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Readers: This page is pretty long, because there's a lot to say. To make it easier on you, here's a set of links to the various topics on this page.

Table of Contents

Before I even start, a note: this page is my attempt to show that astrology has no basis in reality whatsoever. Ironically, the Google ads on the right hand side of this page will invariably advertise astrological websites, because Google looks for keywords in a page and serves up "appropriate" ads. It's impossible for me to filter out the swarming mass of astrology ads, so you have my permission to look at them and chuckle.

[Update (July 2011): I've been getting requests to translate this page into other languages, so I'm pleased to present it translated into Spanish as well as Belorussian. Being a semi-monoglot myself, I cannot verify these translations, so please contact the authors if you have specific comments.]


I've avoided the topic of astrology for a long time. Mostly it's for the same reasons I took so long to take on people like Hoagland and his Mars claims: there are just so many ridiculous ideas associated with the topic, I knew that it would be impossible to just dip my toes in. It's either stay out, or dive in all the way.

So: Geronimo!

It's time to tackle the thorny topic of astrology. Why now? Well, for one thing, I've waited long enough. It just seems wrong to avoid talking about the biggest baddest astronomy there is. For another, I wrote an article about astrology for the magazine Night Sky. My editor and I discussed how to do it, and he wanted me to focus on star-sign astrology (the kind you see in the newspapers, for example). I agreed that was good for the magazine article, but it didn't go into the depth I wanted to about astrology in general.

This page is an antidote to that. Astrology is wrong, and I aim to show you why.


Astrology is wrong.

I wanted to put that first, just so we're clear, and to make sure you're paying attention. I'll repeat it later, too.

The Basics

What is astrology?

Taurus the bull
Taurus, the aptly-named Bull
That question is tough, actually. There are lots of flavors of astrology. Sun sign, Vedic, archetypal, natal, Horary... the different kinds of astrology seem to outnumber the stars in the sky. Some of the claims they make are inherently contradictory (some say the moment of birth is important, others say it's the month, etc.), but they all operate under a very broad working assumption: there is some sort of force from the heavens that influences us here on Earth. There are lots of different attributions for this force (some say gravity, some say electromagnetism, some say a force that cannot be measured), but it all boils down to the planets and stars having an effect on people.

If there is an effect, and it's real, it can be measured. That's pretty much by definition. Maybe it's not directly measured on an individual basis; maybe there is only a statistical effect. In other words, the effect cannot be shown for an individual, but only for groups of people (like saying that I cannot know what the weather will be like where I live exactly ten years from today, but there is a high probability it will be clear and sunny that day). But even that can be measured using statistics, and predictions like that can be tested for their accuracy.

First, let's see if there can be any effect from the planets and stars as astrologers claim. Then, after I show you that there not only isn't any, but cannot be any as they claim, we'll take a look at the claims astrologers make about measured effects (I'll give you a hint: they're wrong). Then finally, I'll talk a little bit about the real effect of astrology, and how it is eroding people's ability to think clearly.

Farce of Nature

For just a moment, let's say that there is some force from the planets that can affect us here on Earth. What could it be?

Our choices are limited. Planets are big balls of ice, rock, metal, and other stuff. Their ability to affect us is weak because they are pretty far away. As far as we can tell in science, there are only four fundamental forces: gravity, electromagnetism, and two forces called the strong and weak force. Those last two only work (more or less) on the nuclei of atoms and subatomic particles. It's hard to see how they could affect us on a macroscopic scale (the strong force weakens so rapidly with distance that it's essentially gone by the time you're a few billionths of a meter from the source!).

So we're stuck with either gravity or electromagnetism. Let's look briefly at both.

We know quite a bit about how gravity works on large scales, scales like that of the solar system. Basically, the gravity of an object depends on two things: how much mass it has, and how far away it is. The more massive an object, the stronger its gravity. The closer it is, the more its gravity affects you.

Jupiter and Io
Jupiter and its moon, Io. Note the size difference; Io is the same size as the Earth's Moon (and that black spot is its shadow on Jupiter; Io itself is a little bit to the right).
That's all well and good, but we really need to put in numbers to analyze it. Why? Because, for example, Jupiter has about 25,000 times the mass of the Moon. That's a lot! But it's also about 1500 times farther away than the Moon at its closest. Which number wins in the game of gravity?

In this case, it's distance, by a long shot. I won't go into details here, because I already wrote up a page about gravity and the planets. Read it here to get the actual numbers. But the bottom line is that at best, the gravity from the planets in our solar system is a tiny fraction of the Moon's. So if gravity were the force behind astrology, then the Moon would dominate all the planets combined. Yet it doesn't in any astrologer's horoscope.

So it's not gravity. Could it be electromagnetism?

Gravity depends on mass and distance. Electromagnetism (or just EM) depends on electric charge and distance. The problem here is that most large objects don't have an electric charge! I have a little bit more about this topic here. Electric charges come from charged particles like electrons and protons. But opposite charges attract each other so well that it's very rare to find one without the other nearby, which means that a planet is electrically neutral overall.

Saturn zapping the Earth
An alternative astrological phenomenon

Some planets, for other reasons, do have magnetic fields. But these fields are only strong near their home planet. Jupiter's field is immense, but Jupiter is so far away it has no real effect on us. Furthermore, the Sun is far and away the largest EM source in the solar system. Its magnetic field directly affects us; when there is a gigantic flare, or other explosions on the surface of the Sun, vast streams of charged particles are sent sleeting out. These can interact with the Earth's own magnetic field, causing havoc (in 1989, such an event caused a blackout in Quebec). So if anything, the Sun should be the only source of astrological effects. However, astrologers tend to ignore it or still give the planets the lion's share of the astrological effect on us. Either way, the planets' combined force is miniscule compared to the Sun's. If EM is the force behind astrology, the planets could be safely ignored.

If gravity were the driving force of astrology, the Moon would dominate, but it doesn't. If EM were the driving force, the Sun would dominate, but it doesn't. We've run out of forces!

Astrologers' only hope is to posit some other force, unknown to science. However, that hope is bleak indeed. Why?

As far as we know, every force weakens with distance. An object farther away has lesser force on you than something closer. Yet astrologers claim that all the planets have equal (or at least comparable) effects, so nearby Venus and distant Pluto both exert some sort of measurable tug on you (at least, measurable in the sense that they can affect your life somehow). This means, by the astrologers' own claims, distance must not be a factor with this force. Obviously, mass mustn't either, or else Jupiter would dominate the planets, and poor tiny Mercury would be left out.

But this cannot be right! What about asteroids? These are chunks of rock and metal that also orbit the Sun along with planets. Most asteroids are closer to Earth than the outer planets (not that distance matters to astrologers, remember?), so they should have some effect. The problem is that there are many, many asteroids. My friend Dan Durda has calculated that there are a billion asteroids in the solar system larger than 100 meters in diameter. That's a lot of rock! So why don't astrologers include them in their horoscopes?

And it gets worse for astrology. Astronomers have now found about 150 planets orbiting other stars. These are very distant, certainly, but hey! Distance is no issue. So therefore these planets must affect us too. Now, these are only the planets we've discovered so far. Given how many we've found, and what kind of stars they tend to orbit, it's reasonable to assume that there are billions (billions!) of such planets in our galaxy alone. They're everywhere! Why don't astrologers include them in their horoscopes?

Here's another way to think of it. Astronomers (the real scientists) can determine that the planets are out there due to their real effects on their parent stars. If these planets affect us, as they must according to the astrologers' own set of rules, then why don't astrologers predict them? Why didn't any single astrologer 50 years ago say "There must be planets around other stars, because we can see it in our data!"? They didn't because they can't. Their "data" are meaningless. Again, by the rules used by astrologers, all those planets would simply overpower our own solar system planets, washing out their effects as simply and profoundly as the sound of a nuclear explosion would overpower a whisper.

Remember, and I keep repeating this because it's important-- this is playing by the astrologers' own rules. Either there is a known force, and we can show it doesn't work for astrology, or it's some unknown force that doesn't obey the laws of physics, in which case asteroids and extrasolar planets would dominate astrology, washing out the effects from our own solar system planets.

So it can't be a known or unknown force. That leaves nothing. Astrology doesn't work.

Inaccuracy We Trust

A quarter
Another two-bit prediction
I have talked to many people who claim their horoscopes are accurate. These people routinely say that it predicted something that came true.

But there are several possible logical missteps here! First, was the prediction really that accurate? Did it say something like "you will come into money today" and you found a quarter on the ground? Or was it something specific, like "you will find a quarter on the ground"? The difference is that a specific prediction is rarely right, while a vague one is rarely wrong.

Second, was that horoscope right in everything it said? Did an old friend contact you? Were you able to resolve a thorny issue today? Did you really find love today? In other words, how many predictions were accurate, and how many were not? People tend to remember the hits and forget the misses (which is precisely why "speakers to the dead" like John Edward and James van Praagh do so well-- see here, or here or here).

Still having doubts? My friend and master skeptic James Randi performs a wonderful demo of how easily people are fooled by astrology. He went into a classroom, posing as an astrologer, and cast horoscopes for all the students. He had them read and rate the accuracy, and they almost overwhelmingly rated the horoscopes as accurate. The kicker? He had them pass around the horoscopes, and the students saw that every horoscope was exactly the same. It was worded vaguely enough that nearly everyone in the room thought they were being well-described. The horoscopes were so vague they matched nearly everyone, and so their predictive power was meaningless. It was all in the students' heads.

Astrologers rely on our inability to remember when they are wrong, and our almost unfailing ability to see patterns in random noise (in other words, to pull out something that may just possibly kind of vaguely resemble something that describes us).

Kitt Peak observatory with lightning
What are the odds?
Image courtesy NOAO/AURA/NSF
One other thing. I have a friend who said an astrologer made a startlingly accurate prediction about him (saying he had broken his leg some years before). That would be pretty interesting... except that another friend of mine, a stage mentalist who goes by the name of Banachek once told me another story. He does amazing stage work, calling out numbers people are thinking of, seeing through blindfolds, guessing (with incredible accuracy) the cards people are holding. He once said at a skeptic meeting that occasionally he will ask if anyone in the audience has ever been hit by lightning. Of course, he's not really a psychic, but if someone in the audience has been hit by lightning, they will sure think he's psychic! Imagine the odds of being able to guess that, they'll think. The problem is, the odds approach certainty if you ask enough people. And if he asks and no one pipes up, he just moves on with his act. I'll add that when he did that trick when I was in the audience, I had to smile ironically: someone I knew was once hit by lightning. If I had been a random audience member, would I have rated that as a hit? You bet I would have.

The point is that even a wild guess by an astrologer, even if it's right, may be meaningless. How many times has he said something like that to someone he is reading, only to be denied?

When investigated closely, and with a skeptical mind, astrological claims are smoke and mirrors. In the next section we'll see just such an investigation.

Cause and Defect

So as I showed above, there cannot be an effect on us by any "astrological force", no matter how we assume it acts. No matter what, the evidence contradicts such a claim. Also, many astrological claims, even apparently accurate ones, may be nothing more than sleight-of-hand. But still, that does not mean all astrology is wrong. Is there anything that really shows astrology is bunk?

Yes, there is.

In the spirit of giving the astrologers more rope, so to speak, let's assume that despite all the scientific evidence against such a thing, there really is an effect on us by the planets. If it exists, it must be measurable, and for astrologers to be able to use it to cast horoscopes, their claims must be consistent. After all, if a force cannot be measured, it cannot have an effect on us, and if astrologers say such a force exists, then all their claims must be based on that force, and should be consistent with each other.

Surprise! Astrologers' claims are not consistent. They're not even internally consistent.

I could show you nearly endless examples of how, say, Sun-sign astrology horoscopes (the kind you see in your newspaper) are completely inconsistent with each other. I could even talk about an astronomical term called precession, which shows that Sun-sign astrology is rubbish anyway (you can try reading one page about it if you'd like). I won't bother, because in the end I think all that stuff is distraction; astrologers will always come up with some lame excuse about how their claims are still correct, when that other astrologer's claim is nonsense (of course, the other guy says that too).

So let's cut to it: astrologers claim they get results that are consistent. There have been studies, tests, experiments, all sorts of things to check this claim. The bottom line is, their claims are wrong.

How do I know? Because I read a wonderful paper, a very thoroughly researched, well-documented, and referenced paper, which shows precisely where astrology fails all its tests. This paper is titled Is Astrology Relevant to Consciousness and Psi?", and was written by Geoffrey Dean, a long-time astrology researcher, and Ivan Kelly, a professor of Educational Psychology and Special Education at the University of Saskatchewan.

The paper demolishes, utterly, any notion that astrology has any effect at all. They look at not only direct studies of astrology, but also "meta-studies", tests that are compiled together to improve statistics (a very powerful method that enables researchers to extract much better quality data from tests that are individually too borderline to give good results). As they say in their own paper abstract:

Many tests of astrologers have been made since the 1950s but only recently has a coherent review been possible. A large-scale test of persons born less than five minutes apart found no hint of the similarities predicted by astrology. Meta-analysis of more than forty controlled studies suggests that astrologers are unable to perform significantly better than chance even on the more basic tasks such as predicting extraversion [sociability]. More specifically, astrologers who claim to use psychic ability perform no better than those who do not.

In other words, astrology doesn't work. They detail the cases of people born at very close times and locations, what they call "time twins" (say, two babies born within minutes of each other at the same hospital). Astrologers, of course, would predict many similarities between time twins. But, as Dean and Kelly phrase it so succinctly, "The strong similarities predicted by astrology were simply not there".

This paper goes on with a very careful analysis of the studies, and also very carefully tries to discuss any flaws astrologers might bring up (for example, they use an astrologer's own definition of what a time twin would be). Simply put, the paper is devastating to astrology. It's also not terribly hard to read. Give it a try! I laughed out loud many times when reading it, it was so matter-of-fact in its dissection and eventual destruction of astrology.

Ivan Kelly wrote another paper, called "The Concepts of Modern Astrology: A Critique", which discusses the underlying basis of astrology and its claims, and is similarly devastating in its conclusions. As Kelly says, "We can conclude that not a reliable source of information or knowledge about ourselves...Astrology is part of our past, but astrologers have given no plausible reason why it should have a role in our future...".

I couldn't say it better myself. Oh wait, yes I can: astrology is wrong.

A Call to Harms

So what's the harm? Sure, astrology doesn't work, but it's all in fun, right?


For one thing, it's estimated that hundreds of millions of dollars are spent on astrology every year in the United States alone. That's real money, folks, wasted on something that doesn't work.

For another, astrology promotes the worst thing in the world: uncritical thinking. The more we teach people to simply accept anecdotal stories, hearsay, cherry-picked data (picking out what supports your claims but ignoring what doesn't), and, frankly, out-and-out lies, the harder it gets for people to think clearly. If you cannot think clearly, you cannot function as a human being. I cannot stress this enough. Uncritical thinking is tearing this world to pieces, and while astrology may not be at the heart of that, it has its role.

For a third, and this one irritates me personally, astrology takes away from the real grandeur of the Universe. We live in an amazing place, this Universe of ours, and it's quite fantastic enough without needing people to make up things about it. Astrology dims the beauty of nature, cheapens it.

Hey, you might say, sure it's in the newspapers, but they put it next to comics, right? How seriously do newspapers take it then? My answer is, if newspapers don't take horoscopes seriously, then they shouldn't publish them in the first place. People know that comics aren't real, but not everyone understands astrology has as much legitimacy as "Blondie and Dagwood". Saying their location indicates their rationality is a cop out. Most newspapers in this country don't even have a science section, and science is critical to our daily lives (you're reading this on a computer, right? Do you wear glasses, or clothes, do you brush your teeth, take medicine, invest in tech stocks, drive a car? Thank science for all of those things then). They don't have a science section, but they'll publish horoscopes.

Also, back in the 1980s, Nancy Reagan, President Reagan's wife, consulted an astrologer to make sure that meetings and such were planned on auspicious dates astrologically. Her husband -- the President of the United States -- went along with it. Still don't think this is harmful? Arguably the most powerful man in the world, and he based his calendar on the random and unsubstantiated claims of an anti-scientific nonsense peddler.

I hope I've made my stance clear.

Summing Up

I had a lot to say here! So just to make it easier on you, here are the main points of this page:
  • There is no force, known or unknown, that could possibly affect us here on Earth the way astrologers claim. Known forces weaken too fast, letting one source utterly dominate (the Moon for gravity, the Sun for electromagnetism). An unknown force would allow asteroids and extrasolar planets to totally overwhelm the nearby planets.
  • Astrologers tend to rely on our ability to remember hits and forget misses. Even an accurate prediction may be simple chance.
  • Study after study has shown that claims and predictions made by astrologers have no merit. They are indistinguishable from chance, which means astrologers cannot claim to have some ability to predict your life's path.
  • There is harm, real harm, in astrology. It weakens further people's ability to rationally look at the world, an ability we need now more than ever.


Astrology is wrong.

See? Told you I'd repeat it. That was one astrological prediction you could actually count on.


You can type the word "astrology" into Google, but stand back: you'll get about 11 million pages. I would venture to say that 95% of them (at least!) are garbage. So here are a few that are worth your time.

©2008 Phil Plait. All Rights Reserved.

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