Observations vs. Explanations
In this classroom activity students are asked to put themselves in the place of the first scientists who explained the origin of the Solar System. In groups, they make a list of observations they would try to make if they were trying to come up with such an explanation. The class then discusses the answers given by the different groups and the instructor then describes some of the observations upon which scientists did end up basing their explanation. This simple activity was designed to help students start thinking more like scientists, but it never fails to expose student misconceptions about the nature of observations vs. explanations.
Process of Science GoalsStudents should learn to separate the observations upon which scientists base their explanations from those explanations. Scientific observations tend to be relatively durable, but more than one explanation for any set of observations is always possible. If students are to learn to rationally evaluate scientific claims, they need to be able to pick out which parts of these claims are the most durable (observations), and which are creations of the scientific imagination (explanations).
Context for Use
Description and Teaching Materials
Teaching Notes and Tips
Many student responses during this activity reflect this kind of misconception. Here are a couple of examples.
- Usually one of the groups will say that if they wanted to explain the origin of the Solar System, they would determine where the Sun is in "the life-cycle of a star." I point out that we can't observe the life-cycle of a star, which may span billions of years. All we can do is make various observations about whatever stars, nebulae, etc., we can see during a relatively short period of time. The "life-cycle of a star" is essentially a story constructed to explain those observations.
- Another group always says that they would observe what the Sun and other objects in the Solar System are made of. I consider this a good answer, given the stage of the course at which we do this activity. But when we discuss this answer I point out that, depending on what the students mean, it might reflect a somewhat more subtle version of the misconception. We can collect and analyze meteorites and materials in the Earth's crust, hydrosphere, and atmosphere, for example, but cannot go collect samples on the Sun or most of the planets. However, we can compare the absorption spectra of stars and planets with the spectra generated when light passes through the different elements here on Earth.
Here are some examples from other topics that come up in my class.
- Plate Tectonics: If you were in Alfred Wegener's place, what observations could you make to gather evidence for/against the idea that the continents were formerly in different places? Some students might answer that they would measure the movement of the continents, but at that time this wasn't feasible. Rather, it was an inference based on other observations like the distribution of Paleozoic glaciation, fossil organisms, mountain ranges, and so on.
- Geologic Time: What kinds of evidence do you think might have led the original geologists to conclude that the Earth is many millions of years old? Students should come away realizing that you have to combine observations of how long various processes take with the principle (assumption) of Uniformitarianism.
I also create multiple-answer questions for quizzes and tests in which I ask, "Which of the following are observations that are explained by [X theory]?" Some of the possible answers are always elements of the theory that are not observations.