By Claudine Zap

Fans of the Zodiac have been bombarded with the unsettling news that their astrological sign may not be what they thought.

The horror of switching from Gemini to Taurus had people rushing to the Web for answers, sending searches for "zodiac signs" into the stratosphere.

So has your sign changed? Probably not. But it all depends on what kind of astrology you follow. Let us explain.

It may come as a surprise that there are different branches of astrology. A main Eastern form, for example, called Sidereal astrology, looks to the background stars, those famous constellations, as its guide.

Western astrology -- which uses the zodiac -- has its signs fixed to the seasons. Most Westerners, and all those horoscope pages we eagerly check, go by the zodiac. These signs follow what early astrologers called star signs, whose reference points are the tropics that form a ring around the earth. The zodiac is based on our relationship to the sun, not the stars.

The back story: About 2,000 years ago, the astrological signs and the astronomical ones were the same. But not anymore. The locations of the signs are based on the sun's location on the first day of spring. That location in the sky has slowly drifted westward because of something called "precession" -- the earth continually wobbles (a scientific term for a slight motion) every 26,000 years. Since the constellations were first identified, they have shifted some 30 degrees. Translation: The signs have slipped about a month westward, relative to the stars.

What this means to you: If you follow astrology that is linked to the constellations, your sign would go from say, a Gemini to a Taurus. You could even have a 13th sign, Ophiuchus, which you may have read about.

"It's a huge point of confusion for the public," says Bing Quock, assistant director of Morrison Planetarium at the California Academy of Sciences. For those who follow Western astrology, "astrologers are not talking about the constellations at all. When an astrologer says the sun is in a certain sign, they're talking about the sign, the location relative to the equinox. They're not talking about the location of the constellations. "

In short, if you follow the Sidereal astrology, the Eastern branch, your sign may have shifted. (And most likely, no surprise to you at all: This news is hundreds of years old).