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Any websites or books that refer to Ophiuchus as the 13th zodiac sign are anything but reliable. The zodiac is a mathematical division of the ecliptic into 12 equal partitions of 30 degrees. There never has been and never will be a 13th sign of the zodiac since that would be a mathematical impossibility.

Modern day astronomers often perpetuate this hoax in the hope of undermining the astrological reliance upon the zodiac. But all they really do is reveal their own ignorance of a tool invented by the ancient forebears of their own study.

I trust you understand the difference between the astrological signs of the zodiac and the constellations of stars in the sky which once roughly approximately to the location of the signs and in whose honour the zodiac signs are named. These are 12 of the main constellations close to the ecliptic. Ophiuchus is another constellation close to the ecliptic but it wasn?t included in the list of twelve after whom the zodiac signs were named. This doesn?t give it any special significance because the zodiac signs are used differently to the way we use the constellations.

The Fixed Stars website gives a good overview of the history of the symbolism attached to constellation Ophiuchus at http://www.winshop.com.au/annew/Ophiuchus.html

For a history of the development of the zodiac as a tool that superseded the constellations for astronomical measurement and symbolic meaning see Heavenly Imprints on this site at http://www.skyscript.co.uk/zodiachistory_print.html