Pseudoscience (n.d.) is essentially, "any body of knowledge that purports to be scientific or to be supported by science but which fails to comply with the scientific method." Astrology (n.d), in general, is the belief that the position of celestial bodies in some way affect human activity and natural processes on Earth.
Image Source: http://www.astrology.com.tr
Believers in astrology typically use anecdotal evidence and/or false correlations as evidence of the reliability of their faith. As astrology claims to have causal effects on human behavior and circumstance, it is scientifically testable. And thus far, a number of tests have shown it to have no predictive power what-so-ever (Zarka, 2011). Even though astrology has been falsified scientifically, their practitioners continue to believe in it despite overwhelming evidence to the contrary.
Why it fails
There are a number of reasons why astrology just doesn't make the grade to be considered science. As you will see, almost all examples of evidence for astrology utilize some form of circular reasoning. See below:
• Astrology does not provide any mechanism(s) to explain how it would work even if it did. Astrology assumes ideas, concepts, processes, etc.. exist/work without there being any evidence of any causal relationships. In other words, astrology practitioners assume it works, and then make connections that may not even exist in reality.
• Astrology does not clearly explain how the stars affect human affairs. We are told to just accept that it does. Astrology does not identify a reasonable force known to current scientific disciplines which can account for any alleged changes in human behavior or alleged roles in human life experience.
• Astrology claims that somehow, the positions of the stars influence humans in some way. This would mean that a force/energy is somehow exerted as a result of these subjective visible patterns. No such force has been detected nor is there a reason to assume that such a force exists when human behavior can easily be explained by evolutionary psychologists, social scientists, and behaviorists.
• If astrology is true, we should be able to make predictions about human behavior and personalities. The evidence shows that there is no such correlation (Dean, et al, 2003); yet, the astrology practitioners still believe in its predictive[sic] power.
• Astrology practitioners claim that their horoscopes are accurate but when they are shown that they are not; they move the goal post disallowing an experimenter to experimentally test their claims.
• Astrology practitioners ignore any predictions that turn out to be false. This is recognized particularly when addressing astrologers and asking them to explain the fact that people with similar star signs can be dramatically different. There is no attempt at explaining these discrepancies in a manner that's scientific nor even rational.
All in all, astrology just isn't science. The 3 biggest flaws are that it has no predictive power, it cannot explain how the alleged causal mechanisms (stars and planets) influence human affairs, and it ignores more simple explanations for human behavior and human circumstance.
It is baffling to me how we have perfectly reasonable and sound explanations for a plethora of natural phenomena, yet pseudoscience still takes a foothold. The illusion of and the desire for control in our lives is something that all pseudo-scientific disciplines and paradigms feed upon. Science changes, updates, and modifies. Pseudoscientific beliefs remain unchanging, stagnant, and resistant to change over time. This provides an illusion of stability and certainty that is truly undeserved.
Astrology. (n.d.) Miriam-Webster Online Dictionary, Retrieved July 8th, 2016 from http://www.merriam-webster.com/dictionary/astrology
Dean G, Kelly I.W. (2003). "Is Astrology Relevant to Consciousness and Psi?". Journal of Consciousness Studies 10 (6-7): 175–198.
Pseudoscience. (n.d.). Wiktionary Online, Retrieved July 8th, 2016 from https://en.wiktionary.org/wiki/pseudoscience
Zarka, Philippe (2011). "Astronomy and astrology". Proceedings of the International Astronomical Union 5 (S260): 420–425.