Ophiuchus is a real constellation, and the Sun does pass in front of it every year, roughly from the end of November to the middle of December. But it isn't a zodiac sign in Western astrology, because the tropical zodiac is twelve equal 30-degree sections tied to the seasons, not to the constellations. Your sign hasn't changed, and NASA never said it had.
The "13th sign" story resurfaces every few years, usually with a headline about NASA. Here's what's true about Ophiuchus, why the zodiac has twelve signs, and what it means if your birthday falls in Ophiuchus's stretch of the calendar.
The constellation behind the headlines
Ophiuchus, pronounced off-ee-YOO-kus, is Greek for "serpent bearer." It's a large, fairly faint constellation pictured as a man holding a snake, which forms its own constellation, Serpens. Serpens is split in two by Ophiuchus, a head on one side and a tail on the other, the only constellation divided that way.
The figure is usually identified with Asclepius, the healer of Greek myth, who learned medicine from the centaur Chiron. The serpent-wrapped rod of Asclepius is still a symbol of medicine today. Ptolemy included Ophiuchus among his 48 constellations in the second century, so it's anything but new.
What changed was the map. In 1930 the International Astronomical Union adopted official boundaries for all 88 constellations, drawn up by the Belgian astronomer Eugène Delporte. Those straight-edged borders put a slice of the Sun's yearly path inside Ophiuchus, between Scorpius and Sagittarius.
Why the zodiac has twelve signs, not thirteen
The zodiac of twelve equal signs was developed by Babylonian astronomers around 2,500 years ago, and later taken up by Greek astrologers. Twelve was a convenient number: twelve months, twelve equal slices of a circle, each 30 degrees.
As NASA's 2016 explainer put it, the Babylonians left the thirteenth constellation out so that the zodiac would match their 12-month calendar. The constellations were never all the same size, so the signs were always an idealized division of the sky, not a tracing of the star patterns.
In Western astrology, the link to the stars was dropped long ago. The tropical zodiac starts at the March equinox and divides the year by the seasons. Aries is the first 30 degrees after the equinox, whatever stars happen to sit behind the Sun. Ophiuchus has no place in that system, any more than a fifth season would.
What NASA actually said
In 2016, news sites picked up a NASA educational page for children that explained how the constellations behind the Sun have shifted since Babylonian times, and mentioned Ophiuchus. They turned that into "NASA changes the zodiac." NASA responded with a blog post that included a line widely quoted since: "So, we didn't change any zodiac signs. We just did the math."
The post made two points: that NASA studies astronomy, not astrology, and that Earth's slowly wobbling axis has shifted the constellations' positions relative to the calendar. That shift, called precession, is real and well understood. It's also the reason the sidereal zodiac used in Vedic astrology differs from the Western one by about 24 degrees. Our guide to sidereal vs tropical astrology explains it in full.
Signs vs constellations: the dates don't match anyway
Even if you wanted to follow the constellations, the familiar sign dates wouldn't survive. The constellations are wildly different sizes, so the Sun spends very different amounts of time in each. Approximate dates the Sun is in front of each constellation, using the IAU boundaries:
| Constellation | Sun passes through (approx.) |
|---|---|
| Capricornus | January 19 to February 16 |
| Aquarius | February 16 to March 11 |
| Pisces | March 11 to April 18 |
| Aries | April 18 to May 14 |
| Taurus | May 14 to June 21 |
| Gemini | June 21 to July 20 |
| Cancer | July 20 to August 10 |
| Leo | August 10 to September 16 |
| Virgo | September 16 to October 31 |
| Libra | October 31 to November 23 |
| Scorpius | November 23 to November 30 |
| Ophiuchus | November 30 to December 18 |
| Sagittarius | December 18 to January 19 |
The Sun spends about six weeks in Virgo and barely a week in Scorpius. A "constellation zodiac" would make Virgo a huge sign and Scorpio a tiny one, and would shift almost everyone's dates. That's a different system from either astrological zodiac, and no major astrological tradition uses it. The dates also drift by a day or so from year to year.
If you were born from late November to mid December
In Western astrology, you're a Sagittarius, and our Sagittarius traits page describes the sign. Sagittarius begins around November 22, so the whole Ophiuchus stretch falls inside it. If your birthday is near the Scorpio and Sagittarius boundary instead, check our Scorpio traits page too, and a free birth chart will give your Sun's exact degree.
In sidereal astrology, you're most likely a Scorpio, since the sidereal zodiac sits about 24 degrees behind the tropical one, but it's still a twelve-sign system with no Ophiuchus in it.
You'll find Ophiuchus "personality traits" online: healer, seeker, magnetic, secretive. They're modern inventions, often borrowing from the Asclepius myth, with no traditional astrological basis. If they appeal to you, enjoy them as a story. They won't change your chart. For the Asclepius connection told from the astrological side, see Chiron in astrology, named for his teacher.
Questions readers ask
What are the dates for Ophiuchus?
The Sun passes in front of the constellation Ophiuchus from about November 30 to December 18 under the modern IAU boundaries. That's an astronomical fact about the constellation, not a set of zodiac sign dates.
Did my zodiac sign change?
No. Western astrology uses the tropical zodiac, which is tied to the seasons and hasn't changed. The constellations behind the Sun have shifted over the centuries, which astrologers have known for a very long time; our explainer on what your sun sign is and isn't covers the history.
Is Ophiuchus used in Vedic astrology?
No. Vedic astrology uses a sidereal zodiac aligned to the stars, but it still divides the sky into twelve equal signs. Ophiuchus isn't one of them.
Why do some people say there are 13 signs?
Because the Sun crosses thirteen constellations under the modern boundaries, and the idea makes a good headline. A few writers have proposed thirteen-sign systems, but no established astrological tradition uses one.
