This paper describes an ongoing research comparing two 3D astronomical tangible models: an Augmented Reality model versus a physical model. According to IBSE principles, learners should investigate and manipulate in order to become conscious of the origin of astronomical phenomena, construct scientific knowledge and change their misconceptions. In primary French schools, physical models are usually used. However, children do not take advantage of these models and form new synthetic models instead of scientific ones. We aim at providing an adapted pedagogical environment support. An Augmented Reality environment was designed for inquiry-based learning. This tangible AR model shows augmented views of the celestial bodies and supports the pupils' investigations using spatial visual guides and views from a terrestrial observer. The AR model not only exposes the phenomena as in several Virtual Environments, but also allows pupils to virtually move the celestial bodies and test "as for real" their hypotheses. Our results show that the AR environment is particularly suitable for astronomy learning compared to the physical one. Only AR users have developed scientific conceptions of the explored astronomical phenomena and learnings have been significantly improved. Furthermore, we present some arguments in order to support the assumption that the AR model assists the process of scaffolding and motivation dynamic by enhancing task controllability and by promoting collaborative learning.