COMPUTERJI, yeh jawab galat hai. In a Kaun Banega Crorepati show, a woman was asked how many signs of zodiac were there. "Twelve" was the answer she chose and, after due ceremony, computerji declared her correct.

This answer, as a matter of fact, is wrong. There are actually 13 zodiac constellations. The 13th sign, Ophiuchus, is sandwiched between Scorpio and Sagittarius and its existence was officially acknowledged by the Royal Astronomical Society in 1995.

Not only is the total count of zodiacal signs at variance with common beliefs, the actual dates and the number of days the sun spends in each of them also differ from what astrologers would have us believe. About 86 per cent of the world’s population has its ‘birth signs’ wrong.

Zodiac is a belt in space extending nine degrees on either side of the plane of the Earth’s orbit, also known as the ecliptic. The ancient Greeks, in 600 BC, saw the stellar formations and found it easier to keep track of them if they were given animal names. The zone through which the ecliptic passes was called zodiakos kyklos or the circle of animals. They could count only 12 of them and divided the entire orbit into equal 30 degree segments. Each period of zodiac, or ‘birth sign’, was so called because at the time of a person’s birth, the sun, as seen from the Earth, was placed in front of that particular constellation.

However, the calendar months corresponding to the position of the constellations 2600 years ago have changed. This has happened because there is a wobble in the earth’s spin, like that of a top slowing down, arising out of the pull of the sun and the moon on our planet’s equatorial bulge. This ‘precession’ causes the dates of the zodiac calendar to slip about one day every 70 years.

Two and a half millenniums ago on March 21 the sun would have just entered the stellar grouping of Aries, the ram. Today it sits in Pisces on that date. In 1998, John Mosley of the Griffith Observatory wrote, "Originally the sun was in front of the stars of Gemini during the first two weeks of May. Now it is in front of the stars of Taurus during the same two weeks.

"The sun used to enter Cancer during summer solstice (hence the term Tropic of Cancer for the latitude where the sun is overhead on that date). This year it is in Gemini. Beginning in 1990, the sun will be in Taurus at the summer solstice, two constellations off its ‘original’ position."

Even before Christ was born, Greek astronomers had discovered the Earth’s wobble and knew they had a problem on their hands. The sun was supposed to be in Aries when spring began, but was actually found to be in front of the stars of Pisces. "The astrologers," says Mosley, "took this bombshell in their stride and declared that the signs drifted with the sun."

Astrologers still consider a person born in the first two weeks of May a Taurus. Astronomers concede that may have been true if you were born 2600 years ago, but today that would make you an Aries. Most Librans are now really Virgos. Mosley calculates, "Of the 366 possible birth dates, the astrological sign is off by one constellation for 84 per cent and by two constellations for 2 per cent of the people."

Not only have the dates shifted, they are not anywhere as equal as the fortune-tellers would have us believe. The zodiac belt is not divided neatly into 30 degree sections. David Hasenauer, writing in the magazine Sky and Telescope in 1998, estimated that Virgo had a 45-day spread, whereas Scorpius has only six. The location and the time span of each constellation has been mapped meticulously, like a surveyor delineates irregular parcels of land, taking coordinates from different points in all directions.

It was while they were doing this exercise that astronomers confirmed the presence of a 13th constellation. Suspicions about its existence arose first in the mind of Austrian astronomer Rudolf Spitaler in 1890. For half a century thereafter the discovery received little attention, but some sort of investigation did start in the 1930s. In the 1990s, three astronomers in different locations in the USA, in coordination with each other, did some intensive research on the subject. Soon several others in the fraternity joined in and the discovery of a "globular cluster on the far side of the Milky Way’s centre" was announced.

The new discovery has been given the name "Ophiuchus" whose icon is the ‘serpent bearer’. It appears between November 30 and December 17, which means that half the Sagittarians are actually Ophiuchis!

Astronomers will never stop gaining more knowledge of the universe, and never claim that any discovery is ‘final’, but astrologers have a different attitude. They will be loath to admit that zodiac formations have changed over the centuries and that what they are peddling today is 86 per cent false.