Horoscope fans fear they may have been following the wrong guidance all their lives.
Ophiuchans are said to be clever, flamboyant but power-hungry.
Naomi Rowan, 22, said: "I couldn't sleep and found out that my star-sign has apparently changed and instead of a Sagittarius I am now an Ophiuchus! I'm not sure what the traits are, but perhaps it will make more sense to me than Sagittarius ever did."
The realignment has affected other star signs.
Mandy Southgate, from Kent in the UK, said: "No way I'm an Aries. Taurus forever. I'm going to ignore Ophiuchus just like I ignored Pluto not being a planet."
"So I am no longer a Sagittarius, I'm now an Ophiuchus. Took me years to learn how to spell Sagittarius now have to learn how to spell and pronounce Ophiuchus," joked Shaun Connolly, a digital media apprentice from Scotland.
Ophiuchus was originally spotted by the ancient Babylonians, about three millennia ago.
"Even according to the Babylonians' own ancient stories, there were 13 constellations in the zodiac," Nasa said.
"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.
"So the Babylonians picked one, Ophiuchus, to leave out.
"Then they assigned each of those 12 constellations equal amounts of time."
But experts say that the Earth's wobbly orbit means it is no longer aligned to the stars in the same way as when the signs of the zodiac were first conceived and now Ophiuchus is even more prevalent in the sky.
"Now, 3000 years later, the sky has shifted because Earth's axis (North Pole) doesn't point in quite the same direction," Nasa said.
It has been pointed out that the sun aligns with Ophiuchus for 18 days between November 29 and December 17. It is only aligned with Scorpio, beforehand, for seven days.
This means the whole zodiac system would change, with Ophiuchus nestling between Scorpio and Sagittarius.
While it's not the first time the idea of Ophiuchus as a 13th Zodiac sign has come to light, some astrologists are keen to stick to the status quo.
A self-styled "consultant to the stars", Sally Kirkman, from Blackpool told The Daily Telegraph: "No one is going to have Ophiuchus as their star sign, it means nothing. All the star signs remain as they have since ancient times.
"In brief, western astrology, which is the standard in many countries in the world, is based on the tropical zodiac. The 12 star signs of the zodiac are fixed and they connect to the Equinoxes and Solstice dates which are the same year in, year out and are linked to the seasons. They do not change - the dates of each star sign remain the same.
"There is a beautiful symmetry in the 12 signs of the zodiac which ancients knew about and their hidden knowledge has been passed down throughout time.
"You won't find any accredited astrologer telling you that Ophiuchus is a star sign. Anyone who does tell you that it is a new star sign doesn't understand their craft."
Romina Russell, a Los Angeles based author who has written four science fiction novels inspired by astrological signs says that the traits of Ophiuchans of old are reflected in people born under that star sign today.
"According to legend, the Serpent Bearer constellation had two planets - one covered in fiery molten lava and the other consisting of a large swamp," she said.
"Ophiuchans built their short-lived civilisation on the marshy world, where they slept in huts and spent most of their time exploring the wilderness and developing remedies for ailments, which they exported to all the Houses.
"House Ophiuchus represented Unity. Its people were spirited, magnetic, impulsive, clever, flamboyant and at times jealous, power-hungry and temperamental. At their hearts, they were healers who hoped to one day rid the Zodiac of every ill, disease, violence, and bring everyone closer together.
"Ophiuchans had a natural affinity for snakes, and there was a special species of serpent, the Zawinder, with whom their House's Zodai developed a psychic connection. Each Zodai would capture and adopt his own Zawinder, which they would then use to spread messages to others in the swamp.
"House Ophiuchus had the greatest diversity in the Zodiac—people's skin, hair, and eye color spanned the full range of the spectrum. Yet, upon entering their teens, Ophiuchans developed scaly skin that would protect them from various creatures' bites and the natural elements."
