Teaching the seasons: the role of diagrams

An aspect of thinking like a physicist is the ability to interpret visualisations of phenomena. Diagrams are therefore a common feature of the physics classroom. If you are anything like us, you are likely to have favourite figures that you feel convey a context particularly effectively. Tools like Google Images make a range of similar, but subtly different, diagrams readily accessible.

When choosing a diagram, it is worth considering how its features might affect how your students learn. Teaching the origin of the Earth’s seasons is a context in which diagrams can support students’ understanding and teachers might reflect carefully on the form of image they use.

A study by Victor Lee, of Utah State University, reports the impact of making small changes to diagrams of the Earth’s orbit on students’ conceptions of the seasons. Lee recruited 652 students aged 14-15 and asked them to complete the sentences: ‘It is warmer in the summer because…’ and ‘It is cooler in winter because…’ The students then looked at one of six versions of an orbital diagram and repeated the explanation task. The six diagrams varied on whether the Earth’s orbit was represented as a circle or as an ellipse, the perspective of the view (overhead or slanting), if the axial tilt was highlighted using a line, and whether coloured shading was applied to highlight day and night.

In the initial explanation, around 45% of the participants gave a scientifically correct response related to axial tilt. A further 15% gave explanations based on the location of the Earth in its orbit and 23% of explanations were based on the Earth-Sun distance. After viewing the diagrams, the total number of students producing axial-tilt explanations remained roughly constant. An unsurprising finding from such a brief and low intensity intervention.

The results did however reveal several interesting findings. First, no difference was caused by exposure to circular or elliptical orbital diagrams. Second, Lee found that one diagram in particular (below) - depicting an elliptical orbit with shading to indicate night and day and highlighting the Earth’s axial tilt – produced more scientifically correct explanations.

Lee notes that shading areas of light and dark on the Earth appears to cue the use of side-based explanations, which link the origin of the seasons to the location of the Earth in its orbit. However, this effect seems to be mitigated by the perspective view of the solar system shown above, where the viewing angle appears to be tilted. This presentation seems to emphasise a focus on axial tilt. The sample size of the study raises caveats about the potential generalisability of the findings.

Beyond the findings for the context of teaching the seasons, the study illustrates how pedagogic decisions about apparently minor details, such as the shading or labelling of a diagram, can have significant consequences for learning. It is worth reflecting on theassumptions you make when planning, evenat a fine-grained level of detail. Why this image rather than an alternative? What is the clearest wording of this explanation? How might this demonstration be most effectively set up? A joy of physics teaching is that, even for expert teachers, there are always incremental changes to be made to hone your practice.