Overview
Sir Isaac Newton famously said, “If I have seen farther it is by standing on the shoulders of giants.” In this module, we begin our exploration of the main developments that led to our description of the Sun, Moon and planets as a Solar System. There are two main reasons why we study these historical developments. The first is that they provide the most direct path to understanding why we should believe that the Earth and all the planets orbit the Sun: through the rejection of alternative hypotheses in light of empirical data. That, in a nutshell, is the scientific method. The second reason why it is important to study the early history of Astronomy is that, as the quote from Newton indicates, if we want to see what he saw—and if we want to see what Einstein saw after him—we need to get up onto the shoulders of the giants who came before.
In module 3 we will explore Newton’s universal law of gravitation as well as Einstein’s theory of gravity—general relativity. Module 3, which covers the shift from an Earth-centred, or geocentric view of the cosmos, to a Sun-centred, or heliocentric one, provides a key element in the development of human understanding that led to Newton’s discovery. But in order to appreciate what was really achieved by Copernicus, Kepler and Galileo during the Scientific Revolution, and thus fully grasp the power of the scientific method, it is important to first see how nascent science—and not simply ignorance—did favour a geocentric theory, and led to a sophisticated description which, for more than a millennium, was thought to be correct.
In modules 2-3, we will come to our modern theory of Solar System mechanics by assuming nothing about the cosmos except what we can observe in the sky, the hypotheses we can make on the basis of those observations, and the consequences that can be deduced as a result. This is the process of scientific discovery, an overarching theme in this course which will be frequently highlighted throughout, while we consider the evidence that was gathered over time and the ways that people fought to interpret it. In the current module, we will explore the details of the scientific process through the earliest developments in astronomy—examining what makes for “good science,” as we learn how exceptionally good science initially pointed to geocentrism rather than heliocentrism. In the next module, we will see how continuation of the scientific pursuit of understanding eventually showed that this was wrong.
Learning Objectives
When you have finished this module, you should be able to do the following:
- Relate how astronomy developed as a science up to the Ptolemaic model.
- Discriminate between “observable phenomena” and “things that happen or exist,” and explain why multiple hypotheses, such as geocentrism and heliocentrism, can potentially explain a particular phenomenon.
- Draw on empirical evidence in order to assess the validity of hypotheses.
- Demonstrate the phenomenon of parallax, explain its importance in astronomy, and use it to illustrate the vastness of space.
- Use empirical evidence to show that the Earth is spherical, and describe Eratosthenes’ method of measuring its radius/circumference.
- Assess the difficulty in obtaining precise astronomical measurements, and examine subsequent steps that may be taken in formulating scientific models.
- Describe the different elements of the Ptolemaic model and relate the particular function of each.
- Critically examine the scientific method, evaluating its strengths and limitations.
Key Terms and Concepts
- Phenomenon
- Scientific Method
- Hypothesis
- Geocentrism
- Heliocentrism
- Parallax
- Model
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