“Two things are infinite: the universe and human stupidity.  And I’m not so sure about the universe.”  Albert Einstein

  1. Introduction to Astrology

Astrology is a fascinating example of pseudoscience.  It is particularly interesting because the study of astrology brackets the times preceding and following the discovery of the scientific method.  A definition of astrology is “the study of the movements and relative positions of celestial objects as a means of divining information about human affairs and terrestrial events.”   To ancient observers, it seemed evident that the motion of objects in the Heavens played important roles in conditions on Earth.  A precise knowledge of the calendar – in particular, the summer and winter Solstices and the vernal and autumnal Equinoxes – was invaluable in determining when to plant and harvest crops.  In addition, it was suspected that the position of the Moon might be related to tidal phenomena.

Thus it makes sense that medieval observers would conjecture that conditions on Earth – e.g., the seasons, the tides – might be correlated with (and presumably influenced by) the positions of heavenly bodies.  And even crude measurements showed that heavenly bodies moved in regular cycles.  If we put ourselves in the position of ancient observers, it would have seemed natural that the Earth is at rest, and that all other heavenly bodies revolve around the Earth.  Prior to Renaissance scholars such as Galileo, it appeared unthinkable that the Earth might be moving, much less rotating on its axis.

So, the Sun appeared to revolve around the Earth with a period of one day.   Ancient observers also judged the stars to rotate in fixed fashion about the Earth’s North Pole (in the northern hemisphere) with a period of one day.  The easiest way to understand this stellar motion was to assume that each star is embedded on the surface of a sphere, and that this “celestial sphere” makes one complete revolution around the North Pole once a day.  The celestial sphere is shown in Fig. 1.

Fig. 1: The celestial sphere.  Ancient observers believed that all stars were embedded in the surface of a sphere that made one complete rotation around the pole each day.

The existence of a celestial sphere “explained” why the stars appeared to rotate around the pole daily in fixed locations.  Furthermore, at first sight the stars seem to be unchanging.  Except for anomalies such as supernovae or comets, stars seemed to occupy fixed positions on the celestial sphere.  Viewed from a human time scale, they do not seem to die or decay, unlike living things on Earth.  Medieval observers thus concluded that stars were not composed of the same elements found on Earth.  Ancient observers hypothesized that everything on Earth was composed of four basic elements or essences: Earth, Air, Fire and Water.  Thus it was assumed that the stars were made up of some fifth element, or quintessence.

Now, the stars are not distributed equally around the celestial sphere; there are brighter stars and dimmer ones, and stars also appear in clusters.  If one has a vivid imagination (or ample time to gaze at stars, as shepherds would have), one can arrange clusters of stars into groups called constellations.  Furthermore, one can assign names to these groupings, and with a bit of imagination (let’s amend that – a lot of imagination) one can deduce that each cluster resembles an animal, or some other object.  Figure 2 shows twelve of these constellations seen in the Northern Hemisphere.  As we will see, this set of star clusters has considerable significance in European astrology.  The set includes Taurus (the bull), Scorpio (the scorpion), and Libra (the scales).

Zodiac constellation map with leo virgo scorpio symbols vector illustration
Fig. 2: Twelve clusters of stars or constellations, and their names.

Despite the limited technology at their disposal, early civilizations developed rather elaborate methods to obtain accurate determinations of the positions of the Sun, Moon, stars and planets.  In addition, there were attempts to predict and understand natural phenomena such as lightning, eclipses, comets and supernovae.  All of these efforts were part of what appears to be a universal quest to make sense of the world around us.

As part of this effort to understand celestial phenomena we define the ecliptic, the yearly path that the Sun appears to follow with respect to a stationary Earth.  We find that, as viewed from Earth, the apparent path of the Sun has a slight wobble with a period of about one month.  Viewed from Earth, the Sun takes one year to make a complete circuit of the ecliptic.  Fig. 3 shows the path of the ecliptic; the ecliptic is also shown as a dashed line on Fig. 1.

Fig. 3: The ecliptic (white ellipse) is the apparent path of the Sun (relative to the stars) as viewed from the Earth during one year.  The red curve in the figure represents the celestial equator.

During the course of a year, the Sun appears to move in a regular fashion with respect to the stars.  The Sun crosses the celestial equator (the projection of the Earth’s equator onto the celestial sphere) twice a year, once at each equinox.   Figure 1 shows one such point, the vernal equinox (this occurs in the spring; the autumnal equinox is on the back side of that diagram).  So the Babylonians divided the ecliptic into twelve equal sectors, each of which comprised 30o, and chose the beginning of the cycle as the vernal equinox.

Now, if we were able to see the stars during the day, we would find that during a certain month, the constellation Aries (the Ram) appears to be behind the Sun.  As time passes, the Sun seems to “move” in the sky so that roughly one month later, the Sun would appear in front of the constellation Taurus, the Bull.  This cycle continues: in each month, the Sun will appear in front of a different constellation.  Over the course of a year, the Sun appears to move clockwise through the twelve constellations shown in Fig. 2.

So, the astrological “houses” are named for the constellation that appears to be behind the Sun during that part of the year.  The Sun appears to pass through each of these sectors in order, spending roughly 30 days in each sector.   Now, there is a problem with the definition of the astrological “houses,” which is related to a phenomenon called the precession of the equinoxes.   Nowadays, we realize that the Earth actually rotates around the Sun, and because Earth is not completely spherical, the axis of Earth’s rotation gradually shifts.  It takes just under 26,000 years for the Earth’s rotation axis to complete one full revolution about a direction perpendicular to the plane of Earth’s orbit about the Sun.  The precession phenomenon is shown in Figs. 4 and 5.

Fig. 4: Schematic showing precession of the Earth’s North Pole, compared with Earth’s daily rotation and annual revolution about the Sun.
Fig. 5: Effect of Earth’s precession over time.  Today, at the spring equinox the Sun appears to be in the constellation Pisces; whereas in the year 4600 the Sun will appear to be in Capricorn at the spring equinox.

As a result of this precession, over time the Sun will seem to be located in a given “house” at a different time of year.  For example, today at the spring equinox (March 21), the Sun appears to be in front of the constellation Pisces.  In the year 4600 BCE, the Sun will appear to be in the constellation Capricorn on the spring equinox, as shown in Fig. 5.  Astrologers deal with the precession of the equinox in two different ways.  One group uses what is called sidereal astrology.  In this system, the sign of the zodiac is chosen to be the “house” that the Sun currently occupies today.  In the sidereal system, Pisces is currently assigned to the period March 16 – April 14.  In another millennium, the zodiacal signs will have shifted to different dates, so the sidereal astrology method will change the dates of the various zodiacal signs accordingly.

The common European system is called tropical astrology.  In this system, the zodiacal signs are assigned to fixed dates.  So in tropical astrology, the zodiacal sign for a given date no longer represents the constellation that appears to be behind the Sun.  We adopt the tropical astrology classification in this blog.  In this system, the spring equinox March 21 is defined as the beginning of the zodiac sign Aries.  The other signs follow as shown in Fig. 2 (the length of each sign varies slightly, so that the 12 signs take up a complete year).  Note: since we will show that all astrological systems are based on pseudo-science and magical hokum, it does not matter which system we use.

Thus these twelve constellations, the “signs of the zodiac,” play a determining role in European astrology.  The order and dates of the Hellenistic signs of the zodiac in tropical astrology are: Aries (March 21 – April 20); Taurus (April 21 – May 20); Gemini (May 21 – June 21); Cancer (June 22 – July 22); Leo (July 23 – August 23); Virgo (August 24 – September 22); Libra (September 23 – October 23); Scorpio (October 24 – November 22); Sagittarius (November 23 – December 22); Capricorn (December 23 – January 20); Aquarius (January 21 – February 18); and Pisces (February 19 – March 20).  Fig. 6 shows pictures of the signs of the Zodiac, from the book The Sky: Order and Chaos by Pierre Verdet.

Fig. 6: Representations of the twelve signs of the Zodiac.

The ancients suspected a significance regarding the “house” (i.e., the specific constellation) that the Sun was located in each month.  Since each constellation represented a specific animal (a bull, a fish, etc), an object (scales) or a mythological type (an archer, a virgin), it seemed plausible that one’s personal characteristics or human events might be determined by some aspect of the Sun’s location.  Eventually, astrologers decided that the defining characteristic was the location of the Sun and the planets at the moment of one’s birth.

Now, viewed from Earth, the other planets all orbit in roughly a single plane.  To a good approximation the motion of each planet relative to Earth lies in a plane that is close to the ecliptic.  However, the motion of the planets was much more complicated than the considerably simpler motions of the Sun, Moon or the stars.  A planet would move in one direction relative to Earth, but at various intervals the planet would turn around and appear to  move in the opposite direction.  Thus the planets appeared to “wander” around in the sky (in fact, the word “planet” derives from the Greek word for “wanderer”).

So, astrologers made detailed calculations of the location of the Sun and various planets (relative to the constellations).  A person’s personal characteristics and perhaps their profession would be influenced by the “sign” when they were born.  Thus, if we look up “Taurus” on an astrology Website we find the following personality characteristics. Strengths: Reliable, patient, practical, devoted, responsible, stable.  Weaknesses: Stubborn, possessive, uncompromising. Likes: Gardening, cooking, music, romance, high quality clothes, working with hands. Dislikes: Sudden changes, complications, insecurity of any kind, synthetic fabrics.  Astrologers also produce daily horoscopes, which are supposed to predict good or bad tendencies for various activities, based on the location of celestial objects on that day and a person’s zodiacal sign.  We will discuss daily horoscopes later in this post.

2.  A Brief History of Astrology in Western Europe

Astrology appears to spring from a universal human desire to measure correlations between events, and to understand the relationship between cause and effect.  The regularity of the seasons and the predictable location of celestial objects relative to the Earth led to detailed measurements of the positions of celestial objects.  Based on those measurements, ancient observers hypothesized that there were correlations between celestial locations and human events.  A comprehensive history of astrology would review these practices as they arose in various world cultures, and would discuss the influence of different branches of astrology upon one another.  Since all the various practices of astrology are simply different variants of pseudo-science, we will consider only the current practice of astrology that developed in Western Europe, and is the dominant form currently practiced in America.

Astrology probably appeared in Europe around the 2nd millennium BCE.  At that period, it was correlated with attempts to produce accurate calendars and to chart celestial events in order to predict the seasons.  During this time it seemed natural to ascribe divine intervention to various outcomes, particularly since there appeared to be no viable alternatives.  We know that astrology was being practiced in Mesopotamia in the 2nd millennium BCE.

Following the conquest by Alexander the Great, Babylonian practices were combined with Egyptian astrology.  The epicenter for these practices was the city of Alexandria, which became the home of horoscopic astrology.  It had long been understood that the celestial location of various constellations could be used to determine the seasons.  This knowledge was valuable for planting crops, predicting floods, and other commercial purposes.  Hellenistic astrology thus  concentrated on producing an organized system to categorize celestial events.

Much of the terminology regarding astrology was compiled by Ptolemy, an astronomer/astrologer who lived in Alexandria in the 2nd century AD.  Ptolemy was responsible for The Almagest, which was the definitive treatise on astronomy at that time.  The description of the apparent orbits of planets about the Earth in terms of circles and epicycles formed the dominant description of planetary motion, until it was superseded by the Copernican revolution in the 17th century.

Fig. 7: the Egyptian scholar Ptolemy.

Ptolemy also compiled a treatise on horoscopic astrology called the Tetrabiblos (or “Four Books”).  The Tetrabiblos defined most of the terms used in astrology and, again, dominated that field of inquiry for roughly a millennium.

Fig. 8: a medieval copy of Ptolemy’s treatise on astrology, The Tetrabiblos.

When the Sun appears to be in an area corresponding to a particular sign of the zodiac it is said to be in that house.  In astrology, four of the zodiacal signs are called cardinal signs.  These refer to the signs of the zodiac that correlate with beginning of seasons.  Thus, in the northern hemisphere in tropical astrology, Aries marks the beginning of spring, Cancer the start of summer, Libra the beginning of autumn and Capricorn the start of winter.  The locations corresponding to cardinal signs are called angular houses.

Four of the zodiacal signs are called fixed signs.  The notion is that these are associated with stability.  Thus the four fixed signs of the zodiac are Taurus, Leo, Scorpio and Aquarius, which correlate in the northern hemisphere with the seasons of spring, summer, autumn and winter, respectively.  Fixed signs correlate with what are termed succedent houses (from the Latin for succeeding, since these follow the angular houses).

The remaining four zodiacal signs are called mutable signs.  These are Gemini, Virgo, Sagittarius and Pisces.  In the northern hemisphere, these mark the end of spring, summer, autumn and winter.  The houses associated with the mutable zodiacal signs are called cadent houses (from the Latin, the source of the word cadet or younger son).

Since astrology was developed in medieval times, it is not surprising that this field was also associated with the four classical elements Fire, Earth, Air and Water.  Thus (quite arbitrarily) each house is assigned to one of the classical elements, in sequence, and each element in turn is associated with one aspect of human characteristics.  Thus, the 1st, 5th and 9th houses (Aries, Leo and Sagittarius) are associated with Fire triplicity, and according to Wikipedia this is related to “Identity”; the 2nd, 6th and 10th houses (Taurus, Virgo and Capricorn) are associated with Earth triplicity, which is related to “Material”; the 3rd, 7th and 11th houses (Gemini, Libra and Aquarius)) are associated with Air triplicity, which is related to “Social and Intellectual”; and the 4th, 8th and 12th houses (Cancer, Scorpio and PIsces) are associated with Water triplicity, which is related to “Soul and Emotional.”

3.  Early Connections Between Astronomy and Astrology

The fact that celestial events were correlated with the seasons and with phenomena like the tides led to organized efforts to calculate the motion of the Sun and planets to ever-increasing accuracy. In many cultures, a priesthood developed that claimed to be able to interpret celestial events (or even better, to predict them).  Many medieval rulers relied on astrologers to predict eclipses, or to detect comets and supernovae, and to “interpret” what events would be caused by them.  Also, astrologers attempted to correlate the birth dates of rulers with certain celestial events, in an effort to “prove” that the reign of a particular king was fore-ordained.  Medieval astrologers were often among the most highly-regarded academics, and could wield considerable political influence.

In medieval days, there was no significant difference between astrology and astronomy.  Over time, one branch of astrology eventually transitioned to astronomy: the scientific study of celestial mechanics.  Ancient civilizations made progressively more precise measurements of the locations of the Sun and the planets.

Eventually this study led to scientific theories of the motion of planets, stars and the Earth.  A crucial step in this development was Copernicus’ heliocentric hypothesis that all of the planets moved in circular orbits about the Sun.  This notion was further modified and quantified through seminal advances such as Kepler’s Three Laws of Planetary Motion, Newton’s Laws of Motion and Newton’s Law of Universal Gravitation.

A parallel field of inquiry remained in the province of pseudoscience and magical thinking.  A central feature here was the belief that celestial events played a determining role in terrestrial results.   Thus, primitive cultures might believe that eclipses or comets were harbingers of impending changes (primarily negative ones) that would affect individuals and/or society.  As these ideas were expanded, hypotheses developed that an individual’s personality and fate were affected by the precise locations of the Sun, stars and planets at the time of one’s birth.

A historical discussion of astrology is confounded by the fact that what we now consider the “scientific” roots of astronomy and the “magical” aspects of astrology were inextricably linked in medieval times.  For example, development of instruments to make precise determinations of the orbits of planets could be used to test scientific hypotheses regarding the causes of planetary motion, but they could also be used to acquire progressively more “accurate” data for horoscopes.

In the 17th century, many people now celebrated as early scientists also were active in astrology.  For example, the Danish observer Tycho Brahe made the most precise measurements of celestial events, in the years immediately preceding the discovery of the telescope.

Fig. 9: Danish astronomer Tycho Brahe.

Brahe’s measurements, at the time significantly more precise than any prior astronomical data, led the way to an accurate description of the elliptical orbits of planets about the Sun.  At the same time, Brahe served as an astrologer for the royal court of Denmark, where he constructed horoscopes for a number of eminent persons.

Johannes Kepler worked as an assistant to Brahe, and he obtained access to some of Brahe’s planetary data during Brahe’s life, and then the bulk of Brahe’s measurements following the death of his employer.  Using this data, Kepler derived his Three Laws of Planetary Motion.  This showed that the planets moved in elliptical orbits about the Sun, with the Sun at one focus.  Kepler’s Laws helped to provide the foundation for Newton’s universal law of gravitation.  However, Kepler’s main motive in developing laws for planetary motion was to provide more precise data for astrological purposes.  Kepler had been practicing astrology ever since his student days at Tubingen, where he cast horoscopes for his fellow students.  He also served as an astrologer to the Habsburgs.

Fig. 10: Johannes Kepler

We tend to regard Galileo as the first “modern” scientist.  Galileo clearly understood and championed important elements of the scientific method.  His experiments rolling balls down inclined ramps allowed him to deduce what is now called Newton’s First Law of mechanics.  Introduced to telescopes by the Dutch, he constructed his own telescopes and made advances in optical technology, and he used his telescope to discover several of the moons of Jupiter.

Galileo clearly understood the importance that scientists communicate their results to each other and to the general public.  He wrote two seminal popular books explaining the scientific method.  The first, Dialogue Concerning The Two Chief World Systems, reviewed the difference between the Ptolemaic and Copernican models of the Solar System.  The second, Dialogues Concerning Two New Sciences, compared the Aristotelian vs. Galilean models for the dynamics of bodies.  The title page of that book is shown in Fig. 11.  It is notable that Galileo published these two books in Italian, rather than in Latin, which until that time had been the preferred language for all academic works.

Fig. 11: Title page of Galileo’s Dialogues Concerning Two New Sciences, 1638.

However, even Galileo practiced astrology during his tenure as an academic at Pisa, Padua and Florence.  During his time in Florence Galileo served as an astrologer for the Medicis.  At this time in history, what we now consider astronomy and astrology were still intertwined.  In this post we will separate the “scientific” aspects of this research from the “magical” ones.  When we discuss “astrology,” we will focus on the assertion that one’s personality, and events in an individual’s life, are determined or substantially affected by celestial events.

4.  The Motion of Celestial Bodies

We could go on at length to discuss various aspects of astrology.  However, from a scientific point of view this is all a waste of time, since astrology is based on a series of medieval assumptions that we now know to be false.  For example, it is now clear that the Earth is not the stationary center of the Universe, as assumed by astrologers.  The motion of heavenly bodies is governed by Newton’s Universal Law of Gravity, which states that all pairs of bodies experience a mutual attractive gravitational force that is proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between their centers.

Thus (neglecting other sources of gravitational attraction), the Earth and Sun will revolve around their mutual center of mass.  However, the mass of the Sun is so much greater than the mass of any planet that to a good approximation we can assume that the Sun is stationary, and that all planets move in elliptical orbits with the Sun at one focus.  We must make corrections to this simple picture to take account of the mutual attraction of planets to one another; however, the fact is that the Earth essentially revolves around the Sun, while the Moon revolves around the Earth.

Furthermore, the Earth rotates on its axis once a day.  This accounts for the apparent daily rotation of both the Sun and the stars around the Earth.  Although distant stars are moving relative to the Earth, that motion is sufficiently slow that in most cases, the stars can be considered stationary.  Rather than being embedded in a “celestial sphere,” different stars are in fact located at vastly different distances from one another and from the Earth.  And stars are moving at very different rates of speed.  So the “constellations” are not composed of groups of stars fixed on the surface of a celestial sphere: they are random collections of stars that can be extremely distant from one another.  Because the stars comprising a constellation could be moving at greatly different rates and in different directions, over time constellations will change shape; and eventually, certain constellations will even disappear.

Therefore, the Earth is not the center of the Universe, and all celestial bodies do not revolve around the Earth.  So the notion that the Sun moves through a series of “houses” as it revolves around a stationary Earth simply makes no sense – it is a vestige of a medieval world-view that is completely discredited.  As we have noted, there is no significance to the various constellations.

A puzzling feature of early astronomy was the apparent irregular motion of the planets.  In particular, planets appeared to change direction from time to time.  In astrology, great significance was attached to the apparent position of the planets among the stars.  However, we now understand that the “wandering” of the planets is an artifact of the assumption of a stationary Earth.  Once we adopt a heliocentric picture of the Solar System, where all planets move in elliptical orbits about the Sun, the apparent retrograde motion of planets is easily explained.  Figure 12 shows two planets in circular orbits around the Sun.  We know that the greater the distance of a planet from the Sun, the longer the rotational period.  The dots show the positions of the two planets at five different times.  The graph on the right shows the location of the outer planet as viewed from the inner planet.  The retrograde relative motion occurs because the angular velocity of the outer planet is smaller than that of the inner planet.

Fig. 12: Motion of two planets about the Sun.  The outer planet has a longer period than the inner planet.  Positions of the planets are shown at five different times; the curve at right shows the apparent trajectory of the outer planet as seen by the inner planet.

Western astrology is based on the assumption that two people born at exactly the same date should have similar life histories.  This is also supposed to be true for people born on the same date but in different years.

However, in their book Debunked, Nobel Laureate Georges Charpak and Henri Broch point out that, in the course of one year, the Earth’s location has moved roughly 22,000 miles.  Over a 40-year period, the Earth has moved more than 780,000 miles, while the stars have moved a much smaller distance.  Thus the idea that the Sun occupies an identical position every year is simply fallacious.

Another incorrect assumption of astrology is that one’s horoscope should be strongly correlated with the four “classical humors.”   Although the ancients believed that all matter was composed of admixtures of Earth, Air, Fire and Water, we now understand that matter is made up of molecules which themselves are composed of atoms.  Once one is familiar with the atomic theory of matter and with modern chemistry and biology, it is clear that the “four classical elements” model is hopelessly naive.  In addition, spectroscopy allows us to determine the composition of stars.  We find that stars are composed of the same elements as are found on Earth (predominantly hydrogen gas, with contributions from helium and trace additions of heavier elements).

We also understand the mechanism that determines eclipses, and we are able to predict them with exceptional accuracy.   Eclipses and comets are not connected with either positive or negative events in one’s life.  Nor are lightning, tornadoes or any other meteorological events  portents of either positive or negative results (unless, of course, one is struck by lightning or a tornado).

The field of astrology resulted from efforts to understand the cause and effect of terrestrial phenomena, and to measure celestial events and correlate them with events in human lives.  But this effort was fatally flawed because it was based on the incorrect assumption that the Earth was the stationary center of the universe.  We now understand that astrology is nothing more than a collection of medieval mumbo-jumbo that has no scientific basis.  The “laws” of astrology contradict our modern understanding of mechanics, the atomic theory of matter, and cause and effect, among other things.

There is absolutely no known scientific mechanism whereby events in one’s life could be influenced by the precise alignment of stars, planets and the Sun (as seen from Earth) at the moment of one’s birth.  For that matter, why should the moment of birth be more important than the instant of conception?

5. Science Vs. Pseudo-science

Astrology offers a unique opportunity to contrast science with pseudoscience.  As we have mentioned, until the development of the scientific method, astronomy and astrology were considered to be two co-equal branches of inquiry.

So let us review some aspects of the scientific method.  First, through careful observation of natural phenomena, one formulates a testable hypothesis.  This hypothesis is initially an informed conjecture regarding the nature of a physical system.  From the hypothesis, one identifies a prediction that is capable of being tested.   One then devises an experiment that will test that prediction.  Scientific predictions must be falsifiable – that is, one must be able to devise an experiment whose possible outcome conflicts with the hypothesis.

A series of tests are devised that can either prove or disprove the hypothesis.  Ideally, an experiment should be able to vary only a single aspect of a system while keeping all other aspects constant.  In order to insure that experiments are reproducible, scientists should communicate the results of their experiments to the public.  They should provide sufficient details of their experiments that other investigators could reproduce their results.

By undertaking a series of tests of hypotheses, and with scientists publicizing their results and collaborating with one another, those hypotheses with successful predictions will eventually reach a point of high confidence among the scientific community.  At this point the hypothesis will become a theory.

The field of astronomy presents some difficulties to researchers, since it is difficult to conduct controlled experiments on celestial bodies.  Nevertheless, hypotheses such as Kepler’s Three Laws of Planetary Motion can be tested by obtaining progressively more precise data on the positions of the planets.  Note that by sharing new experimental techniques with scientific colleagues, one can test hypotheses with increasing precision.  Thus we see that application of the scientific method will lead to progress.  Increasingly precise experiments allow hypotheses to be tested more rigorously; and increased precision also leads to the development of new hypotheses.

Let us compare modern astronomy and astrophysics with astrology.  As we have mentioned, at the time of Kepler these two areas were considered as equally valid.  However, over the past 400 years one has seen incredible advances in astrophysics.  Space-based detectors such as the Hubble Space Telescope, and the manned landing on the Moon, are only two examples of the tremendous power of the scientific method.  And what about astrology?  Although we can now make exquisitely precise measurements, there have been essentially zero “advances” in astrology since the 1600s.  Proponents of sidereal astrology and tropical astrology continue to debate which method is superior (spoiler alert: both techniques are bogus).  This is a characteristic of pseudoscience — it never advances, is never proven, and does not contain falsifiable statements (or if it does, those claims are falsified, but the proponents ignore the falsification).

6.  Scientific Tests of Astrological Predictions

In 2003, a comprehensive study was made of over 2,000 babies born in March 1958.  Their development was monitored at regular intervals.  More than 100 different characteristics were measured, “including occupation, anxiety levels, marital status, aggressiveness, sociability, IQ levels and ability in art, sports, mathematics and reading — all of which astrologers claim can be gauged from birth charts.”  The data were analyzed by Geoffrey Dean and Ivan Kelly.  The researchers found absolutely no correlation among the tracked individuals beyond chance for any of these variables.

Another test of astrology was carried out by nuclear physicist Shawn Carlson in 1985 (Shawn Carlson, A Double-Blind Test of Astrology, Nature 318, 419 (1985).  Carlson recruited 28 people who had been nominated as expert astrologers by the pro-astrology National Council for Geocosmic Research.  The “experts” agreed to match 100 natal charts to profiles generated by the California Psychological Inventory.  This double-blind study tested whether the astrologers could match psychological traits to the birth history of the individuals.  Not only did the astrologers do no better than chance in matching the psychological traits to the birth, but the astrologers gave random results even in cases where they indicated strong confidence that they were correct.  The results were published in the journal Nature.

In a 1989 book, Probabilities in Everyday Life, John D. McGervey carried out a study of leading scientists.  He was investigating whether successful scientists were born more frequently under astrological signs that were supposedly favorable to science.  McGervey found no correlation between success in science and particular astrological signs.

We see that scientific studies find no correlations between birth date and various outcomes.  Furthermore, “expert” astrologers are unable to predict a person’s birth date based on their psychological profiles.  As we have shown, the entire notion of the Sun “moving” through various constellations is a result of the fallacious idea that the Earth is the stationary center of the Universe. Astrology has been proved to have no scientific validity and no predictive power, thus we can confidently claim that astrology is pseudoscience.

7.  Why Do People Believe In Astrology?

A 2014 study, the Chapman University Survey on American Fears, found that about 13% of Americans agreed with the statement “I believe astrology is real” (note: the percentage can vary according to the precise wording of the question; it can also change over time.  We have found surveys where the percentage of Americans “believing” in astrology ranges from 10% to 25%).  In general, Democrats were more likely to believe in the paranormal than Republicans.  For example, in response to the “astrology” question roughly twice the percentage of Democrats responded positively than did Republicans.

Horoscopes are widely published in various newspapers and online, although generally they are accompanied by a disclaimer “for entertainment purposes only.”  One reason that people believe in astrology is that they are persuaded that the daily or monthly horoscopes are accurate.  This is an example of a phenomenon called confirmation bias.  One example of this phenomenon is that people tend to selectively remember predictions that turn out to be true, while forgetting those that are false.

In 1948, psychologist Bertram Forer gave his students a personality test.  He then presented subjects with what was described as a unique personality analysis based on their tests.  He asked the students to rank this analysis on a scale of zero (poor) to 5 (excellent), based on how well it described their personality.  The average rating from the students was 4.26 (that is, the analysis was 85% accurate).

In actuality, every student was given exactly the same “personality analysis,” reproduced here: “You have a great need for other people to like and admire you. You have a tendency to be critical of yourself. You have a great deal of unused capacity which you have not turned to your advantage. While you have some personality weaknesses, you are generally able to compensate for them. Disciplined and self-controlled outside, you tend to be worrisome and insecure inside. At times you have serious doubts as to whether you have made the right decision or done the right thing. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations. You pride yourself as an independent thinker and do not accept others’ statements without satisfactory proof. You have found it unwise to be too frank in revealing yourself to others. At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved. Some of your aspirations tend to be pretty unrealistic. Security is one of your major goals in life.”

The ”unique personality analysis” was cobbled together by Forer from several horoscopes.  As is obvious, the statements here tend to be vague and could apply more or less equally to everyone.  Similar studies have been repeated several times, and it has been found that the following factors are associated with high ratings from subjects:

  1. The subject believes that the analysis applies only to them;
  2. The subject trusts the authority of the evaluator;
  3. The analysis lists mainly positive traits.

With horoscopes, items (i) and (iii) are generally true, and people will tend to trust statements if they come from authority figures who identify as psychics or mystics.

Another reason why Americans believe in astrology is that they are inclined to accept “New Age” notions that ancient cultures were repositories of great wisdom (particularly if they are associated with the occult).  Astrology buffs place a great deal of emphasis on the fact that this field is based on “the wisdom of the ancients.”

With respect to quasi-scientific theories such as astrology or traditional medicine, it is important to remember that medieval hypotheses were often wildly wrong.  Prior to the development of the scientific method, ancient cultures had profound misconceptions of physics, chemistry, biology and medicine.  For example, plants used in traditional medicine can contain effective chemicals against particular diseases.  On the other hand, they could well have no effect on a disease, or they can contain toxic materials.

We now know that remedies such as homeopathy are based on “fundamental principles” that are basically nonsense (see our blog post on this topic).  Similarly, scientific tests of astrology show that it is not valid.  In addition, there is no known physical mechanism by which the location of planets and stars at the moment of birth could influence human events.  So, another synonym for “wisdom of the ancients” is – ignorance.

Astrologers make strong claims as to their abilities, and are able to convince many people that they have access to special knowledge.  A particularly troubling example was astrologer Joan Quigley.  After John Hinckley attempted to assassinate President Ronald Reagan in 1981, Quigley told Nancy Reagan that she could have predicted this event based on astrological charts.  Mrs. Reagan believed Quigley, and for a time Quigley was deputized as the secret White House astrologer.  Apparently several of President Reagan’s meetings and actions were shifted in accordance with Quigley’s claims that these were “propitious times” for such events. Of course, Quigley’s assertions were nonsense, but this situation continued until 1988 when Reagan’s chief of staff Donald Regan revealed this arrangement.

Quigley’s assertions are typical of astrologers, who frequently resort to “post-dictions,” asserting that momentous events in the past would have been predicted by astrologers.  I have no psychic powers whatsoever, but I will make some predictions for the coming year that I am confident will be fulfilled.

  • A beloved celebrity will pass away.
  • A calamitous natural event will occur in the world (I could be more specific, and say in the U.S.)
  • A mass shooting or terrorist event will occur in the Western United States.

Another negative aspect of astrology is that one finds significant variation in daily horoscopes compiled by “expert” astrologers.  A skeptic collected horoscopes from various newspapers or websites on the same day (Dec. 20, 2010) all for the same zodiac sign, Taurus.  Here they are:

Horoscope #1: “You need bigger and longer hugs than usual today, Taurus. A powerful force is moving through your life and trying to shake things up. Don’t stoop to the level of petty argument and verbal sparring. The more you resist the opposition, the more stubborn and unwieldy the situation becomes. Make sure you have a good hold on your emotions before you leave the house.”

Horoscope #2: “Be careful what you agree to over the next two or three days because the approaching lunar eclipse will blur the line between fact and fantasy. This is not a good time to be reckless with your money, or your reputation.“

Horoscope #3: “Although the fun element will be lacking almost from start to finish, this is certainly a useful day. Don’t be surprised if you notice some very tiny changes over an ongoing matter. These nudging or very slight improvements might not be much to celebrate, but they will indicate further improvements to come!”

Horoscope #4: “Stay on top of your bank account and your bills today because something unexpected might be taking place. This could affect inheritances, shared property, insurance matters, or anything you hold jointly with others. Make sure you aren’t overdrawn. (Nobody likes surprises like that.)”

Horoscope #5: “Focus on your domestic scene. Get together with friends or relatives. Calm down and take a step back. You can’t win and they won’t listen.”

The horoscopes above are similar in some ways, and quite different in others.  First, they are deliberately vague and often refer to subtle changes (“A powerful force is moving through your life …  you notice some very tiny changes over an ongoing matter … very slight improvements … will indicate further improvements to come … something unexpected might be taking place.”)  Note that these statements could refer to many potential situations, and could refer to events far in the future.

Note also that individual horoscopes are quite different.  This is remarkable, as they supposedly are all influenced by identical celestial events.  One of the only things these horoscopes have in common is that several of them refer to money – that is hardly surprising for a horoscope printed during the Christmas holiday season.

A final argument advanced by proponents of astrology is that even if it is not true, it provides a beneficial tool that individuals can use for self-analysis and spiritual guidance.  This is an extremely unpersuasive argument (identical claims are made for other “wisdom of the ancients” mumbo-jumbo such as Tarot cards and the I Ching).  Many self-help guides can be beneficial and can provide spiritual benefits, without requiring that one believe in things that are patently false.  Your local bookstore likely has entire shelves full of such material.

Apparently astrology is currently popular with millenials.  Articles such as the one by Julie Beck in The Atlantic in January 2018 (Julie Beck, The New Age of Astrology).  One of her subjects, a lawyer named “Sandhya,” downloaded an astrology app on her cellphone.  After “Jupiter entered Leo” in July 2014, she got a new job and met her future husband.  “My life changed dramatically,” she says. … But I followed what the app was saying. So I credit some of it to this Jupiter belief.”

Ms. Beck provides remarkably unconvincing arguments for devotees of astrology.  “If the “astrology is fake but it’s true” stance seems paradoxical, well, perhaps the paradox is what’s attractive. People feel powerless here on Earth, others said, so they’re turning to the stars. Of course, it’s both.”

Gabriela Barkho, in The Observer, points out that some astrology online sites are raising big cash from Silicon Valley investors.  The astrology app Co-Star recently raised $5.2 million in venture cash to produce an Android version of its astrology app.  She also claims that Amazon has begun offering product recommendations to its Prime customers based on their astrological signs — say it ain’t so, Jeff Bezos!

There is some evidence that the LGBT community is now buying into astrology.  Rosa Lyster, who had a column in the online women’s website The Hairpin, has written columns such as “Astrology is Fake, but Leos are Famous.”  Her columns contain statements such as “Leos are famous. I don’t mean that Leos are disproportionately represented in the entertainment industry, although they are … It’s true that they can be easy to spot, and that their self-presentation is often touchingly on-brand.”  Ms. Lyster’s writings are replete with categorical statements that show no sign of any serious attempt at verification.

It is possible that people accept these astrological narratives because they provide comforting claims that your personal characteristics are pre-determined.  Of course you hate change – you’re a Taurus!   But why accept these glib claims that perpetuate medieval misunderstanding  of the world around us, are contradicted by science, and that make statements which are demonstrably false?

Assertions about astrology have evolved as science has demonstrated that it is false and worthless.  “Astrology is absolutely true and has been verified … well, perhaps we don’t have definitive tests but astrology is almost certainly true … OK, astrology has been debunked, but you can still use it and it will help you.”  This is a classic example of Neil deGrasse Tyson’s description of skepticism vs. denial: “A skeptic will question claims, then embrace the evidence.  A denier will question claims, then reject the evidence.

As scientific evidence against a particular viewpoint mounts, the defense of that viewpoint changes, but the conclusion remains the same.  One sees exactly the same revisionist arguments from evolution deniers (see our blog posts on this topic).  Over time, the arguments cange from “there is no evidence for evolution, it violates some basic laws of science, and no transitional forms have been found”, to “OK, there is some evidence for evolution but there is a lack of transitional forms,” to “of course micro-evolution is real, but we reject macro-evolution”).  One sees an analogous pattern in climate-change denial (see our blog posts on this topic).  Arguments change from “there is no global climate change, it’s a hoax” to “OK, there is global climate change but it is perfectly normal and not caused by humans” to “we are seeing global climate change and much is caused by humans, but it would cost too much to do anything about it”).

Astrology is a pseudo-science.  The “principles” of astrology have no basis in modern science, and it is a result of serious misconceptions by ancient observers.  You should not rely upon any of its “predictions,” and you most certainly should not give any money to people claiming to be professional astrologers – your money will be wasted and the advice you receive will be bogus.

Source Material:

Wikipedia, Astrology:
Debunked!  Georges Charpak and Henri Broch, Johns Hopkins University Press, 2004
The Sky: Order and Chaos by Pierre Verdet.  New Horizons, 1992
Wikipedia, Astrological Sign:
Wikipedia, Ptolemy:
Wikipedia, Tycho Brahe:
Wikipedia, Johannes Kepler:
Wikipedia, Kepler’s Laws of Planetary Motion:
Wikipedia, Galileo Galilei:
Geoffrey O. Dean and Ivan W. Kelly, Is astrology relevant to consciousness and psi?  Journal of Consciousness Studies 10, 175 (2003).
Shawn Carlson, A Double-Blind Test of Astrology, Nature 318, 419 (1985).
John D. McGervey, Probabilities in Everyday Life, Ivy Books, 1989.
Chapman University Survey on American Fears, 2014:
Wikipedia, Confirmation Bias:
Relativity and Horoscopes Debunked: Relatively Interesting Website, Oct. 2018:
Julie Beck, The New Age of Astrology, The Atlantic, Jan. 2018.
Gabriela Barkho, Here’s Why Big Tech Wants In on the Current Astrology Craze, Observer, 4/18/2019.
According to Amazon’s New Horoscopes, The Stars Want You To Go Shopping, Kaitlyn Tiffany, Vox 4/9/2019:
The Hairpin (feminist Web site)
Rosa Lyster, “Astrology is Fake, but Leos are Famous”, The Hairpin, July 2017.
Rosa Lyster, “Astrology is Fake, but Taurus Hates Change”, The Hairpin, April 2017.