Yes, you may be reading the wrong horoscope. No, it isn't NASA's fault your zodiac sign changed.

(Image credit: Eva Hambach/AFP/Getty Images)

published 16 July 2020

There are actually 13 signs of the zodiac, and the Earth's axis has shifted since the Babylonians codified the horoscope dates some 3,000 years ago, so if you are a believer in astrology but also scrupulously exact about your science, you may have to change which star sign you were born under.

NASA wrote about the the 13th zodiac sign, Ophiuchus, four years ago, and it also noted that other traditions recognized up to 24 zodiac constellations — so, options — but the information has been in the public domain for at least 20 years. Why does it pop up again every few years? Maybe it's something in the stars. But whatever the reason, it's always new knowledge to someone, so here is NASA's explanation:

When the Babylonians first invented the 12 signs of zodiac, a birthday between about July 23 and Aug. 22 meant being born under the constellation Leo. Now, 3,000 years later, the sky has shifted because Earth's axis (North Pole) doesn't point in quite the same direction.Now Mimi's Aug. 4 birthday would mean she was born "under the sign" of Cancer (one constellation "earlier"), not Leo.The constellations are different sizes and shapes, so the Sun spends different lengths of time lined up with each one. The line from Earth through the Sun points to Virgo for 45 days, but it points to Scorpius for only 7 days. To make a tidy match with their 12-month calendar, the Babylonians ignored the fact that the Sun actually moves through 13 constellations, not 12. Then they assigned each of those 12 constellations equal amounts of time. Besides the 12 familiar constellations of the zodiac, the Sun is also aligned with Ophiuchus for about 18 days each year. [NASA]

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Peter has worked as a news and culture writer and editor at The Week since the site's launch in 2008. He covers politics, world affairs, religion and cultural currents. His journalism career began as a copy editor at a financial newswire and has included editorial positions at The New York Times Magazine, Facts on File, and Oregon State University.