Astronomers say zodiac signs are out of date due to Earth's wobble
Axial precession has moved the backdrop of the stars over millennia, meaning the sun’s position on birthdays no longer lines up with the traditional 12 signs, scientists say.
Astronomers say the traditional 12-sign zodiac is out of date by more than 2,000 years because of the Earth's axial precession, a slow wobble that shifts the backdrop of the stars over time. The Sun's position relative to distant star patterns has drifted since the Babylonians first codified the zodiac, meaning many people’s sun signs no longer match the constellations that share their names.
Axial precession is a roughly 26,000-year cycle in which the planet's axis traces a slow circle in space. The wobble arises because Earth is not a perfect sphere and has a bulge around the equator. The Sun and Moon's gravity tug on that bulge, causing the planet to wobble like a spinning top that is gradually losing speed. As a result, the same calendar dates now align with different portions of the sky than they did when the system was created more than two millennia ago. For most people, the zodiac has effectively shifted by one sign from what they were taught, astronomers say. While astrology and astronomy once shared common ground, they moved apart during the Scientific Revolution, and by the 1800s they were generally treated as separate disciplines.
"Think of Earth like a spinning top that's starting to slow down," said Dr. Mark Thompson, an astronomer, science broadcaster and author. "Earth's axis traces out a big, slow circle in space, taking about 26,000 years to complete the loop. This happens because Earth isn't a perfect ball; it's a bit fatter around the middle. The Sun and Moon's gravity tug on that bulge, causing the whole planet to wobble like a wonky spinning top." With that wobble, the stars behind the Sun on any given date shift, so the Sun sits in a different background constellation now than it did 2,500 years ago. When people ask what sign they are, astronomers explain that the astronomical backdrop has moved even if the calendar hasn’t.
But the two fields diverged long ago in method and emphasis. Astronomy studies the physical positions of stars and planets, while astrology’s traditional sun signs are tied to the seasons and, according to some practitioners, to energies that do not correspond to the stars themselves. Dr Thompson noted that at times the two discussions have different aims: facts about celestial positions versus readings that purport to describe personality or fate based on those positions. He added that while astronomers acknowledge the drift, many astrologers continue to frame signs around seasonal, rather than stellar, logic.
Two factors amplify the divide. First, constellations vary greatly in size in the sky, so the Sun does not spend equal amounts of time in each one. Virgo can sweep across the sky for weeks, while tiny Scorpius is traversed in far fewer days. The opposite result is a calendar that looks neat on paper but does not reflect the real geometry of the sky. Dr. Sheila Kanani, a planetary scientist and author of The Starspotter's Guide, notes that the ancient practice of drawing 12 equal slices of the sky ignored these unequal stretches. "The Sun spends weeks drifting through sprawling Virgo, but barely a week in tiny Scorpius," she said, explaining why the original scheme did not map cleanly to reality.
A second factor is the presence of Ophiuchus, sometimes described as the 13th constellation. The Sun spends about 18 days moving through Ophiuchus each year, and some modern astrologers have tried to incorporate it into a new set of signs. Most, however, opt to exclude it and keep 12 signs, arguing that Western horoscopes are season-based rather than strictly star-based. If the dates were updated to include Ophiuchus, some born between late November and mid-December might shift from Sagittarius to what some call an Ophiuchian sign, or from Scorpio to Ophiuchus-adjacent results. Dr. Kanani said, "If we updated the zodiac, I would actually shift from being Sagittarian to being Ophiuchian. All of this shows just how fluid and fascinating our view of the sky really is."
The scientific consensus remains that there is little evidence of a reliable link between when someone is born and their personality or life events. Dr. Thompson emphasized that even if the astronomical backdrop has moved, that does not validate astrology’s claims. "Study after study has failed to find any real connection between when you're born and your personality or life events," he said, adding that the gravitational pull from the doctor or nurse delivering you likely has more influence than Jupiter does. The upshot, according to scientists, is that readers should treat horoscopes as entertainment rather than guidance grounded in celestial mechanics.
The public debate over zodiac signs has been amplified by media coverage in recent weeks. The New York Times reported on the updated astronomical perspective, prompting a flurry of responses from astrologers on social media. One prominent astrologer, Aliza Kelly, argued that modern tropical astrology remains anchored to the seasons rather than the actual positions of constellations. "Modern tropical astrology is not based on the stars but the seasons," she said, highlighting that astrology has long maintained a geocentric framework focused on human experience rather than stellar geometry. Thompson cautioned that such explanations can confuse the public about what science actually supports, noting that while astrology has cultural and historical significance for many people, it does not reflect the physics of celestial motion.
For readers, the core message is simple: the sky as observed today does not align perfectly with the conventional zodiac signs used in everyday horoscopes, a result of a slow, inexorable astronomical process. This disparity underscores the difference between astronomical fact and astrological interpretation. While many people enjoy reading about star signs and their supposed personality traits, scientists urge caution against treating horoscopes as predictive science. The planet’s cycles and the mathematics of precession are real, measurable phenomena, but their relevance to human affairs remains outside the scope of empirical evidence. In the end, the sky continues to move, and so too do the meanings attached to the signs we have known for centuries.