Page from Galileo’s “Starry Messenger”

Galileo’s “Starry Messenger” contained the first telescopic drawings of the moon to be published. Galileo showed the moon to be a solid body with irregular surface features. This drawing correctly shows mountain tops catching the sunlight and casting shadows, the length of which Galileo used to estimate the mountains’ height.

—Bruno, L.C. (1987). The Tradition of Science.

ones. The students recognize that each of their explanations may have seemed plausible until all the evidence was brought into play. Moreover, they were not embarrassed to give up an explanation that did not work when the evidence pointed in another direction. When such displacement occurs, scientific understanding advances.

At this point in the unit, Mr. Gilbert finds it very helpful to assign a take-home exam. Each student is asked to look at all the activities the class has completed thus far. The assignment is to select and then record in a summary table all the evidence that supports or refutes the class’ model of the phases of the moon. “You should consider each and every activity we have completed. Your job is to construct an argument for either the acceptance or rejection of your model. Pay particular attention to the data we gathered during our observations of the moon. What patterns in the data support or refute your model?”

Mr. Gilbert writes the assignment on the board:

  • Part 1: draw and label your model.

  • Part 2: list the evidence that supports your model.

  • Part 3: list the evidence that refutes your model.

  • Part 4: write 1) an explanation using science concepts for the phases of the moon; 2) a list of questions you now have about the motion of the moon.

  • Total: no more than 10 pages. It will be a major part of your grade for the unit.


This vignette illustrates how a wide variety of learning outcomes can result through different kinds of investigations by students. It also

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