Zodiac signs link the stars to your life, but not in the way you might think.

You wouldn't know it just by reading your horoscope, but the Zodiac constellations are impacted by the cosmically slow wobble of the Earth, known as precession.

That means the dates used to assign Zodiac signs by many Americans have become untethered from what actually appears in the sky.

"The cosmos is constantly in motion and changing and dynamic, and there is nothing fixed in theuniverse," said Melissa Rice, an associate professor of planetary science at Western Washington University.

That bit of trivia was recently highlighted by New York Times and Good Morning America. But those who study the stars say this is a fact long known by ancient astronomers, and the disconnect is essentially an intentional feature of the zodiac, not a bug.

In fact, there is another zodiac system that keeps the sun, stars and signs aligned, but it's more popular in India than in the Western world.

What is the Zodiac?

The Zodiac refers to the collection of constellations that emerge in the path that the sun appears to take through the sky from our perspective on Earth. More than 2,000 years ago, the Babylonians split that band of sky into twelve equal parts that correspond with twelve constellations.

Your Zodiac sign, or sun sign, is determined by the constellation that appears behind the sun on the day you were born.

Why the Zodiac signs don't align with the constellations

But the dates linked to our Zodiac signs don't perfectly align with the actual timing of their namesake constellation's appearance in the sun's path. There are several reasons why.

As the Earth travels through space, it is also wobbling like a top, a phenomenon called precession, Rice said. The planet's slow rotation, which takes about 26,000 years to complete, means that our view of the stars has shifted since the creation of the Zodiac.

"Precession doesn't change how the constellations appear in the sky, their shape or their order or their relationship to each other, but it changes when the sun appears to be in a different constellation at different times of the year," Rice said.

Though the Zodiac signs divide the calendar year into equal chunks, Rice said the constellations themselves aren't all the same size, which means the sun also spends less time behind some than others.

There is also a thirteenth constellation that appears in the sun's path that's been excluded from the Zodiac, though it's not entirely clear why, Rice said.

So, is my Zodiac sign wrong?

Ancient astronomers knew of these slow shifts in the night sky, according to Dorian Gieseler Greenbaum, who teaches cultural astronomy and astrology at the University of Wales Trinity Saint David. Still, Greenbaum said the Babylonians made a conscious choice to simplify the Zodiac and tie the twelve signs to the seasons so that Aries, for example, would be associated with the start of Spring.

That system, which is used by most Western astrologers, is known as the tropical Zodiac, Greenbaum said. Another form of astrology known as the sidereal Zodiac, which is predominantly used in India, does take precession into account.

"This doesn't mean that one is better than the other," said Greenbaum. "It's just two different ways of looking at the sky and time and its relationship to us on Earth."

'Two sides of the same coin'

The idea that our Zodiac signs are wrong because of precession has popped up many times in the past, those who study astrology say. A flurry of news articles about precession came out in 2011 after an astronomer mentioned the concept during an interview with The Minnesota Star Tribune, prompting several people to ask Dave Campbell, president of the American Federation of Astrologers, if their sign had really changed.

"It's like the 14th time I had to deal with this," said Campbell, owner of The Astrology Store in Glendale, Arizona.

Campbell said he's researched other branches of astrology, and though the tropical system resonates with him the most, he views both systems as valid.

"If you want to look at apples, look at apples," he said. "If you want to look at oranges, look at oranges. It's really not hard."

Campbell said he believes that conversation about precession resurfaces so often because some people are looking to debunk astrology. He said the latest round of debate has come amid a rise in interest in astrology since the pandemic, particularly among young people.

Nearly a third of U.S. adults consult astrology, tarot cards or fortune tellers at least once a year, though the portion of Americans who believe in astrology doesn't appear to have changed much in recent years, according to research from the Pew Research Center. A third of those say they do so to help make major decisions, and the rest do so just for fun.

Whether astrology "works" as a way to predict the future or not, modern astronomy would not be possible without the observations of ancient astrologers and the fields are "in some ways, two sides of the same coin," Greenbaum said.

"I don't think it's a science in the modern sense," she said. "I do think it's a science in the ancient sense, in that it is a system of knowledge that uses the sky as its knowledge base."

This article originally appeared on USA TODAY: Your Zodiac sign is the key to a fascinating cosmic quirk

Reporting by N'dea Yancey-Bragg, USA TODAY / USA TODAY

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