Asia-Pacific Forum on Science Learning and Teaching, Volume 6, Issue 2, Article 1 (Dec., 2005)
Shu-Chiu LIU
From geocentric to heliocentric model of the universe, and the alternative perspectives
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Students' Alternative Models of the Universe

Previous studies on children's concepts about the earth revealed their "egocentric" view which leads to notions such as the flat and static earth, absolute up-and-down direction in space, horizontal sky, etc. (Klein, 1982; Nussbaum, 1985; Baxter, 1989). These findings indicated that children tend to interpret reality based on their perceptive experience. The fact that the sun, for example, rises on one side of the horizon, travels through the sky, and sets on the other side, while the landscape does not move, often leads the child to the conclusion that the sun is orbiting the static earth. This kind of egocentric view may resist to change because it is compatible with everyday experience.

Liu's recent study on students' conceptions of the universe conformed the previous findings and uncovered several types of models, based on which students described and explained the earth and the heavenly bodies and events. The investigation was conducted with sixty-four third to sixth graders (8-13 years old) in Taiwan and in Germany by means of interviewing in a story form. Students were asked to play the role of the earth child and to have a conversation with an alien child who accidentally fell onto the earth during navigation. The questions presented in the interview concern the earth (its shape, motion, relative positions to the obvious celestial bodies, etc.) and the heavens (its meaning, characteristics of the heavenly bodies and reasons for day/night cycle and moon phases). They were intended to reveal not only verbal responses but also students' drawing, clay model making and demonstration using the clay. The same analysis technique as described in Vosniadou and her colleagues' several investigations (Vosniadou and Brewer, 1992; Vosniadou and Brewer, 1994; Diakidoy et al., 1997) is used in the study. The main results of the study are summarized in the following (also see Table 1)

Common features
  1. Elicited knowledge shows a model-like pattern.
  2. The student's model exhibits an either earth-centred or sun-centred view.
  3. The earth and the heavenly bodies seem to be confined in an "observable universe".
  4. A more scientifically correct model generally demonstrates a higher level of explanatory power.
Differences between German and Taiwanese students
  1. For the Taiwanese students, "reasoning" the phenomena in question does not seem to be always significant or necessary.
  2. Earth-centred view is dominant among the Taiwanese, whereas sun-centred view is mostly presented by the Germans.
  3. German students generally provide more accurate explanations to day/night cycle and moon phases than Taiwanese ones.

Table 1. Students' ideas about the earth and the heavens

A child's elicited knowledge appeared to be rooted in a model of the universe, which is often different from the accepted scientific one. Students conceive of the universe as being infinite, but, nevertheless, confine the basic astronomical objects - the sun, moon, earth, planets and sometimes stars - to an observable (or imaginary) space that has a centre of either the sun or the earth.

Group 1: Earth-Centred View Group 2: Sun-Centred View

Model 1: Static heavens with spinning earth

Model 4: Static sun with orbiting earth

Model 2: Cone heavens

Model 5: Static sun with orbiting earth and moon

Model 3: Earth-orbiting heavens

Model 6: Present-day model with static sun

Figure 1. Students'models of "the heavens and the earth"

It seems that these alternative models exhibit different levels of explanatory power (Thagard, 1992); the more advanced the model is, the higher explanatory power it exhibits. A considerable number of students, for example, in the group of "Model 6: present-day model with static sun" explained, in various levels of precision, the moon phases as a result of its movement and the consequent change of its illuminated area visible from the earth, whereas students in the group of "Model 3: earth-orbiting heavens" often believed that the earth's shadow is the reason for the same phenomenon.

The interview data also revealed that children's epistemological positions about reasoning play a significant role in the construction of their alternative models. Several students who specifically cited that there was no (physical) reason for the changing phases of the moon all presented relatively primitive models, where an imaginary horizon and an absolute up-and-down direction predominated. It can be argued that when a child does not seek to explain reality, her/his interpretation of that reality remains at a descriptive level.

Some differences between the students of the two cultural settings were also observed. First, the majority of the Taiwanese presented the earth-centred models, whereas their German counterparts held mostly the sun-centred models. Secondly, the explanations of the day/night cycle and the changing moon phases given by the German children are generally more (scientifically) accurate than those by the Taiwanese. Thirdly, it seemed that to reason the phenomena under study was a more "natural" or "legitimate" task for the German students than for the Taiwanese ones; that is, the former seemed to answer readily the why-questions, no matter the answer was correct or not, while the latter often puzzled in the first place, and sometimes even did not hold that there was a reason at all.

The following discussion does not go into detail with the cultural difference, but rather focuses on the model-like structure of the elicited knowledge from both the Taiwanese and German young students. Based on students' alternative conceptions as revealed, it is argued that there is a potential for the use of pre-scientific models in helping students distinguish and improve their own views.

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