Powerful new observations and advances in computation and visualization have led to a revolution in our understanding of the structure, composition, and evolution of the universe. These gains have been vast, but their impact on education has been limited. Determining the range and frequency of “alternative conceptions” is an important first step to improving instructional effectiveness. Through analysis of pre-instructional open-ended surveys (N ~ 1250), follow-up interviews, and other assessments, our research group has been classifying students’ ideas about concepts important to modern cosmology, including the distances, structure, composition, age, expansion, and evolution of the universe. Informed by our research on student learning, we have created a series of web-based cosmology learning modules in which students master the scientific concepts and reasoning processes that lead to our current understanding of the universe, through interactive tasks, prediction and reflection, experimentation, and model building. This curriculum will fill the need for research-based educational resources in the rapidly changing field of cosmology while serving as a model for transforming introductory courses from primarily lecture- and book-based to a more engaging format.