I believe the fundamental dividing line between astronomy and astrology lies in the objective reality of the material world. The objective reality of the material world is a very basic philosophical concept. It explains that the material world exists independently of human thoughts, wishes, and subjective interpretations, and that its laws are stable and universal and do not change according to human will. For a view to become “scientific,” it must be based on the objective reality of the material world and must satisfy the following conditions. First, it describes phenomena of the material world that exist independently of human consciousness. Second, it must be falsifiable: there must be observable material facts that could prove the view wrong. Third, it must be possible to test it repeatedly through observation and measurement of material objects and processes, so that different researchers can reach consistent results. Fourth, it must have a material mechanism, and cannot rely only on subjective association, symbolic analogy, or belief. Finally, it must be revisable: if objective material evidence contradicts the view, the view must be modified or abandoned, and it cannot be saved by inventing extra reasons at the last minute.

Returning to our question, why is astronomy a science while astrology is not? Astronomy studies real material celestial bodies: stars, planets, and galaxies. These entities objectively exist in the material universe. Astronomers observe material phenomena, propose testable predictions, and verify or refute hypotheses through measurement and observation. When new objective evidence conflicts with an existing theory, the theory is revised or even abandoned. Its claims describe the real laws of motion of matter in the universe. Astrology, however, claims that the positions of stars determine a person’s character and fate. This claim cannot be built on the objective reality of the material world. There is no confirmed physical mechanism by which distant celestial bodies could influence an individual person’s life. It also cannot be reliably falsified: when a prediction fails, astrologers can always find extra excuses instead of abandoning the core claim. Finally, and most importantly, its descriptions are not measurable material interactions.

From the perspective of critical rationalism, we can never test all cases, but as long as we find one counterexample, we can refute a theory. Therefore, the boundary between science and pseudoscience is defined as “falsifiability.” That is, what we call science always has the possibility of being proven wrong. For example, with the development of astronomical technology, the geocentric theory was eventually overturned, but it was still a falsified scientific theory, not pseudoscience. The most fatal problem with astrology, fortune-telling, and similar practices is that we cannot prove them wrong, because the power of interpretation lies entirely with the fortune-teller, who can use ambiguous answers to ensure that he or she is always “correct.” Astronomy is different: if observations deviate further and further from the theory, the theory can be proven wrong. Popper gives a rigorous and full explanation of this topic in Conjectures and Refutations.

Astronomy uses mathematical models, makes precise and falsifiable predictions, accepts peer review, and corrects itself when it is wrong. Astrology, by contrast, only makes vague and fake predictions, completely lacks a physical mechanism, has made no progress in 2,000 years, and relies on superstition and mysticism. Its structure makes it impossible to test accurately.

Astronomy relies on measurable evidence, repeated observation, and testable predictions. Astrology’s claims are more mystical and vague and cannot be falsified. A scientific idea needs solid evidence, must be open to testing, and must be revisable when new evidence contradicts it.

No viewpoint can prove astrology is false, and no viewpoint can prove it is true either. It is just that more or fewer people are willing to believe it.

Astronomy earns trust through reliable predictions, careful testing, and correction of errors; astrology has not shown comparable success. Although the boundaries of science are debated, scientific claims are to be considered accountable to evidence.

Well, to answer this question, we need to know what science is first. Some scientists define science as both a body of knowledge and a process (https://undsci.berkeley.edu/). If so, then astrology can also be counted as a part of science. It has its own rules, and it has outcomes that can somehow be believed to be true. It matches every process that a science requires. But if we consider science as something that can be explained from the perspective of physics (biology, chemistry, and astronomy all involve a lot of physics), then astrology may fall outside the definition of science.