This study investigated elementary students' explanations for the daily patterns of apparent motion of the Sun, Moon, and stars. Third-grade students were chosen for this study because this age level is at the lower end of when many US standards documents suggest students should learn to use the Earth's rotation to explain daily celestial motion. Interviews with thirdgrade students (n = 24), prior to formal astronomy education, revealed that about half are working from naive mental models. The other half of the students used more scientific explanations for the Sun's apparent motion but used scientific descriptions or explanations of the Moon's and stars' daily apparent motion far less frequently. We also describe an instructional approach designed to support students as they move between the Earth-based and heliocentric frames of reference using computer simulations and modelling with hands-on and kinaesthetic strategies. This instruction was tested with another group of third-grade students as part of their gifted programme (n = 16). Pre/post-interview analysis supports the instructional approach as the students showed a more sophisticated ability to move between the Earth-based and heliocentric frames of reference. The students' high initial knowledge level, entering instruction at the more advanced end of the general third-grade student population, limits our ability to generalize the instructional findings; however, these findings provide an important step in improving our understanding of how to support students in this complex area of astronomical reasoning.
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