Are Astronomy, Astrophysics and Astrology All the Same?

The Jewelbox Cluster
Astronomy and astrophysics are the sciences that help us understand the workings of the stars and galaxies. European Southern Observatory

Astronomy and astrology are two subjects that people often get confused. The simplest way to think of them is that one is a science and the other is a parlor game. Astronomy covers both the science of stargazing and the physics of how stars and galaxies work (which is often referred to as astrophysics). Astronomy and astrophysics are often used interchangeably, although there are some differences between them when we get down to the details. 

The third term, astrology, is an ancient method where soothsayers would use the stars to tell fortunes. The early practitioners would watch the stars and planets but had no scientific knowledge about them. They simply used them as a tool for selling predictions about people's lives. Astrology is mistakenly used by many people to refer to astronomy, but there's no scientific basis in the current practice of astrology. However, the work of the ancient astrologers did form the basis for the star and navigational charts used by the ancients, and some of the constellations we know today.

IAU chart for Pisces constellation.
The IAU constellation designation for Pisces includes the main pattern plus numerous other stars. The early astrologers used the green outline of the stars as a way to divide the sky up into "houses", through which the planets would wander. Pisces is a Zodiac constellation, meaning a region of the sky that the Sun and planets appear to wander through. To astrologers, where a planet or the Sun was on the day of a person's birth had some meaning. But, today, there is NO measurable link between those objects and the person being born. IAU/Sky & Telescope 

Astronomy and Astrophysics

The difference between "astronomy" (literally "law of the stars" in Greek) and "astrophysics" (derived from the words Greek words for "star" and "physics") comes from what the two disciplines are trying to accomplish. In both cases, the goal is to understand how objects in the universe function. 

Astronomy describes the motions and origins of the heavenly bodies (stars, planets, galaxies, etc.). It also refers to the subject that you study when you want to learn about those objects and become an astronomer. Astronomers study the light emanating or reflected from distant objects

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in astronomy, the bright star Alpha Centauri and its surrounding stars are studied by both astronomers and in astrophysics in order to understand their characteristics. . This is a main sequence star, just as the Sun is. NASA/DSS

Astrophysics is literally the physics of the many different types of stars, galaxies, and nebulae. It applies the principles of physics to describe the processes involved in the creation of the stars and galaxies, as well as learning what drives their evolutionary changes. Astronomy and astrophysics are definitely interrelated but are clearly trying to answer different questions about the objects they study. Think of astronomy as saying, "Here's what all these objects are" and astrophysics as describing "here's how all these objects work." 

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Astrophysics tells scientists about how stars, such as the Sun, work. Astrophysicists may also study how the solar wind interacts with the planets, as shown here. NASA's Goddard Space Flight Center

Despite their differences, the two terms have become somewhat synonymous in recent years. Most astronomers receive the same training as astrophysicists, including the completion of a graduate program in physics (although there are many very good pure astronomy programs being offered). Others begin in mathematics and gravitate to astrophysics in graduate school.

Much of the work done in the field of astronomy requires the application of astrophysical principles and theories. So while there are differences in definitions of the two terms, in application it is difficult to distinguish between them. When someone studies astronomy in high school or college, they first learn purely astronomy topics: motions of celestial objects, their distances, and their classifications. A deeper study of how they work requires physics and eventually astrophysics.

Astrology

Astrology (literally "star study" in Greek) is largely regarded as a pseudoscience. It does not study the physical characteristics of stars, planets, and galaxies. It is not concerned with applying principles of physics to the objects it uses, and it has no physical laws that help explain its findings. In fact, there's very little "science" in astrology. Its practitioners, called astrologers, simply use the positions of stars and planets and the Sun, as seen from Earth, to predict people’s individual characteristics, affairs and future. It's largely akin to fortune-telling, but with a scientific "gloss" to give it some kind of legitimacy. In truth, there's no way to use stars and planets to tell anything about a give person's life or loves. It's all very imaginary and fanciful, but some people do derive a lot of satisfaction from fiddling with it.

The Ancient Role Astrology Played in Astronomy

While astrology has no scientific basis, it did play a preliminary role in the development of astronomy. This is because early astrologers were also systematic stargazers who charted the positions and motions of celestial objects. Those charts and motions are of great interest when it comes to understanding how stars and planets move through space.

Astrology diverges from astronomy when astrologers attempt to use their knowledge of the sky to "predict" future happenings in people's lives. In ancient times, they did this mostly for political and religious reasons. If an astrologer could predict some wonderful thing for his or her patron or king or queen, they might get to eat again. Or get a nice house. Or score some gold. 

Astrology diverged from astronomy as a scientific practice during the years of the Enlightenment in the Eighteenth Century, when scientific studies became more rigorous. It became clear to scientists of that time (and ever since then) that no physical forces could be measured emanating from stars or planets that could account for the claims of astrology.

In other words, the position of the Sun, Moon and planets at a person's birth have no effect on that person's future or personality. In fact, the effect of the doctor assisting with the birth is stronger than any distant planet or star. 

Most people today know that astrology is little more than a parlor game. Except for astrologers who make money off of their "art", educated people know that the so-called mystical effects of astrology have no actual scientific basis, and have never been detected by astronomers and astrophysicists.

 Key Takeaways

  • Astronomy is the scientific study of the stars, planets, and galaxies, and their motions.
  • Astrophysics uses principles and laws of physics to explain HOW stars, planets, and galaxies work, and how they formed.
  • Astrology is not a scientific study of anything. It is an amusement that uses star constellations and planet positions to somehow explain someone's life, loves, and personality. There's no known way to use stars and planets to do this.