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Asia-Pacific Forum on Science Learning and Teaching, Volume
7, Issue 2, Article 1 (Dec., 2006) Shu-Chiu LIU Historical models and science instruction: A cross-cultural analysis based on students’ views
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Instructional use of historical material
Through the previous discussion of historical and students’ knowledge regarding the Earth and the sky, some common underlying principles between them can be brought to light:
1. Their structural form: Not only early scientists but also today’s students construct a model of the universe through which they describe and explain astronomical objects and events. These models may exhibit various degrees of precision and coherence, yet in general maintain a self-sufficient structure before new questions or evidence come forth.
2. Essentially based on perception: To let either the Earth or Sun place in the middle of their models, and be the dominant power over the movements of other celestial bodies is a perspective relying on sensorial evidence. So is the idea of the Earth being flat as well as the view to confine all the visible objects in the sky to an imaginary space. These are found evident in both students and history.
3. Cognitive progress as a function of reasoning: The move from merely describing to reasoning natural phenomena seems to be an essential step for model modification. Students who do not intend to explain causal connections within the model seem to consequently hold a relatively primitive model. Similarly, Chinese models underwent hardly any progress as their scientists did not seek to go beyond facts and look for reasons.
These common features may act as an indicator for us to transform historical material into a form for instructional use. Their presence calls for an examination of the ways in which pre-scientific models are generated and revised, so that we can further reflect on teaching strategies that can help our students to recognize and rethink about their models. It should be noted that in studying cross-culturally the significant points of conceptual development in science, some essence of science itself comes to the surface as well as underlying principles of the particular concept and model. Some instructional suggestions of using historical material are thus evolved based on the present analysis of students’ and historical ideas regarding the universe:
Historical models for students’ understanding of the perspective beyond the surface of the Earth
Liu’s investigation shows that students’ elicited models of the universe fall into two groups: Earth-centered and Sun-centered views, similar to the geocentric and heliocentric models which characterized the astronomical development in Europe. As the essential difference between the geocentric and heliocentric views is the perspective taken on the surface of the Earth and beyond, it should be therefore a high point for instruction to use the historical models. To be more precise, the geocentric and heliocentric perspectives of historical models can be introduced to students in relation to the understanding of the perspective on the surface of Earth and beyond; the former is constrained by the experience and observation based on the surface of the Earth, whereas the latter was regarded as the first step that man goes beyond the surface of the Earth to view the universe. Students do have similar difficulty to take a different perspective beyond where they are located. When they are able to move from the perspective on the Earth to that beyond, they are on the way towards understanding the intended scientific knowledge, and, moreover, the process this understanding is achieved.
In addition, students’ difficulty in relating the flat Earth as viewed on the surface of Earth to the spherical Earth as explained by other people is similarly derived from the perspective students take from where they locate. To understand the spherical shape of Earth, the student must first realize there is a difference between what is seen on the Earth (while the observer is a tiny point as opposed to the whole Earth), and outside the Earth (while the Earth can be fully captured in the view). The historical models of the Earth can be therefore placed in the students’ learning process for understanding this distinction. For example, the historical intuitive ideas about the shape of the Earth, such as Homer’s shield-like Earth, Anaximander’s cylindrical Earth, and the disk- or plate-like Earth held by early Chinese scientists for centuries, are those that can be understood as the perspective taken on the Earth’s surface. In contrast, a spherical model of Earth was established in the Greek antiquity as early as in the sixth century B.C. along with several primary and convincing arguments, such as “the ships approaching the shore appear first with its mast” and “the shadow of the Earth cast on the Moon during an eclipse is always round” so that the Earth must be round. To illustrate these arguments may assist students in taking a different perspective beyond what one merely sees.
Intercultural historical material for students’ understanding of “the structural view of nature”
A structural view of nature is essential to science. It denotes the premise that nature can be described and explained through logically coherent theories. Without a structural view of nature, natural phenomena cannot be regulated into a whole and all bits in scientific theories cannot be summed up into certain rules or fundamental hypotheses, from which one can make logically consistent deductions by means of formal logic. This view highlights a search for reasons and evidence rather than a mere description of reality. It is claimed to be the driving force, by which European astronomy was moving towards a more coherent view, and in contrast, in absence of this view the early Chinese astronomers failed to progress their models.
The historical material from these two cultural contexts can be therefore operated to assist students in forming a structural view of nature. As discussed previously in the paper, it seems that the scientists in early China have never established the structural view of nature, which led to their theories being less logically structured than those in Greek antiquity. The ancient Chinese astronomers, unlike their Greek counterpart, did not give emphasis to efforts on regulating celestial phenomena, despite a different perspective they provide, and consequently on testing the derived regularities. As a consequence, their models of Heaven and Earth were prevailing without significant improvement for about two millenniums until the Western scientific concepts became known in the seventeenth century. This aspect indicates how significant it is to establish a structural view of nature and an understanding of the function of experiment in scientific theory that should have much implication to students’ conceptual development.
The Copernican Revolution can serve as another example to teach about this, as Copernicus was the first in written history to single out the form of a theory, and to argue for a systematic, harmonic, and logically coherent astronomy. He criticized Ptolemaic astronomy as being “fundamentally hypothetical,” within which everything is isolated and independent and thus can be freely changed whenever a need emerges. This historical chapter can not only tell students something about the nature of science but also help them to reflect upon their own views in terms of structure.
Historical material and hands-on experience
Historical concepts and models are intertwined with observations and experiments that early scientists carried out to seek for evidence. It is fundamentally through sky-gazing that the early astronomical models were constructed, as technological instruments were actually modern products, discovered as late as in the seventeenth century. It should thus be reasonable to expect that students may revise their concepts and models if watching the sky carefully. The child who, for example, described the Sun and Moon as orbiting the Earth and staying on two sides of it would soon realize that they sometimes appear together in the sky by means of regular observations. It is also relatively easy to remove some particularly naďve concepts such as the Moon phases resulted from clouds’ obstruction, as indicated in several studies including Liu’s, if a sky observation is carried out cautiously. Moreover, through the observation of the Sun, Moon and stars, from different angles, e.g., from the sea (horizon), students may develop a sense of spatial relations of heavenly bodies and the Earth.
Some more attention should be give to the role of early experiments in developing ideas and models. Students should learn about and can even re-do these experiments that brought about plausible pre-scientific arguments. One good example is the famous experiment done by Erathostenes (276-194 B.C.) of Alexandria; by measuring lengths of the stick shadow at the same time in different places with known distance, the concept of the spherical Earth was proven and its circumference was precisely calculated. It could be introduced and even replicated in the science classroom to lead the student to the understanding of the spherical shape of the Earth.
Educational research has pronounced the importance of hands-on experience in science learning processes. It is important to plan teaching and learning projects starting with direct observation and the contact with natural objects and events, and enhancing students’ inquiry into nature by genuine personal experiences. As Vosniadou & Ioannides (1998) argued, “In order to persuade students to invest the substantial effort required to become science literate and to re-examine their initial explanations of physical phenomena, we need to provide them with additional meaningful experiences (in the form of systematic observations or the results of hands-on experiments), that prove to them that the explanations they have constructed are in need of revision” (p. 1224). It is therefore of significance to disclose the role and the value of the early activities involved in the development of scientific ideas and models in view of their connecting point to students’ science learing.
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