Read
...this is where i started
The Zodiac Conspiracy: Your Real Sun Sign
Dr. Atara
Indiana: Xilbris Corporation (2011)
Page 13, 14
“...During those early years astronomy and astrology were equals and both were considered science. These scientists believed that whatever constellation the sun was "in" when you were born helped shape your identify. They were aware of the fact that there are 13 constellations and that the sun travels thru each of them and all of them should be recognized. However, Greek astrologers/scientists, especially Ptolemy created a new paradigm of astrology called the tropical zodiac and decided that including the 13th constellation in their calculations would be too complicated.
This simplistic paradigm was designed to be shared with less educated people who might not understand the complicated configurations of science and math. Their paradigm was 12 signs, 30 degrees for each sign, which makes a 360-degree chart wheel. Thirteen would be awkward in that tidy little equation. By omitting the 13th constellation and silencing sidereal astrology, the vast majority of people could remain ignorant regarding the link between astrology and astronomy.
The conspiracy of silence also destroyed any links between Egypt and astrology. Ptolemy's paradigm made Greek mythology and astrology the most dynamic originators of this ancient scientific art..."
and then advanced here:
what about sidereal?
... please make yourself at home ... 