The move away from an Earth-centered view of the Universe

Overview

Introduction
This topic provides a second major opportunity to study theory change in science. Students will have first met these ideas about science,12.1 d-l, in topic 9.1, Infectious Diseases and can now review them in a totally different science context. It also allows further development of 12.2 Social Influences.

A suggested route through the topic

Setting the scene
An introduction to encourage interest.

• Show pictures of the night sky. Students from big towns may never have seen it clearly.
• Show some striking images of the solar system such as those from the Voyager flights.

Early theories
This section illustrates 12.1 f, g, creative imagination and the use of models.

• A class discussion of how the solar system 'feels' to us to introduce Greek theories of the solar system. We talk about Sun rise, it does not feel as if we are moving.
• The story of just how much early astronomers did find out about the solar system, without sophisticated instruments, is impressive. Start with the achievements of ancient astronomers including the Babylonians in ancient Iraq. Their need for an accurate calendar led to a remarkable ability to predict astronomical events. They also developed the system of Zodiac signs later adopted by the Greeks.
• The achievements of other ancient civilisations such as India or China might also be mentioned to avoid the Eurocentric bias implied by starting with the Greeks. There are links to brief accounts from the Babylon site.
• Go over the way that the geocentric theory was gradually modified as new evidence became available. The final version, the Ptolemaic model was a very useful and accurate predictor of planetary motion.
• The SATIS 16-19 activity 52, the Problem of the planets explains the development of the Ptolemaic model.

The Copernican revolution and Galileo
This section can be used to illustrate many important ideas about science. These include 12.1 h, i, the use of observation to rule out alternative explanations and their inability to prove an explanation correct, 12.1 k reluctance to reject a well established explanation, and 12.2 social influences. Try to avoid a very simplistic 'Church versus Science' approach. See the discussion on this in the textbook.

• Discuss how complex and unsatisfying the Ptolemaic model is as an explanation.
• Find out what model students have and ask them why they believe this model.
• Describe the much simpler model proposed by Copernicus, which although no better at predictions was simpler and more satisfying.
• The Copernican model was adopted by three outstanding scientists, Brahe, Keppler and Galileo, who all played an important role in acceptance of the theory. It is only necessary to look at Galileo's actual work, whilst mentioning the equally important role of the others.
• The activity 'What did Galileo see?' (76 KB) can be used to demonstrate how difficult it can be to interpret observations unless you know what you are expecting.
• The SATIS 16-19 activity 1, the Trial of Galileo, is a drama activity that includes social influences.

Our understanding of the solar system
This section includes the science explanation of gravity as a field. It also provides two good examples of 12.1 j, predictions from theory that are found to agree with observation.

• The activity 'A feeling for Fields' (42 KB) is an experiment on magnetism to demonstrate the characteristics of a field model of action at a distance to help with an understanding of gravity.
• The work of Adams and Leverrier is a striking example of prediction and also of social influences.
• The Voyager missions demonstrate an accurate prediction.
• It also provide an opportunity to simply enjoy and wonder at the beauty of the images. Classroom illustrations would motivate students who find the theory hard going.
• The activity 'Solar system timeline' (27 KB) provides a review of the changing theories and encourages reflection on aspects of the scientific method.
• A discussion of the difference between astronomy and astrology might clarify some issues.

Evidence for an expanding Universe
All the work so far has been about the solar system. Better instruments have allowed us to begin to understand the Universe beyond our very small part. The interplay between theory and evidence is well illustrated here. Conjecture and imagination play an important role and data is very inexact. 12.2, the interests and concerns of society, are very different from those operating in Galileo's time. We actively encourage research that further removes humans from the centre.

• The activity 'Factors of ten' (32 KB) helps students to come to terms with the scale of the Universe.
• The story of the development of the Big Bang theory provides a good case study of a theory change. It includes the evidence for an expanding Universe, the reluctance of some astronomers to accept the theory and the accidental discovery of the radiation predicted by the theory.
• Students can rehearse their understanding of evidence for the Big Bang with the activity 'Dialogue concerning the Origin of the Universe' (42 KB).
• Many students will be interested in exploring the implications of our current understanding of the Universe through activities on the possibility of extra-terrestrial life. See activities 'E.T. can't phone home' (33 KB) and 'We should be so lucky' (37 KB).

This overview links the main issues that are required by the specification, with a few suggested extensions, but some students will want to use the large range of excellent resources to go beyond this. The web links pages detail some of these.