Every year or two a headline announces that the zodiac has a thirteenth sign, Ophiuchus, and that your sign has changed. It hasn't. Here is what is actually going on.
Signs are not constellations
Western astrology uses the tropical zodiac: twelve equal 30° segments that start at the spring equinox. They borrowed their names from constellations about 2,000 years ago, but the signs are measured from the seasons, not from the stars. Constellations are uneven shapes — Virgo is huge, Scorpius is small — and the Sun's path crosses thirteen of them, including Ophiuchus, the Serpent Bearer.
Why the dates drift
Earth's axis wobbles like a spinning top, a cycle called precession that takes about 26,000 years. That slowly slides the star backdrop against the equinoxes. Today, on your birthday, the Sun usually sits in front of the constellation before the one your sign is named after. Astrologers have known this since antiquity; the tropical zodiac was designed to follow the seasons regardless.
Where the story came from
In 2016 a NASA children's page explained precession and mentioned Ophiuchus. It was reported as "NASA changed the zodiac", went viral, and has resurfaced ever since. NASA was explaining astronomy, not revising astrology.
So what's my sign?
Exactly what it was. If you were born between November 29 and December 17, you are a Sagittarius in the tropical zodiac. Look up the sign for any birthday or read about the Sagittarius personality.
Common questions
Is Ophiuchus a real zodiac sign?
Ophiuchus is a real constellation the Sun passes in front of from roughly November 29 to December 17. It is not one of the twelve signs of Western astrology, which are equal 30° slices of the sky tied to the seasons.
Did NASA change the zodiac signs?
No. In 2016 a NASA education page explained that the constellations don't line up with the signs. Headlines turned that into 'NASA changed your sign'. NASA does not do astrology and changed nothing.
Why don't the dates match the constellations?
Earth's axis wobbles slowly (precession), shifting the backdrop by about one degree every 72 years. The tropical zodiac is fixed to the equinoxes, not to the stars, so it was always meant to drift away from the constellations.
What if I was born November 29 – December 17?
In the tropical zodiac used on this site you are a Sagittarius. Sidereal astrology (used in Vedic tradition) shifts signs by about 24 days but still uses twelve signs, not thirteen.