A major topic in archaeoastronomy is the orientation of human-made monuments with respect to the surrounding terrestrial and celestial landscape. There are many examples of temples oriented towards sunrise on solstices or other culturally important dates, and the orientations of many more structures are under discussion, concerning relations to the Sun, Moon, planets and even some of the brightest stars. Time and geographical coordinates are the key parameters from which the celestial view is computed with a desktop planetarium program. Developments in the popular open-source project Stellarium in recent years were particularly directed towards enhancing its applicability for archaeoastronomical research. Stellarium can display a calibrated panorama horizon which enables a virtual observer to embed himself in one particular viewpoint. With an optional extension it is even possible to load 3D scenery, usually a combination of terrain and virtual reconstruction of the monument in question. A researcher can walk around in this virtual world and observe along monument axes, building edges, or even patches of sunlight as they may have been visible falling through holes in a wall centuries ago. A problem for most 3D virtual reconstructions of archaeological monuments is that they show a static snapshot of a landscape as it may have looked like at a certain point in time. Showing the next ``monument phase’’ requires loading a new file, which distracts the observer. With archaeoastronomically significant directions slowly changing over centuries, we also should not show the monument under an astronomically wrong sky. The most recent change in Stellarium’s 3D mode allows temporal changes not only in the sky but also in in the 3D scenery. Parts of the model which do not fit the simulated time can be hidden by transparency, which also allows for modelling temporal uncertainty. Relevance for the conference: Simple and accurate simulation of the astronomical orientation of archaeological monuments can be important both for research and outreach. Relevance for the session: The 3D simulation of monuments under the skies of past times for archaeoastronomy research can now display temporal changes not only in the sky but in the monuments themselves. Innovation: A simple rendering trick allows showing temporally changing parts of monuments in an archaeoastronomical simulation environment. References: • Georg Zotti. Archaeoastronomical simulations in a desktop planetarium. In Wolfgang Börner, editor, CHNT20: Conference on Cultural Heritage and New Technologies, Proceedings CHNT2015, volume 20. Stadtarchäologie Wien, October 2016. • Georg Zotti, Florian Schaukowitsch, and Michael Wimmer. Beyond 3D Models: Simulation of Phased Models in Stellarium. In Proceedings of the 2017 SEAC Conference, To Appear.