Many elementary school students find astronomical knowledge difficult to attain. Students cannot observe planetary motion in the universe, which makes the construction of astronomical knowledge abstract and incomprehensible for many students. To cope with this dilemma, this study proposed creative situated learning via augmented reality (AR) and developed an AR-based Cosmos Planet Go App to simulate the motion of planets in the universe. This allowed students to understand the characteristics and features of each planet through its simulated motion in the universe. This study adopted a quasi-experimental method and the qualitative analysis to conduct experiments on teaching astronomy in an elementary school in central Taiwan. The control group students were taught using traditional classroom narrative teaching, and the experimental group students were taught using the AR-based Cosmos Planet Go App. The results showed that students who learned with the use of the AR-based Cosmos Planet Go App performed significantly better than the control students on measures of learning effectiveness, learning motivation, and flow experience. Moreover, learning engagement, which occurs when students can use multiple perspectives to solve problems, is the most important element for evaluating the AR-learning environment in creative situations. This study extended the research field of digital technology-assisted learning to the discussion of integrated creative learning environment, which can be used as the basis and reference for scholars' research.