Horoscopes and most astrology books list 12 zodiac signs, few people know that there are actually 13 signs. According to astronomers, Ophiuchus (November 30-December 17) is the one sign that has been ignored for thousands of years.

While Earth orbits around the sun, the sun appears in our sky in front of 13 groups of stars called constellations of the zodiac. People who were born during the time when the sun was in front of a certain constellation, get assigned their zodiac sign accordingly. Astrology books have identified 12 zodiac signs. But Ophiuchus, the 13th sign, was omitted.

“People might have known this for 4000 years," said Keith Waxman, an SF State astronomy teacher. “They may have ignored certain areas and divided the sky into 12 constellations and ignored Ophiuchus, even though they knew that the sun drifted through that area.”

The constellation’s borders have been established by astronomers since 1930, Waxman said. “There are really 13 regions of the sky. They are like states in the US," he explained. “The sign, which is Ophiuchus, really does exist in astronomy.”

But this is not all. The dates of the modern horoscopes and corresponding signs are off by about 21 days, astronomers say. This is because our planet wobbles around its axis and completes the loop in every 26,000 years. Every 78 years the Earth moves by a degree, which represents a day difference in the zodiac system.

“Each year the Earth is in a slightly different position in June,” said Waxman. This causes the sun to appear in front of a “slightly different amount of stars,” he added.

So why is this information not in astrology books and horoscopes? One answer is that modern astrology books still use an old system that the ancient Egyptians and Babylonians once used. But Waxman offers more explanations to the question of why the astrology information is not updated.

“Because it doesn’t matter,” said Waxman. He said he doesn’t believe that astrology dictates or predicts who you are. “If they add a new sign, people are going to be upset,” he added.

Another reason for omitting Ophiuchus is marketing, said Waxman. “If you change it all of a sudden, people might start buying less magazines, less horoscope booklets and people will lose money.”

Waxman, who believes in aliens and brings 4.5 billion-year-old meteorites to his class, breaks the news of 13 signs to his students every semester and receives mixed reactions.

“Most (students) think it’s funny,” he said. “Most are not that serious about their sign as far as letting it govern their life. But some are. Some people have had tears in their eyes when they read it.”

“I’m still me,” said Chris Colson, a 21-year-old psychology major who just found out that his real sign is Aries, not Taurus. But he wasn’t disturbed by the news because he doesn’t feel attached to his sign, he said.

Huckleberry Greenlee, 31, a SF State student enrolled in a masters program, thought she was a Scorprio. When she found out that her “real” sign is Virgo, she wasn’t bothered too much. “I think the whole system is pretty vague,” she said. “I don’t think it matters how you set it up with 12 or 13 signs.” But she did have plans on getting a Scorpio tattoo. These plans are now placed on hold, she said.

Check out how the new zodiac configuration affects the various signs.

Note: Dates may vary from source to source. For a slightly different perspective, along with a more detailed description of the 13th sign, visit www.starsandcoffee.com.