Your zodiac sign is probably wrong. Here’s how to find the right one

As a teenager, I loved reading my horoscope in gossip magazines. But even then, my friends and I knew it was absurd. For us, it was a fun hobby for bored teenagers. So I was surprised when my hairdresser recently asked me my astrological sign. When I shared my opinion on astrology and horoscopes, she simply responded, “Typical Taurus.”

Astrology currently knows a remarkable renaissance– especially on social media, where posts about “Gemini”, “Leo” and “Virgo rising” are omnipresent. This trend may partly reflect how much people want to identify with personality types and, in doing so, gain insight into an uncertain future. And perhaps surprisingly, many articles on astrology come from people who consider themselves scientifically inclined.

How is this possible? Today, modern science and astrology contrast sharply. There is no proof that your sign actually affects your everyday life. However, the origin of horoscopes is not completely unscientific. It’s actually a story that begins with careful observation of the cosmos and the creation of a calendar system thousands of years ago in the Middle East.

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What exactly are zodiac signs?

The signs of the zodiac, considered by many people to be the foundation of modern astrology, are based on 12 constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. These are by no means the only constellations visible in the night sky. In 1922, the International Astronomical Union (IAU) officially recognized 88 constellations, including those associated with the zodiac and other well-known examples like the Big Dipper.

Thousands of years before the creation of the IAU, people in ancient Mesopotamia were thinking about constellations. They attached particular importance to those who were in the apparent path of the sunalso known as the ecliptic.

Thanks to Mesopotamia’s geographic location, it has historically experienced very consistent weather conditions. There is a rainy season and a dry season. Wind direction can also be predicted based on the time of year. And because certain constellations are visible in the night sky at different times of the year, people may have believed that there was a connection between the stars and these seasons.

This idea is not so far-fetched: after all, scientists now recognize that the sun and moon do influence Earth events such as weather and tides. But distant stars, as we’ll see later, are a different story.

Toward the end of the fifth century BCE, Babylonian astronomers divided the ecliptic into 12 equal sections of 30 degrees each, analogous to the 12 months of their calendar of 30 days each. In doing so, they developed the first known astronomical coordinate system. They assigned each section a constellation located in the night sky along the ecliptic at that time of year.

This is how astrology began. Zodiac signs and their associated superstitions spread from Mesopotamia to Greece and Rome and eventually became part of European tradition.

Times change, and so do astrological signs

In retrospect, it doesn’t seem that far-fetched that people in ancient or medieval times believed that constellations influenced us. What I don’t understand is how this belief has persisted to this day.

We now know much more about astronomy, physics and celestial mechanics. For example, scientists have long understood that constellations are made up of objects that are sometimes very distant from each other and have no connection to each other except that they appear close to each other from our vantage point here on Earth.

Additionally, their distance from Earth is so great that, unlike the Moon or Sun, they cannot actually influence our planet or us. Stars are gigantic fusion reactors located light years away and do not shape our personality or the events of our lives.

If you are reading this article, I assume you do not believe in astrology. But if you find yourself talking to someone who is addicted to horoscopes, here are three scientifically-backed points you might bring up:

There are actually 13 signs of the zodiac. If you look at the constellations along the ecliptic, you will find not 12 but 13 over the course of a year. Ophiuchus, the serpent bearer, has been forgotten. Or rather, it was probably intentionally excluded from the list because it did not fit into the Babylonians’ 12-month system.

Not all zodiac signs correspond to a month. The sun crosses the boundaries of the zodiac signs for different durations while traveling through the ecliptic. For example, the sun only crosses the boundaries of the constellation Scorpio for six to seven days, while it takes 44 to 45 days to cross the boundaries of the much larger constellation Virgo.

Zodiac signs change over time. More specifically, the Earth’s axis of rotation oscillates like a top, a phenomenon known as precession. This movement changes which constellations appear in the ecliptic at what time of year. While the constellation Aries was visible in the ecliptic from March 21, according to Babylonian time, today the constellation Pisces appears instead on that day.

Are you still determined to find your star sign?

A scientifically correct zodiac system exists. In it, each constellation is located in the modern day ecliptic.

This is very different from the system that is still used in astrology today. But don’t worry, Scientific American is not going to print horoscopes based on the corrected zodiac – except, perhaps, like a joke.

This article was originally published in spectrum of science and has been reproduced with permission. It was translated from the original German version with the help of artificial intelligence and reviewed by our editors.