Enabling efficient exploration of large-scale virtual environments such as those simulating astrophysical environments is highly challenging. Astrophysical virtual worlds span exceptionally large spatial scales occupied mostly by empty space, and this makes it difficult for the user to comprehend the spatial context during exploratory navigation. Public exhibits, where novice users have little experience using complicated virtual navigation interfaces, pose additional challenges.To address these issues, we propose multi-touch techniques to deliver an effective interface to navigate the unique features of large-scale 3D environments such as astrophysical simulations. In this work, we carefully study conventional multi-touch methods and adapt them to the practical requirements of this application. A novel technique called the powersof-ten ladder is introduced to support efficient movement across huge spatial scales using multi-touch interactions. We also investigate user experiences with various multi-touch finger gestures on our prototype digital planetarium.