Whether you care about horoscopes or not, you probably know your zodiac sign. The 12 signs are based on the constellations as seen from Earth. Ancient astrologers used the stars to measure time and to try to tell the future. But because the Earth wobbles like a spinning top, our view of the stars has shifted by 1 degree every 72 years—meaning your sign may now be outdated. For example, someone born on November 24 is considered a Sagittarius because 2,000 years ago, that constellation was behind the sun on that date. But this year, the constellation behind the sun that day is Scorpio. Modern astrologers are aware of the mismatch but don’t see a problem with basing the signs on the stars as they used to be positioned. Although there’s no scientific basis to the idea that the stars influence our future, belief in astrology has endured for thousands of years, while other methods of fortune-telling have fallen out of favor. “Astrology is a shape-shifter,” says Dorian Greenbaum, a historian at the University of Wales Trinity Saint David. “Astrology goes along with whatever’s in vogue and manages to survive.”