why wasnt ophiuchus added into the zodiac?

Answer 1

The division of the ecliptic into twelve equal "houses" or "signs" is a tradition that goes back many centuries. It is based on further division of the natural division of the year into four by the equinoxes and solstices. Twelve is also the approximate number of lunar months in a year.

The twelve signs of the zodiac persist today by way of traditional mythology, and also astrology. The old mythology is what it is, and the astrologers will stick with the number twelve because, as mentioned, it divides the sky evenly. Ophiuchus became a member of the ecliptic when the International Astronomical Union (IAU) published an official division of the sky into 88 constellations around 1930. Its space on the ecliptic formerly belonged to Sagittarius and Scorpius.

In any case, the astrological zodiac (in western astrology, at least) is based on the seasons, not the constellations. The signs and constellations lined up back in the second century, when Claudius Ptolemy wrote his books on astrology and astronomy, but they are now offset by around twenty degrees.

Answer 2

The "zodiac" is defined as the 12 constellations which the sun appears to move through during the course of the year. The sun doesn't really appear move through the figure of Ophiuchus, so, while it is a perfectly good constellation, it isn't part of the zodiac.

If you are following the modern constellation boundaries, it DOES appear that the sun crosses part of the territory assigned to Ophiuchus, but while this dark spot between Scorpio and Sagittarius is defined by modern astronomers as belonging to Ophiuchus now, back in the ancient times when the zodiac was invented, it was simply dark sky that defined the border between Scorpio and Sagittarius.

As others have pointed out, they wanted to split the zodiac into 12 constellations with the sun spending 1 month in each constellation. Ophiuchus simply didn't appear close enough to the line of the zodiac to make the cut.

Answer 3

In astrology the zodiac is the 12 houses, each of which is exactly 1/12 of a circle, or 30 degrees, of the ecliptic. Each house is named after the nearest constellation, but the houses do not correspond exactly to the constellations. Especially, precession has moved the houses over about a constellation and a half from where they were thousands of years ago.

Answer 4

Already had twelve symbols and they are evenly spread across the night northern sky.