Learning astronomy at higher level can be both exciting and challenging. Entering the discipline of astronomy involves learning the way that astronomers communicate knowledge, using a multitude of disciplinary specific semiotic recourses to understand the multidimensional universe. A new-to-the-discipline student will need to learn to “read” and “write” all these resources in her endeavour to learn astronomy and become part of the discipline. In this paper, we present a study where university students and professors are presented by different 2D and pseudo-3D resources—representations of astronomical objects—and asked about how these objects may look in 3D, i.e. we ask them to extrapolate three-dimensionality from 2D inputs. These inputs are 2D pictorial representation and world-class 3D rotating volumetric models presented on flat screens. Data were collected using a web-based questionnaire from 53 participants in four different countries. From the results, we find that all participants struggle to find cues for depth perception in the 2D pictorial representations. As could be expected, the student participants were much worse in doing so than the astronomers, but with one exception: students used the offered motion parallax as their main cue when this was available. The astronomers used many cues in their struggle to perceive depth but surprisingly did not use the presented parallax motion to a large extent. We interpret this as follows: for the students, they lack the knowledge to use disciplinary cues and used the only cue that they know from experience, namely, parallax motion. For the astronomers, they used a multitude of disciplinary cues based on their extensive disciplinary knowledge, and did not find the new cue, motion parallax, as useful as the ones that they were used to use. In this paper, we present and discuss these results and its implication for teaching astronomy.