We need to talk about astrology

The science is clear: horoscopes are meaningless, but they aren't harmless.

It brings me no joy to do this. Honestly, I’ve been avoiding it for years. But Capricorn, I can’t stay silent any longer. This is an intervention. You’re addicted to astrology.

On a first date, you crave a quick fix of what’s your sign? When you get a job offer, you’re lost until you check your horoscope for guidance from Io and Europa. When a friend says you’re too emotional, you blame it on the fact that your mom was induced three weeks before your due date.

I’m not just worried about you, Capricorn. I’m concerned for everyone out there with a celestial tattoo. Astrology is a $12 billion industry, and it’s gaining popularity with younger generations. I was shocked to learn that four in ten Americans don’t know that astrology is not at all scientific.

I know what you’re thinking. That’s exactly what a Scorpio would say!

Nice try, but I’m an Aries.

Which is meaningless… but not harmless.

If I were a physicist, I’d rescue you from the Flat Earth Society. If I were a nutritionist, I’d steer you clear of the Tapeworm Diet. As a psychologist, it’s my responsibility to tell you the truth about astrology.

I’m not biased against horoscopes—I’m partial to strong evidence. If you have better data, I’m ready to think again. In the meantime, I hope you’ll listen with an open mind.

They All Got Their Different Minds

Astrologers claim that zodiac signs are important factors in personality. Pisces is loving. Sagittarius is free-spirited. Taurus is loyal (and freaky, according to the renowned stargazer Beyoncé).

These are hypotheses. How would you test them scientifically?

You could start by surveying a group of people about their birthdays and personalities to see how they cluster together.

That’s what a team led by MIT professor Jackson Lu did. They recruited a massive sample—173,709 people. They correlated their zodiac signs with their scores on the Big Five personality traits. And they found zero correspondence.

That’s right… none. Knowing someone’s zodiac sign reveals nothing about their personality.

Let’s start with agreeableness. On a 1-7 scale, how friendly, cooperative, and polite are you?

If you think Libras are peace-loving, you might expect them to score in the 6 range on agreeableness. If you see Scorpios as argumentative, you’d put them around 2.

You’d be mistaken. Scorpios averaged a 5.61 on agreeableness. Libras came in at 5.63. The scores for the other ten signs were all between 5.61 and 5.63 too. Every sign was equally agreeable.

The same was true for the other traits—conscientiousness, emotional stability, extraversion, and openness. On every trait measured, average scores failed to vary statistically by sign:

Astrology doesn’t predict life outcomes either. In a nationally representative sample of over 30,000 Americans, happiness levels didn’t differ meaningfully by sign. Neither did infidelity or divorce rates, which were between 21% and 22% for all 12 signs.

Ok Capricorn, I know this puts you in a tough spot. You realize the data are damning, but you’re still not quite ready to toss out your birth chart. You probably have some questions:

1.       Maybe the participants were trying to debunk astrology. Wouldn’t we see different results among true believers?

That’s one reason why the MIT-led team decided to collect their data in China. Astrology is so popular there that of all mobile internet searches, it’s been one of the top five queries. On the personality survey, 55% of participants were believers. This didn’t affect the results at all: even among the astrology faithful, zodiac signs were unrelated to personality traits.

2.       Wait, but birthdays matter! What about all the evidence that kids with January birthdays end up being better athletes and better students than kids born in July?

You’re right. Birthdays do matter, but it’s not because there’s a connection between zodiac sign and personality. The advantage comes from relative age. When you’re young, being a few months older than your peers makes a big difference. In elementary school, January kids have more mature bodies and brains than July kids. They seem stronger and faster to their coaches—and smarter and more responsible to their teachers—so they get more encouragement and more opportunity. Over time, they develop a cumulative advantage.

3.       I’m a Cancer, and my best friends are Geminis and Leos. Don’t people get along with their sister signs?

Sure… if they think it gives them something in common. Hearing that you share a sign is a form of social glue. In one experiment, people were nearly twice as likely to help a stranger if they had been randomly assigned to learn that they shared a birthday. (Plot twist: they didn’t.) It’s easier to bond with people when you expect to get along with them.

4.       Then why is my horoscope so accurate?

That’s an illusory correlation. Many studies have shown that if you read a horoscope that you think is yours but has actually been randomly assigned to you, you’ll probably still think it resonates. That’s especially true if you’re into astrology: believers are significantly more likely than skeptics to buy into bogus horoscopes.

That’s the Barnum Effect (also known as the Forer Effect). Astrologers write horoscopes to be just specific enough that they feel personal, while still being vague enough to be open to interpretation. Fortune tellers and mediums use a similar trick. So do Myers-Briggs assessments (and yes, it’s past time to abandon the MBTI too).

5.       But the moon’s gravitational pull causes the tides. Can’t celestial objects affect us too?

Not through gravity. The planets exert virtually no gravitational force on humans. The moon’s gravitational force on us is infinitesimally small too (and has nothing to do with water). If you put a pillow on your head, it produces 7 trillion times more force on you than the moon does. An astrophysicist explains this and debunks natal charts too. I beg you to read it—if you understand astronomy, you can’t believe in astrology.

This is the Ending of the Age of Aquarius

If you stop and think about it, the whole idea of astrology is arbitrary. How could the position of the sun, moon, and planets on the day you happened to be born possibly have a permanent effect on your personality?

Of all the factors that shape our personalities, the most influential one is DNA. Twin studies consistently show that the major traits are about 50% heritable. Many genetic variants combine to shape your tendencies, and environmental factors like parenting, peers, and trauma affect how those tendencies are expressed. If you want to understand your personality better, look to your genes and experiences, not to the sky. There’s no plausible pathway through which star alignment upon womb exit can alter your brain or your life.

Zodiac signs are just stereotypes. They’re generalizations about groups that aren’t grounded in reality. In fact, they differ from one country to the next. In the U.S., the most disliked signs are Cancer and Scorpio. We wouldn’t choose to be associated with a deadly disease or a venomous predator. But in China, it’s Virgos who are seen as prickly and disliked the most. Why?

The Chinese character that happened to be used for Virgos translates to “old virgin.” In other words, a spinster. And this brings us to the real harm that astrology can do. It causes discrimination against people whose signs are linked to undesirable traits.

In China, it’s common for people to display their zodiac signs on their resumes and dating profiles. In experiments, simply labeling a candidate as a Virgo rather than a Libra is enough to reduce their odds of getting a job and finding love. Managers don’t want to hire them—and people don’t want to date them.

Even parents are biased against their own children based on zodiac signs. When Chinese kids are born just outside the cutoff of a “lucky” sign, their parents tend to invest less in their education—which leaves them worse off on math and verbal tests.

It’s time to kick your astrology habit. You’re hurting yourself by forming impressions of people based on irrelevant information. And you’re hurting others by holding prejudice against them for something that has nothing to do with who they are. You wouldn’t judge people by their fingerprint type or their blood type, and you shouldn’t judge them by their zodiac sign either.

There’s some evidence that astrology often appeals to people who lack critical thinking skills and want to feel special. I know that’s not you. I think it helps you manage uncertainty. Religion used to play that role for more people, and Marx called it “the opiate of the masses.” The difference is that religion can’t be falsified (scientists can’t disprove the existence of a deity or an afterlife), but astrology has been.

Even if you’re just microdosing for fun, there are risks. Astrology may be a gateway drug: it can open the door to the hard stuff. Research suggests that people who believe in astrology are also more likely to think the Holocaust didn’t happen, the earth isn’t spherical, and 9/11 was planned by the U.S. government. If you’re drawn to one flawed idea, what’s to stop you from embracing others? One day you’re entertaining nonsense about the moon, the next you’re convinced that the moon landing was faked.

Capricorn, I hope you don’t unfriend me for this. But if you do, I’ll get over it. I’m actually a Leo.