Asking introductory astronomy students to attempt to define the different types of solar system objects both prior to and after instruction can provide useful feedback for both students and instructors on how well the nature of and differences between the objects are understood. The initial definitions can serve as a diagnostic assessment, showing about which objects there are confusion and misconceptions, and the final definitions, if given prior to an exam, can serve as formative assessments, allowing students and instructors to see what instruction may and may not have been effective and where more instructional time could be spent.1 

Prior to any instruction or assigned readings on solar system topics, students were asked to write definitions for the terms planet, moon, asteroid, comet, and meteor. During the fall 2014 semester the pre-instruction definitions of N= 97 students were collected and analyzed. The numbers and percentages of...

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