1-1 Astronomy is both an ancient cultural practice and a cutting-edge science

Wondering about the night sky has a rich heritage that dates back to the myths and legends of antiquity. Centuries ago, the heavens were thought to be populated with demons and heroes, gods and goddesses. Astronomical phenomena were often explained as the result of supernatural forces and divine intervention and were used to remind Earth-bound inhabitants that their lives are intimately connected with the goings-on in the sky.

There is no single sequence of steps followed in all scientific investigations. All scientific methods use multifaceted observations and logical inference to pursue questions about the natural world.

The course of civilization has been greatly affected by a profound realization: The universe is comprehensible. This awareness is one of the great gifts to come to us from the great thinkers of ancient Greece. Greek astronomers discovered that by observing the heavens and carefully reasoning about what they saw, they could uncover something about how the universe operates. For example, as we will see, they measured the size of Earth and were able to understand and predict eclipses without imagining supernatural forces. Modern science is a direct descendant of the work of these ancient Greek philosophers.

Variety of Scientific Methods

Like musicians, philosophers, or advertisers, scientists are people who make use of creativity, intuition, and experience. Although many people learn how to scientifically study the universe in college, there is no such thing as an official scientist’s license to be purchased or a formal scientist certificate to be granted before someone can call him/herself a scientist. Instead, individuals call themselves scientists when they follow a scientific method and agree to its code of ethics.

What is a scientific method? Throughout much of our schooling, we have often learned that the scientific method is a boring, nonimaginative, step-by-step way of studying the world by first making predictive hypotheses and then designing experiments to prove that a hypothesis is correct. We often read that this scientific method is supposedly free from any subjective human emotions and is based entirely on observed facts. While this sounds appealing, science does not actually work this way.

You might be surprised to learn that a seemingly simple story of scientists following the specific step-by-step approach of a scientific method is not how the science of astronomy is actually done. Instead, the truth of the scientific enterprise is actually far more interesting. The real process of humans conducting scientific exploration is filled with twists and wrong turns, epic failures and glorious triumphs, surprising insights, and sometimes catastrophic accidents. Let’s consider some of characteristics of how science is done.

There is no single sequence of steps followed in all scientific investigations. In other words, there is no single scientific method with specific steps that everyone follows identically. There are, however, several attributes that are common across scientific studies: All scientific methods use multifaceted observations to pursue consistent evidence when trying to answer questions about the natural world. All scientific investigations are centered on pursuing a question or an unexpected observation, but they do not necessarily test a hypothesis.

A hypothesis is traditionally defined as a collection of thoughtfully proposed mechanisms for how the world operates or a comprehensive and complete explanation for why particular observations are seen. Hypotheses are weighed by the degree to which they can accurately make testable predictions. However, astronomers rarely devise and test hypotheses through experimentation; instead, astronomy is generally an observational science.

Let’s start with an example. Imagine you are growing fruit and you want to know how much fertilizer to put on apple trees in order to make them grow as much fruit as possible. One scientific approach to studying fruit trees and fertilizer is to make a hypothesis that apples trees grow better with fertilizer than without fertilizer. The next step would be to plant 50 trees without any fertilizer and 50 trees with fertilizer as an experiment. Finally, after waiting for a few months, you could count which of the two groups of trees produced the most apples and determine if your hypothesis about apple trees with fertilizer producing more apples was correct. This is an example of a traditional, two-group comparison approach to the scientific method.

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There are, however, other approaches to pursuing the question of how to grow more apples. A different scientific method of studying the relationship between apple tree production and the use of fertilizer could be to plant 100 apple trees, put slightly increasing amounts of fertilizer on each tree, and then count the number of apples produced in terms of how much fertilizer was applied. Because some trees would have too little fertilizer and other trees would have too much fertilizer, this scientific study result would be a graph revealing the optimal amount of fertilizer for growing the most apples. Like the initially described study, this second scientific study described the responses of apple trees to fertilizer. Although the first study tested a hypothesis and the second study did not, both are completely valid scientific methods.

Scientists Develop and Test Theories

Rather than hypotheses, astronomers deal largely with developing and refining theories. A body of related observations can be pieced together into a comprehensive, self-consistent explanatory description of nature called a theory. In fact, many astronomers go their entire career and never create and test a single hypothesis. From the above example about how to best produce lots of apples, the theory being studied was that there exists an optimum amount of fertilizer to maximize an apple tree’s production.

An astronomy example from later in this book is the theory that the planets are held in their orbits around the Sun by a gravitational force between the Sun and planets (Figure 1-1). Without theories that make broad statements about the natural world, there is no understanding and no science, only long collections of disconnected facts. In fact, it is when widely encompassing ideas come together to form a theory that one can predict the outcome of experiments and observations that the scientific method is at its peak performance.

CAUTION

In everyday language the word “theory” is often used to mean an idea that looks good on paper, but has little to do with reality. In science, however, a good theory is one that explains reality and that can be applied to explain new observations. An excellent example is the theory of gravitation, which was devised by the English scientist Isaac Newton in the late 1600s to explain the orbits of the six planets known at that time. When astronomers of later centuries discovered the planets Uranus and Neptune and objects like Pluto, they found that these objects also moved in accordance with Newton’s theory. The same theory describes the motions of satellites around Earth as well as the orbits of planets around other stars.

The most widely accepted scientific theories are ones that make accurate predictions that can be independently tested by other scientists. If the predictions are verified by observation, this lends wider support to a proposed theory and suggests that it might be a reasonably accurate description of how nature operates. Alternatively, if a theory’s predictions are not verified, the theory needs to be modified or completely replaced.

For example, an old theory held that the Sun and planets orbit around a stationary Earth. This theory led to certain predictions that could be checked by observation, as we will see later in this book. In the early 1600s the Italian scientist Galileo Galilei used one of the first telescopes to show that these predictions were incorrect. As a result, the theory of a stationary Earth was rejected, eventually to be replaced by the modern picture shown in Figure 1-1 in which Earth and other planets orbit the Sun.

Figure 1-1: Planets Orbiting the Sun An example of a scientific theory is the idea that Earth and the other planets orbit the Sun because of the Sun and planets’ gravitational attraction. This theory is universally accepted because it makes predictions that have been tested and confirmed by observation.

CAUTION

Sometimes, scientists refer to universal laws. Some people mistakenly think that once a scientific theory is proven, it is elevated to the status of a law, such as the law of gravity. In science today, some things are referred to as “laws” for historical reasons because people used to believe the laws were completely true and would stand forever and we have used that name for a long time. However, one of the important characteristics of science is that scientific knowledge and theories are always open to being revised with new observations—and the term law is rarely used any more. A comprehensive theory, not a law, is what many scientists aspire to create.

In astronomy, a theory that cannot be tested by observation or experiment does not qualify as a scientific theory. An example is the idea that there is a little man living in your refrigerator who turns the inside light on or off when you open and close the door. The little man is invisible, weightless, and makes no sound, so you cannot detect his presence. While this is an amusing idea, it cannot be tested and so cannot be considered science.

Scientific Theories Can Change

Like observation, informed skepticism is an essential part of all scientific methods. New theories must be able to withstand the close scrutiny of other scientists. The more radical the theory, the more skepticism and critical evaluation it will receive from the scientific community, because the general rule in science is that extraordinary claims require extraordinary evidence. That is why scientists as a rule do not accept claims that people have been abducted by aliens and taken aboard UFOs. The evidence presented for these claims is unverifiable.

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At the same time, scientists must be open-minded. They must be willing to discard long-held ideas if these ideas fail to agree with new observations and experiments, provided the new data have survived evaluation. That is why scientific knowledge is always subject to change. If, for example, an alien spacecraft really did land on Earth, scientists would be the first to accept that aliens existed—provided they could take a careful look at the spacecraft and its occupants.

The most productive scientists are diligently open to considering alternative ideas, particularly when presented with new evidence. This is true because one of the characteristics of science is that the specific way a particular observation is made can dramatically influence the results. Consider, for example, that a large telescope on Earth’s surface obtains very different views of our Sun than much smaller space telescopes. Orbiting our planet above Earth’s obscuring atmosphere, space telescopes have special instruments that provide very different views of the same object, as can be seen in different ground-based and space-based telescope images of our Sun. These views are valuable, but show different aspects of the Sun because the different methods obtain different results. Moreover, even two astronomers looking at the exact same set of images may decide that the data reveal very different things. This is not about making an error; but it is about people arriving at different conclusions based on the same data.

Ethics in Science

Earlier, we hinted at the idea that science is fundamentally a human endeavor and, as such, is subject to much of the same celebration, conflict, and missteps as any other human activity. For example, scientists often compete to be the first person to make a new discovery. Just as many Olympic athletes try to be the fastest record holder in a racing event, scientists who are first to make an important discovery are widely celebrated. For example, many people have tried to discover new comets, but one comet hunter is probably more famous than all others, Edmund Halley of the famed Comet Halley.

Celebrated scientists are often rewarded with high-paying jobs and are invited to travel to distant locations to present the results of their research. At the same time, sometimes the desire to be the first scientist to announce a new discovery or to be proven correct can result in unethical behavior—just as it occasionally happens in sports, where the drive to win at all costs overcomes a moral judgment.

People who do science informally agree to an unwritten code of ethics. This code generally includes working to benefit the world without causing harm. It also means that scientists should be honest and transparent about their observational and experimental strategies and publicize their results for public review. Scientists also allocate time to reviewing the scientific work of other scientists. Perhaps most importantly, scientists agree to publicly acknowledge the intellectual and financial contributions of all others from whose work they have drawn while not falsifying scientific data or being otherwise deceitful in their work. Many scientists also accept responsibility for training the next generation of upcoming scientists and future teachers. As stated by Bruce Alberts, former president of the National Academy of Sciences, “honesty, generosity, a respect for evidence, and openness to all ideas and opinions” can be considered a summary statement about the scientific code of ethics.

While we recognize that there is not a single scientific method, we also must recognize that not all questions are appropriate for scientific investigations. Important questions about what it means to be human—such as what is love, how valuable is truth, and what is the purpose of life—are tremendously important intellectual pursuits but are not necessarily the types of questions science can answer. Rather, the questions that science can best address are those about physical processes governing the natural world—questions for which numerous observations and carefully planned predictive tests can be made and evaluated using logical inference, and a bit of informed skepticism.

Technology in Science

Go to Video 1-1

As we will see in Chapter 2, in recent years astronomers have constructed telescopes that can detect such nonvisible forms of light (Figure 1-2). These instruments give us views of the universe vastly different from anything our eyes can see. These new views have allowed us to see through the atmospheres of distant planets, study the thin but incredibly violent gas that surrounds our Sun, and even observe new solar systems being formed around distant stars. Aided by high-technology telescopes, today’s astronomers carry on the program of careful observation and logical analysis begun thousands of years ago by their ancient Greek predecessors.

Figure 1-2: RIVUXG A Telescope in Space Because it orbits above most of Earth’s obscuring atmosphere, the Hubble Space Telescope (HST) can better detect nonvisible forms of light absorbed by our atmosphere that are difficult or impossible to detect with a telescope on Earth’s surface.

Scientific advancements often depend on the development of new technology. For example, it was not until the use of telescopes in the seventeenth century that astronomers came to widely agree that the planets orbit our Sun. The new technology of the telescope provided observations about the changing appearances of planets and motivated a new scientific theory to replace one that was deeply entrenched in society.

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As our technology increases, with computers squeezing vast amounts of digital memory in smaller and smaller places and cell phones having longer and longer battery lives, new tools for research and new techniques of observation dramatically impact astronomy. For example, tiny digital cameras are commonly integrated into cell phones, and this same technology can be used to make ultrasensitive cameras that work with telescopes. As another example, until fairly recently everything we knew about the distant universe was based on a narrow band of visible light. By the end of the nineteenth century, however, scientists had begun discovering forms of light invisible to the human eye: X-rays, gamma rays, radio waves, microwaves, and ultraviolet and infrared radiation.

A Quick Guide to Objects in the Sky

The science of astronomy allows our intellects to voyage across the cosmos. We can think of three stages in this voyage: from Earth through the solar system, from the solar system to the stars, and from the stars to galaxies and the grand scheme of the universe (see Cosmic Connections: Size and Structure of the Universe).

The star we call the Sun and all the celestial bodies that orbit our particular star—including Earth, the other seven planets and all their various moons, and smaller bodies such as dwarf planets, asteroids, and comets—make up the solar system (Chapter 4).

The nearest star to Earth is the Sun. All stars emit energy in the form of light, so all stars shine. Stars change over time and have life stages that we will discuss later (Chapters 10, 11, and 12). A few key points about stars help set the stage for us here:

Stars are not spread uniformly across the universe but are grouped together in huge assemblages called galaxies (Chapters 13 and 14). A typical galaxy, like the Milky Way, of which our Sun is part, contains several hundred billion stars.

We will begin our voyage from Earth to the distant reaches of the universe just as our ancestors did, by looking up from Earth into the sky and carefully studying the objects we can see with our eyes.

Question

ConceptCheck 1-1: Which is held in higher regard by professional astronomers, a hypothesis or a theory? Explain your answer.

Answer appears at the end of the chapter.