The Babylonians were lazy: When they came up with the zodiac signs, they left one out on purpose. Using 12 signs instead of 13 was more convenient because it fit their calendar of 12 lunar cycles per year. But that means everyone who’s adopted their astrological calendar and associated personality profiles in the millennia since have been wrong.

NASA pointed out the error last month and offered up a correction. The new zodiac calendar has some big changes. Not only are there now 13 signs, the dates have changed in some cases. NASA updated the calendar to reflect the actual amount of time the sun spends aligned with each constellation, which has changed since the Babylonian’s time thanks to the Earth’s tilt. Scorpio, for example, only takes up seven days of the year. The new sign, Ophiuchus, takes up 19 days.

The new zodiac, complete with Ophiuchus

For most people, zodiac signs will shift to the sign previous. Many Scorpios are now a Libra, for instance. For a few people, signs won’t change at all; if you were born between March 11 and 20, for example, you’re still a Pisces. You can use this handy tool to find your new sign.

Here’s the new calendar:

Capricorn: January 20 - February 16

Aquarius: February 16 - March 11

Pisces: March 11 - April 18

Aries: April 18 - May 13

Taurus: May 13 - June 21

Gemini: June 21- July 20

Cancer: July 20 - August 10

Leo: August 10 - September 16

Virgo: September 16 - October 30

Libra: October 30 - November 23

Scorpio: November 23 - 29

Ophiuchus: November 29 - December 17

Sagittarius: December 17 - January 20

NASA, despite their calculations and calendar update, was quick to point out that astrology is, in fact, not a science. Astronomy, on the other hand — the study of stars and space — is a science. Astrologists contend that the slight gravitational pull of the sun and stars can affect personalities depending on the time of year and when people were born. Astronomers see no such personality/stellar correlation.

Photos via NASA, The British Library

Kelsey Kennedy is a science journalist from Oregon, now based in New York City. She's written about science, technology, and the environment for Quartz, Undark, and Scienceline.