Introduction

It is not obvious that the Earth is orbiting the Sun and not the other way around. If anyone has ever given you that impression, take a moment to say “shame on them,” and then consider the world around you. The Earth appears to be unmoving, the wind blows in every direction, and water flows downhill, settling as close as it can to the centre of the Earth. If you carefully watched the Sun throughout the day, or the stars throughout the night, you would see that they make concentric paths across the sky and you might therefore imagine that the Earth is spinning (despite the fact you can’t feel it spinning), and that it is thereby giving the illusion that the Sun and stars are circling around it. This thought has occurred to people for thousands of years, and it is certainly no basis for believing that the Earth must be spinning, let alone for accepting that the Earth is orbiting the Sun.

Indeed, there are very good reasons for accepting that the Earth is spinning and orbiting the Sun; but before certain discoveries were made during the 17th century, which finally pointed to that, there were better reasons for accepting that the Sun, Moon, stars and planets are all orbiting the Earth. There were actually very good reasons for thinking so, and they were not just the obvious ones, but ones constrained through careful astronomy—a word that literally means “patterns among the stars”—by comparing careful measurements with the different hypothetical explanations.

The Scientific Revolution which took place in the 16th and 17th centuries is not the story of a few people with the audacity to rise up and challenge ancient and honoured views which were so obviously wrong that anyone with half a brain and a backbone would have done the same. That unfortunate misconception not only undervalues the great achievements of people like Copernicus, Galileo and Kepler, but unfairly paints a picture of their contemporaries—as much as the scientists who preceded them—as pigheaded buffoons.

It would be fairer to say that the Scientific Revolution was the inevitable next step in the human search for explanation and understanding of our world. As you will see in this module, humans have always been curious about the Universe we live in, and have worked for millennia to develop consistent explanations of celestial phenomena.

There is not a lot that we can infer from the prehistoric record except that many cultures around the world did track the objects of the night sky and knew their patterns. This gathering of evidence for the purpose of discovering patterns is an important part of what we now call science. So is the interpretation of those patterns—and a fair estimate would be that there have been as many different interpretations of patterns in the night sky as there have been cultures on Earth.

Along with knowledge about the phenomena and an ability to interpret basic causes, what people really needed to move forward was a system that would allow them to sort out which interpretation is correct. Part of that system, which was first mastered by the ancient Greeks and which we continue to use, is logic. We will discuss how logic fits into the scientific method in more detail below; but for the purpose of this introduction we need only note that, by using logic and working from clearly evident principles, Aristotle managed to construct a highly complex, self-consistent theory which was so powerful that, despite being completely wrong (because the clearly evident principles were wrong, though the logical consequences derived from them were sound), it did not topple for 2000 years.

Aristotle’s was a scientific theory. From the evidence that was available to him, he derived the first principles of his logical system and deduced consequences. Thus, the explanation of every potential observation in nature was based on the evident principles, and through Aristotle’s logical system predictions could be made. And for 2000 years, no clear contradiction was discovered.

In science, it is important to note that nothing is ever proven to be true; you should never hear a scientist say that any hypothesis has been proven through some observation. What we do most of the time (because we have a pretty good idea about the world and what to look for) is verify predictions that are based on a few key assumptions—the first principles, or hypotheses about the world we live in. Verification is a key part of the scientific method, and we always try to verify predictions as many times, and by as many independent means, as we are able.

Perhaps more important than verification, however, is falsification. This is the hallmark of modern science, which enables us to distinguish whether a theory is potentially correct or wrong. A theory that is not falsifiable is not scientific; in fact, falsifiability has often been adopted as the defining feature of scientific theories. Indeed, Galileo’s discoveries in the early 17th century, of a number of striking contradictions with the hypotheses of Aristotelian physics, were so important because they falsified key principles and shook the foundations of physics.

The major aspects of the scientific method developed along with our discovery of the Solar System. These will be discussed in detail throughout this module, as we begin exploring how that discovery took place over time. Thus, we will eventually see not only how human curiosity brought us to an accurate description of celestial orbits, but also to a method through which all subsequent scientific investigation would take place.