basic hypothesis underlying astrology is quite straightforward: it is based on the notion that the positions and movements of celestial bodies, including sun and moon as well as the stars and planets, at the moment of birth exert a profound inﬂuence on personality and the course of one’s life. This idea dates to the early days of astronomical observation, a time when nothing was known of interstellar distances or of the actual nature of the stars. The recorded history of astrological divination dates back at least 3,000 years to the Chaldeans and Assyrians. The twelve-sign zodiac, so familiar to modern newspaper readers, was already in use in Babylon by about 450 bce.
That twelve-sign zodiac, also known as sun-sign astrology, remains the most popular form of traditional western astrology, distinct from various Asian astrological systems such as the one often encountered by Americans on Chinese restaurant placemats, which bear little relationship to the western form. A horoscope is simply a map of the skies over Earth at the time of one’s birth, divided into twelve zones, or signs of the zodiac. Horoscope is also the name given to a forecast based on that map. Each sign represents the approximate location in the sky (in ancient times) of each zone’s namesake constellation. The paths of the sun, moon, and major planets are then traced through the zodiac, and their locations at the exact moment of birth noted. According to astrologers, this information determines important aspects of an individual’s personality and can be used to make predictions about that person’s future.
Of the many objections that can be made to astrology, perhaps basic astronomy and physics are the best place to start. As every junior-high science student knows, the universe is in constant motion, with celestial bodies forever moving further apart from each other. The resulting changes in bodies’ positions relative to each other are slow and subtle, but they add up over time. Because of a phenomenon known as precession of the equinoxes, for example, key elements of the position of the constellations in the sky have moved westward approximately 30 degrees in the last two millennia. What this means in layman’s terms is that the constellations of the zodiac no longer correspond to the regions of the map named for them. Thus, an ancient Babylonian born on the same day of the year as the reader of this book was born under a different sign, but basic sun-sign astrology has not changed to reﬂect this. Some astrologers are, of course, aware of this and draw their charts according to the sidereal year rather than the solar year, which takes these changes into account.
A further problem arises when other changes in astrological knowledge are considered. By the twenty-ﬁrst century man had discovered several more planets in the solar system that were unknown to the ancient Babylonians, including Pluto, one that was discovered more than two thousand years after the sun signs were designated. Some astrologers have come to include Pluto in their calculations, but they still fail to take into account the many other celestial phenomena that have been discovered in the intervening millennia.
Physics is no more likely to support the basic premises of astrology: gravitational pull, the only logical way for a star to exert an inﬂuence on other bodies, decreases proportionally with distance. It is a matter of fairly simple calculation to demonstrate that smaller objects, including the people present at the delivery, would exert a gravitational pull on the newborn child several orders of magnitude greater than that provided by even the nearest stars. If the physical inﬂuence of the constellations is the basis for astrology, therefore, a system of divination based on the different body types of obstetricians would make at least as much sense.
Another basic objection comes from psychology: given the current state of knowledge about human personality, the suggestion that everyone belongs to one of twelve distinct types seems dubious.
Despite the logical problems, however, astrology remains hugely popular among adults in the United States, with most daily newspapers running a horoscope column. In the late 1980s the Committee for the Scientiﬁc Investigation of Claims of the Paranormal (CSICOP) sent a letter, endorsed by many top scientists, to approximately 1,200 newspapers asking them to add a small disclaimer to their horoscope column simply pointing out that its purpose was entertainment; only eighty papers complied with the request.
The most obvious reason for astrology’s popularity is the fairly common feeling that it “works.” Many people, including those who disdain the newspaper sun-sign columns, believe professional horoscopes to be very accurate and point to their own horoscope, which was astonishing in how well it described them, as evidence of this. The problem is a well-documented phenomenon sometimes called the Barnum effect, named for the circus entrepreneur who famously observed, “There’s a sucker born every minute”; given a sufﬁciently vague, positive personality description, most people will ﬁt it to their own preconceived notions about themselves. This has been demonstrated experimentally many times, and actually makes an excellent classroom demonstration. The class is told that a professional horoscope has been drawn up for each of them, and each student is given a written personality description. The students are then asked to rate how accurately it describes them, on a scale of one to ﬁve. Most students give the proﬁle a ﬁve, often including comments about what a classic Virgo, Taurus, and so on, proﬁle they are. They are then somewhat chagrined to discover that they all received the same vague, generic personality proﬁle.
More solid empirical evidence exists, of course. Professional astrologers believe ﬁrmly in their work and their ability to use charts to understand individual personalities, and so they have sometimes been willing to undergo empirical tests of their skills. In an experimental design that has now been used several times by different research teams, and which astrologers have agreed is a fair test, the astrologers are given thorough horoscope charts for a sample of volunteers, along with the results of psychological personality tests for each of them. Their task is to match up the horoscopes to the correct personality proﬁles, a job which should be very easy for them if the horoscope really provides predictable information about personality. The result is always the same: the professional astrologers can’t reliably pick out a correct horoscope reading.
Despite the fact that there is scarcely a shred of scientiﬁc evidence in its favor, however, astrology continues to be enormously popular. Nowhere was the gap between evidence and practice clearer than in the Reagan White House, where, apparently, Ronald Reagan’s schedule was partly determined via the First Lady’s consultations with an astrologer.
- Carlson, S. “A Double-Blind Test of Astrology.” Nature, 318 (1985): 419–425;
- Clarke, D., and Gabriels, T. “Astrological Signs as Determinants of Extroversion and Emotionality: An Empirical Study.” Journal of Psychology, 130(2) (1996): 131–141.