Beyond the 3D Conception of an Orbital Model

Dr. Carolyn Keys argues ( that standards should embody “a language that connects the learning objectives with the types thinking and reasoning to achieve them.” They do not because “separation” is the hallmark of standards writing. Science education has intentionally separated content from process for a long time. Content objectives appeared as specific propositions and process objectives as generic behaviors in textbooks of the 1960s. Testing the former is rather straightforward but becomes mostly a test of reading ability. “Performance objectives” attempt to reunite the two domains but are very challenging to write and score. The 3 dimensions of the Next Generation Science Standards compound the original sin of separation with two generic categories (scientific practices and crosscutting concepts) aligned with every lesson about a “disciplinary idea” (a specific proposition found by grade level on a matrix). Consider thinking and reasoning about the phases of the moon (a “phenomenon” to “make sense of” in NGSS jargon). Commonly, teachers guide students in moving a small and large ball around a lamp to demonstrate orbital modeling (practice) and learn that the relative position of the moon changes the phase viewed on earth (the “idea” expressed as a proposition). Less frequently, teachers engage students in observing and recording the moon with respect to the horizon. Sometimes, students use themselves as the earth and extend a ball with their arm to represent the moon, then rotate their body in natural sunlight to observe changing phases. Linking a model (or a crosscutting concept) to specific knowledge is a trivial challenge. More challenging is to reconstruct the experience of moon-watching, whether of observations of the sky or the illumination of the ball, in terms of “frame of reference” coordinated with relative position and relative motion properly scaled. When this reconstruction is complete, the learner has a mental model of orbital motion capable of answering a host of questions. When a child in Austin Texas sees a crescent moon near the horizon at dinner time, how are the earth, moon, and sun positioned? What lunar phase will appear to an observer in Cali, Columbia that same night? For each observer, which way will the horns of the moon point? Often learners imagine that the earth’s shadow causes changes in the phase of the moon. The quarter moon, however, is a half-circle of light. Does the earth cast a shadow with a straight edge? (No) Alas, most crescent moons in comic strips are the letter C. When does a U.S. observer observe a letter C crescent (and not a reversed C)? (Early morning only—when the moon is waning). A conception of the earth, moon, and sun in motion, then stopped in different positions, generates the thinking required to answer these questions. The position of the observer on earth does not change the relative position of the moon, earth, and sun. The rotating earth changes the observer’s perception of the moon in the sky. Grasping how phases look and change for different observers taxes students of all ages—especially when cast as observing the earth from the moon (or Venus from an earth orbit). On the conception all else depends. The ladder of understanding this conception has many rungs. The a priori separation of process from content helps its ascent not at all. The task for the learner is one of cognitive reconstruction of experience and perception using the resources of astronomy and interactions with artifacts and others. It’s kinesthetic (moving the body), social, verbal, and spatial. Drawing is crucial. 3D learning fails to do justice to the challenge. We should take Dr. Key’s findings to heart. Now, picture the trace of the moon’s orbit with respect to the sun, not the earth. That’s a scaling challenge. Does the path loop to cross itself? Does the path make sinuous turns? (No and no) It’s not easy teaching science.

Published by Charles "Kip" Ault

Professor Emeritus, Science Education, Lewis & Clark Graduate School of Counseling and Education.

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