Why do modern scientists consider astrology to be a pseudoscience?

There are several approaches to this question, but the strongest argument seems to be based on an assessment of whether astrology uses scientific methods to improve its rate of success over time. There is no doubt that astrology has difficulty in making accurate and specific predictions. That, in itself, however, does not make it pseudoscientific. The problem is that astrology has not improved its power of explanation of events in over 2,000 years and, more importantly, practitioners of astrology:

• Make little attempt to develop the theory with the objective of improving the results.
• Have no interest in evaluating the theory in relation to other ideas.
• Are biased and selective in considering confirmations and disconfirmations of predicted results.

Science is a systematic way of developing new human knowledge about the natural world. Science is based upon a continual process of formulating, comparing and testing different theories. As new information is obtained, old theories are refined or replaced with new theories which have a better correlation to empirical observations and greater predictive power. It is the complete absence of, and even aversion to, any systematic attempt to improve its theoretical basis or its predictive results that makes astrology a pseudoscience.