Topic 7 – Astronomy vs Astrology

It’s important to realize that science is not the only valid way of seeking knowledge. For example, suppose you are shopping for a car, learning to play drums, or pondering the meaning of life. In each case, you might make observations, exercise logic, and test hypotheses. Yet these pursuits clearly are not science, because they are not directed at developing testable explanations for observed natural phenomena. As long as nonscientific
searches for knowledge make no claims about how the natural world works, they do not conflict with science.

However, you will often hear claims about the natural world that seem to be based on observational evidence but do not treat evidence in a truly scientific way. Such claims
are often called pseudoscience, which means “false science.” To distinguish real science from pseudoscience, a good first step is to check whether a particular claim exhibits all three hallmarks of science. Consider the example of people who claim a psychic ability to “see” the future and use it to make specific, testable predictions. In this sense, “seeing” the future sounds scientific, since we can test it. However, numerous studies have tested the predictions of “seers” and have found that their predictions come true no more often than would be expected by pure chance. If the “seers” were scientific, they would admit that this evidence undercuts their claim of psychic abilities. Instead, they generally make excuses, such as saying that the predictions didn’t come true because of “psychic interference.” Making testable claims but then ignoring the results of the tests marks the claimed ability to see the future as pseudoscience.

How is astrology different from astronomy?
The basic tenet of astrology is that the apparent positions of the Sun, Moon, and planets among the stars in our sky influence human events. The origins of this idea are easy to understand. After all, the position of the Sun in the sky certainly influences our lives, since it determines the seasons and the times of daylight and darkness, and the Moon’s position determines the tides. Because planets alsomove among the stars, it probably seemed natural to imagine that they might also influence our lives, even if the influences were more subtle.

Ancient astrologers hoped to learn how the positions of the Sun, Moon, and planets influence our lives by charting the skies and seeking correlations with events on Earth. For example, if an earthquake occurred when Saturn was entering the constellation Leo, might Saturn’s position have been the cause of the earthquake? If the king became ill when Mars appeared in the constellation Gemini and the first-quarter moon appeared in Scorpio, might another tragedy be in store for the king when this particular alignment of the Moon and Mars next recurred? Surely, the ancient astrologers thought, the patterns of influence would eventually become clear, and they would then be able to forecast human events with the same reliability with which astronomical observations of the Sun could be used to forecast the coming of spring. Because forecasts of the seasons and forecasts of human events were imagined to be closely related, astrologers and astronomers usually were one and the same in the ancient world. For example, in addition to his books on astronomy, Ptolemy published a treatise on astrology called Tetrabiblios, which remains the foundation for much of astrology today. Interestingly, Ptolemy himself recognized
that astrology stood upon a far shakier foundation than
astronomy.

Other ancient scientists also recognized that their astrological predictions were far less reliable than their astroomical ones. Nevertheless, confronted with even a slight possibility that astrologers could forecast the future, no king or political leader would dare to be without one. Astrologers held esteemed positions as political advisers in the ancient world and were provided with the resources they needed to continue charting the heavens and human history. Wealthy political leaders’ support of astrology made possible much
of the development of ancient astronomy.

Throughout the Middle Ages and into the Renaissance, many astronomers continued to practice astrology. For example, Kepler cast numerous horoscopes—the predictive charts of astrology—even as he was discovering the laws of planetary motion. However, given Kepler’s later descriptions of astrology as “the foolish stepdaughter of astronomy” and “a dreadful superstition,” he may have cast the horoscopes solely as a source of much-needed income. Modern-day astrologers also claim Galileo as one of their own, in part for his having cast a horoscope for the Grand Duke of Tuscany. However, while Galileo’s astronomical discoveries changed human history, the horoscope was just plain wrong: The Duke died a few weeks after Galileo predicted that he would have a long and fruitful life.

The scientific triumph of Kepler and Galileo in showing Earth to be a planet orbiting the Sun heralded the end of the linkage between astronomy and astrology. Astronomy has since gained status as a successful science that helps us understand our universe, while astrology no longer has any connection to the modern science of astronomy.

Does astrology have any scientific validity?
Although astronomers gave up on it centuries ago, astrology remains popular with the public. Many people read their daily horoscopes, and some pay significant fees to have personal horoscopes cast by professional astrologers. With so many people giving credence to astrology, is it possible that it has some scientific validity after all?

Testing Astrology

The validity of astrology can be difficult to assess, because there’s no general agreement among astrologers even on such basic things as what astrology is or what it can predict. For example, “Western astrology” is quite different in nature from the astrology practiced in India and China. Some astrologers do not make testable predictions at all; rather, they give vague guidance about how to live one’s life. Most daily horoscopes fall into this category. Although your horoscope may seem to ring true at first, a careful read will usually show it to be so vague as to be untestable. A horoscope that says “It is a good day to spend time with friends” may be good advice but doesn’t offer much to test.

Nevertheless, most professional astrologers still earn their livings by casting horoscopes that either predict future events in an individual’s life or describe characteristics of the person’s personality and life. If the horoscope predicts future events, we can check to see whether the predictions come true. If it describes a person’s personality and life, the description can be checked for accuracy. A scientific test of astrology requires evaluating many horoscopes and comparing their accuracy to what would be expected by pure chance. For example, suppose a horoscope states that a person’s best friend is female. Because roughly half the population of the United States is female, an astrologer who casts 100 such horoscopes would be expected by pure chance to be right about 50 times. We would be impressed with the predictive ability of the astrologer only if he or she were right much more often than 50 times out of 100.

In hundreds of scientific tests, astrological predictions have never proved to be significantly more accurate than expected from pure chance. Similarly, in tests in which astrologers are asked to cast horoscopes for people they have never met, the horoscopes fail to match actual personality profiles more often than expected by chance. The verdict is clear: The methods of astrology are useless for predicting the past, the present, or the future.Examining the Underpinnings of Astrology In science,observations and experiments are the ultimate judge of any idea. No matter how outlandish an idea might appear, it
cannot be dismissed if it successfully meets observational or experimental tests. The idea that Earth rotates and orbits the Sun seemed outlandish for most of human history, yet today it is so strongly supported by the evidence that we consider it a fact. The idea that the positions of the Sun, Moon, and planets among the stars influence our lives might sound outlandish today, but if astrology were to make predictions that came true, adherence to the principles of science would force us to take astrology seriously.

However, given that scientific tests of astrology have never found any evidence that its predictive methods work, it is worth looking at its premises to see whether they make sense. Might there be a few kernels of wisdom buried within the lore of astrology?
Let’s begin with one of the key premises of astrology that there is special meaning in the patterns of the stars in the constellations. This idea may have seemed reasonable in ancient times, when the stars were assumed to be fixed on an unchanging celestial sphere, but today we know that the patterns of the stars in the constellations are accidents of the moment. Long ago the constellations did not look the same, and they will also look different in the future. Moreover, the stars in a constellation don’t necessarily have any physical association, because two stars that are close together in the sky might lie at vastly
different distances. Constellations are only apparent associations of stars, with no more physical reality than the water in a desert mirage. Astrology also places great importance on the positions of the planets among the constellations. Again, this idea might have seemed reasonable in ancient times, when it was thought that the planets truly wandered among the stars. Today we know that the planets only appear to wander among the stars, much as your hand might appear to move among distant mountains when you wave it. It is difficult to see how mere appearances could have profound effects on our lives. Many other ideas at the heart of astrology are equally suspect. For example, most astrologers claim that a proper horoscope must account for the positions of all the planets.
Does this mean that all horoscopes cast before the discovery of Neptune in 1846 were invalid? If so, why didn’t astrologers notice that something was wrong with their horoscopes and predict the existence of Neptune? (In contrast, astronomers did predict its existence. Most astrologers have included Pluto since its discovery in 1930; does this mean that they should now stop including it, since it has been demoted to dwarf planet, or that they need to include Eris and other dwarf planets, including some that may not yet have been discovered? And why stop with our own solar system; shouldn’t horoscopes also depend on the positions of planets orbiting other stars? Given seemingly unanswerable questions like these, there seems little hope that astrology will ever meet its ancient goal of forecasting human events.

– The Cosmic Perspective (Bennett et al.)