How did astrology come into existence? Why do people believe in it so much?How did it come into existence?
Astrology is science of probability and statistics.
Our ancestors were intelligent people. They could predict movement of planets, eclipses, transitions, retrogrades quite precisely. Every branch of science rely heavily on observations. The early astronomers did observations and figured out the math and patterns behind the movement of celestial bodies.
If you look closely, the Indian astrology is also science of psychology. Over the years of research the ancient sages found patterns in human behavior. If we do that now, the obvious question would appear in our mind that what could govern behavior of a person? Does the time when s/he is born have any relation with the way s/he will behave? Is it set of chemicals? Is it geographical conditions?
Now if one wants to predict it, one needs to correlate the patterns with something. After correlating, there comes observation part, observing if at all there is correlation between those two seemingly separate events. (err Butterfly effect? ) After finding reasonable relation between the patterns over years and generations of observation one can safely form a complete branch of studies over it.