Virtual reality (VR) learning environments can provide students with concepts of the simulated phenomena, but users are not allowed to interact with real elements. Conversely, augmented reality (AR) learning environments blend real-world environments so AR could enhance the effects of computer simulation and promote students' realistic experience. However, AR-based learning environments had a lot of dynamic real objects which may increase learners' mental effort. Moreover, paucity of research compared AR with VR and other mature technologies. Thus, the aim of this study is to compare the influence of the 2D image-based VR and AR in an inquiry-based astronomy course. The findings of this study suggested that the real objects presented in the AR system could reduce the mental load because students could take the real objects of the AR system as the reference objects of the movement of the moon. Furthermore, the sense of the immediacy is increased due to the fact that peers appear on the AR system. Accordingly, the real objects and the sense of the immediacy not only enhance the learning motivations, but also encourage the students to keep conducting the tasks.