We present the development of a construct map addressing the reason for the seasons, as a subset of a larger learning progression on celestial motion. Five classes of 8th grade students (N?=?38) participated in a 10-day curriculum on the seasons. We revised a hypothetical seasons construct map using a Rasch model analysis of students' pre/post-assessments followed by a closer examination of individual student explanations. Our proposed construct map is consistent with the "Framework for K-12 Science Education" [National Research Council. (2012). "Framework for K-12 Science Education." Washington, DC: National Academy Press] but includes a more nuanced discussion of critical conceptual and spatial connections. Movement up the construct map begins with learning foundational concepts about the Earth's motion in space and how observational patterns of the Sun relate to temperature changes. Movement into the upper levels of the seasons construct map occurs as instruction supports students in making sense of how the space-based perspective of their location on a spherical Earth can be used to account for observable patterns of change. However, our findings suggest that making this connection between Earth-based observations of the Sun and the motions and perspectives of the Earth in space is one of the major challenges that limit student progress in this domain. Findings have implications for instruction designed to support astronomy education as described by the "Next Generation Science Standards" [NGSS Lead States. (2013)" Next Generation Science Standards: For the States, By the States. Achieve, Inc. on behalf of the twenty-six states and partners that collaborated on the NGSS." Retrieved from: http://www.nextgenscience.org/next-generation-science-standards]. Instruction that supports progress along this construct map, and the larger celestial motion learning progression, must purposefully support the spatially complex connection between the Earth's motion in space and phenomena observed from the Earth's surface.