Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax" - Philip Plait (2002)

Part IV. Artificial Intelligence

Chapter 21. Mars Is in the Seventh House, but Venus Has Left the Building: Why Astrology Doesn't Work

"The fault lies not in our stars, but in ourselves."

-Julius Caesar by William Shakespeare

eople say the weirdest things.

A while back, my sister threw herself a nice birthday party. She invited her friends, her family, and her coworkers, and we all had a great time. She had a special setup for kids to play and do artwork, and while I was chatting with some of the other partygoers my daughter ran up to me to show me pictures she had drawn. One drawing in particular caught my eye. I said, "Hey, that looks like an object I study at work!"

A woman next to me asked, "What is it you do?"

"I'm an astronomer," I replied.

Her eyes got wide and her face lit up. "That's so cool!" she said. "I'm terrible at astronomy. I failed it in college."

Well, what do you say to that? I let it slide, and we talked for a while about this and that. A few minutes later, she was commenting on one of the people at the party, and said, "Oh, he's a Libra; all Libras do that."

Ah! Now I knew why she failed astronomy. I refrained from saying anything out loud about astrology, though. I knew better.

The basic premise of astrology is simple: the arrangement of the stars and planets at the time of our birth affects our lives. There is no evidence to show that this is true, but people believe it nonetheless. A 1984 Gallup poll showed that 55 percent of American teenagers believe in astrology. Clearly, astrology is popular.

But that doesn't make it right.

Astrology is like a religion to its devotees. Many religions require faith without proof. In some sense, proof is anathema to these beliefs; you are supposed to believe without needing to see any evidence. Astrology is the same way. If someone tries to show just exactly why astrology doesn't work, you run the risk of being tarred and feathered.

Luckily, I'm willing to take that risk, and I'll say it here, unequivocally and without hesitation: astrology doesn't work. It's hooey, hogwash, and balderdash.

Astrology lacks any sort of self-consistency in its history and in its implementation. There is no connection between what it predicts and why it predicts it, and, indeed, it appears to have added all sorts of random ideas to its ideology over the years without any sort of test of the accuracy of these ideas.

Science is the exact opposite of this. Scientists look for causes and use them to make specific predictions about future events. If the theory fails, it either gets modified and retested or it gets junked. I'll note that science has been spectacularly successful in helping us understand our universe, and that it is perhaps the most successful endeavor undertaken by humans. Science works.

Astrology, on the other hand, doesn't. It makes vague predictions that can always be adapted after the fact to fit observations, as we'll see. Astrologers don't seek causes at all, for a good reason: There isn't any cause to astrology. If you look for some underlying reason, some connection between the stars and planets and our lives, you won't find any. For astrology to sell, buyers must not seek out the fundamental principles behind it, because if they do they'll see that there is none.

To avoid making testable claims about the driving forces of astrology, astrologers rely on mumbo-jumbo to bamboozle the public. If in the rare case they actually resort to specific arguments to defend astrology, they frequently use misleading terms. One web site ( defines the basic force behind astrology by stating:

In some ways, the forces between the Planets involved in Astrology can be simplified into one word: gravity. The Sun has the greatest gravity and the strongest effect in Astrology, followed by the Moon, the Earth's satellite. The other Planets are not truly satellites of the Earth, but nevertheless, they have gravity and so affect the Earth. The Sun controls the Earth's motion and the Moon controls its tides, but the other Planets have their own effects on the Earth-and on the people who live on Earth. Sometimes their influences can be so strong that they outweigh the Sun's energy!

But this makes no sense at all. If gravity is the dominant force, why doesn't it matter if Mars is on the same side of the Sun as the Earth when you are born, or the opposite side? Mars' gravitational influence on the Earth drops by a factor of more than 50 from one side of the Sun to the other. One would think this would be an incredibly important detail, yet it is ignored in most horoscopes.

It's also easy to show that the Moon has a gravitational effect on the Earth (and you) that is more than 50 times the combined gravity of the planets. It seems to me that if gravity were the overriding factor in astrology, the Moon would influence us 50 times more than do the planets.

Astrology apologists sometimes look to other forces like electromagnetism. That's an even worse choice than gravity, since the Sun's effect on us is millions of times that of any other object in the sky. The Sun's solar wind of charged particles is what causes aurorae, and a strong electromagnetic outburst from the Sun can trigger electricity blackouts and even damage satellites. This is a genuine physical effect and will have far more influence on your day than any horoscope.

Astrologers must then rely on some force that is not like gravity or electromagnetism. Some claim this force does not decrease with distance, thus sidestepping the problem of the planets' true distance when you are born. But this opens up a new can of worms: as I write this, more than 70 planets have been discovered orbiting other stars. If the force behind astrology does not decrease with distance, what do we make of those planets? How do they affect my horoscope? And there are hundreds of billions of stars in our Galaxy alone. If they have as much force as, say, Jupiter and Mars, how can anyone possibly cast an accurate horoscope?

Not to mention other bodies in our own solar system. The discovery of Uranus, Neptune, and Pluto threw astrologers into a fit for a while, but they were able to subsume these planets into their philosophy. Interestingly, one web site even mentions the four biggest asteroids: Ceres, Vesta, Pallas, and Juno. These are named after female gods, and the web site gives them feminine attributes after the goddesses for which they are named. Ceres, for example, was the goddess of fertility and the harvest, and astrologically (so claims the web site) has power over a woman's procreative cycle.

But Ceres was discovered in 1801 and named by its discoverer, Giuseppe Piazzi, who happened to choose a female name. Traditionally, all asteroids are now named after women. So are we to believe that an object named rather randomly by a man, and a series of objects named traditionally after women, really have the aspects of the goddesses for whom they are named? What do we do with asteroids like Zappafrank? Or Starr, Lennon, Harrison, and McCartney? My good friend Dan Durda has an asteroid named after him. I don't have any idea how asteroid 6141 Durda (as it is officially called) affects my horoscope personally. If it collides with another asteroid and breaks apart, should I send flowers to Dan's family?

Despite the claims of its practitioners, astrology is not a science. But then what is it? It's tempting to classify it as willful fantasy, but there may be a more specific answer: magic. Lawrence E. Jerome, in his essay "Astrology: Science or Magic," makes a strong claim that astrology is more like magic than anything else (The Humanist 35, no. 5 [September/October 1975]). His basic assertion is that astrology is based on the "principle of correspondence," the idea that an object has some sort of effect on reality by analogy, not by physical cause. In other words, Mars, being red, is associated with blood, danger, and war. There is no physical association there, just analogy. This is how magic works; sorcerers take an object like a doll that, to them, is what it represents, like an enemy king. Anything they do to the doll happens to the king.

Despite our deepest wishes, though, the universe doesn't work on analogy (would Star Trek's Mr. Spock's green blood indicate that blue-green Uranus is the Vulcan god of war, I wonder?). The universe works on physical relationships: The Moon's gravity affects tides on Earth, nuclear fusion in the Sun's core eventually heats the Earth, water expands when it freezes because of the geometry of ice crystals. All of these events pass the test for being real: They have consistant physical rules behind them, they are able to be modeled using mathematics, and these models can be relied upon to accurately predict future events. Also, these events are not subject to interpretation from one person to another.

Astrology isn't like that. The color of Mars may look blood red to one person, but it looks rusty to me (and indeed, the surface of Mars is high in iron oxide-rust). Maybe Mars should represent decay and age, like an automobile in a rainy junkyard, and not the martial aspect of war. Astrological correspondence is up for grabs depending on who uses it. It's not consistent, and it fails the other tests as well.

The shapes of the constellations are another indication of astrology's failures. Technically I am a Libra, having been born in late September. Countless horoscopes tell me that this is the symbol of balance and harmony. Yet look at the constellation: it's basically four rather dim stars in a diamond shape. You can perhaps imagine a set of old-fashioned scales there, implying balance. But it looks more like a kite to me. Should I then be lofty, or an airhead, or prone to windy proclamations (hmmm, don't answer that)? To modern eyes, the constellation Sagittarius looks only vaguely like an archer, but far more like a teapot. The Milky Way is thick and dense in that area of the sky, looking for all the world like steam rising from the spout. Do people born under that sign quietly boil until they explode into a heated argument? The constellation Cancer has no stars brighter than fourth magnitude, making it difficult to see from even mildly light-polluted skies. Are Cancers quiet, faint, dim? Why should the ancient Arabic or Greek constellations be any more valid than mine?

Mind you, the shapes of these constellations are arbitrary as well. Libra looks like a diamond only because of where we are relative to those four stars. Those stars are at all different distances, and only appear to be a diamond. If we had a three-dimensional view, they wouldn't look to be in that shape at all.

And it gets worse. Some stars in the zodiacal signs are supergiants and will someday explode. Antares, the red heart of Scorpius, is one of these supergiants. Someday it will become a supernova, and Scorpius will be left with a hole in its chest. How do we interpret the constellation then?

Apologists for astrology, like many who defend a pseudoscience, try to distract critics rather than actually argue relevant points. Many astrologers point out that astronomy and astrology used to be the same thing, as if once having been part of a physical science legitimizes astrology. That's silly. That hamburger I ate the other day was once part of a cow; that doesn't make me a four-legged ruminant, and it doesn't make the cow any more human.

Another classic astrology defense argues that many famous astronomers were practicing astrologers: Kepler, Brahe, Copernicus. Notice that the list features astronomers from a few hundred years ago. In the end, this argument is just as fallacious as the previous one. Astronomers from centuries past didn't have the scientific basis for astronomy as a physical science that we now have, and, indeed, Kepler was the key person in making that happen. They were still steeped in tradition. Also, it's not clear if Kepler believed in astrology; he was being paid by a king who did, and he was certainly smart enough to understand who buttered his bread.

Astrologers go on to talk about the large number of people who believe in and practice it. Is the majority always right? Fact is fact, unswayed by how many people believe in a falsehood or how fervently they defend it.

Yet astrology is still popular, despite all these devastating claims against it. Why? What weapon do astrologers wield that wipes out all rational and critical claims against them? It turns out their best weapon is us.

When people read their horoscopes, they tend to report an uncanny number of "hits" or correct guesses. How many of us have read a horoscope and been amazed at how well it described our day?

As an experiment, I put my own birth date into a web-based horoscope generator. It reported several things that do indeed describe me: I like to avoid conflicts (despite the tone of this and other sections of this book), I seek a partner who is my intellectual equal, and I prefer to be with other people over being alone. All true. But it also read: "You are a gentle, sensitive person with a deep understanding of people and a very tolerant, accepting, nonjudgmental approach toward life." My wife (who is at least my intellectual equal) nearly split her side laughing when she read that.

But let's take a look at those apparent hits. The description above sounds like a lot of people I know and not just me. The wording is vague enough to apply to just about anybody. This is the basic methodology of the astrologer: wording that applies to everyone. People will pick and choose the parts they want to remember, and that is what reinforces the belief in astrology.

The well-known skeptic and rational thinker James Randi (better known as The Amazing Randi) once performed an experiment in a schoolroom. The teacher told the class that Randi was a famous astrologer with an incredible record of accuracy. In advance the teacher had the students write down their birth dates and place each in a separate envelope. Randi cast a horoscope for each person in the room, placing them in the corresponding envelopes, which were then handed back to the students.

After the students read their horoscopes, Randi polled them about accuracy. The majority of the students thought the horoscopes cast for them were accurate, and very few said they were inaccurate.

But then Randi did an Amazing thing: he asked the students to hand their horoscope to the person sitting behind them (the students in the last row brought theirs up to the front row), and then read their neighbor's horoscope.

The results were priceless. Surprise! Randi had put the exact same horoscope in each envelope. You can imagine the expressions of shock, then chagrin, then embarrassment that crept over the faces of the students. The wording Randi used was vague enough that it applied to nearly every student in the room. He used phrases like "You wish you were smarter," and "you seek the attention of others." Who doesn't?

A specific horoscope might be wrong. A vague one never is, which is why horoscopes are generally very vague indeed. The complementary aspect is the all-too-human ability to forget bad guesses and remember accurate ones. Astrologers rely on our ability to forget the misses in order to continue bilking millions of dollars from the public.

And bilk they do. Astrology is a vast business. Perhaps most appalling is the appearance of a horoscope in daily newspapers across the country. In their defense, the newspaper editors claim they don't believe in it, either, and place the horoscopes in the comics section, indicating how seriously horoscopes are taken. But that's a cheat: the comics are one of the most popular sections of the paper, and the horoscopes are there to increase visibility, not to take away credibility. If the editors don't believe them, why are they there in the first place?

One of the biggest pro-space web sites is They have a huge array of pages devoted to space news, history, opinions, and anything you can think of related to space travel. One day some of the business people in charge decided it would be a bright idea to have horoscopes on the site. They put them up, and within days (or more likely hours) received so many angry e-mails from people protesting the horoscopes that the decision was hastily made to take those pages down. I have no doubt that there was some disconnect between the business end of the site and the content folks (I can imagine the business people figuring astrology has something to do with stars, and that's space-related, right?), but in the end the correct thing was done, and hopefully a lesson was learned. I wish the same could be said about newspapers.

On second thought, maybe I was wrong a moment ago: putting horoscopes in newspapers is not the most appalling aspect here. I think the most disturbing part is the pervasiveness of astrology. It's a numbers game; as long as enough people are fooled, it can be self-sustaining. Stories are told, critical thinking goes out the window, and more people believe. Where does it stop? People laughed when former U.S. president Ronald Reagan's wife Nancy relied on an astrologer to make appointments for meetings when the signs were auspicious, but this is no laughing matter. He was the president of the United States, and his wife was relying on an astrologer! That's just about the scariest thing I can think of. I would hope someone wielding that much power would have just a wee bit more rational thinking ability.

Incidentally, the horoscope cast for me on the web did have more to say, and it sums up this chapter better than anything I could possibly write:

Though you may be as intelligent as anyone, you do not really have a rational, logical approach toward life, and trying to reach you through logical arguments is often futile. Your feelings, intuition, and heart, not your head, lead you, which may infuriate or bewilder your more rational friends. You certainly recognize that there is much more to life than can be explained intellectually and categorized into neat little boxes, and you have an open, receptive attitude toward such areas as psychic phenomena, telepathy, parapsychology, etc.

After reading this chapter, wouldn't you say that sounds just like me?