Changing Sceneries under Changing Skies: Virtual Archaeoastronomy with Stellarium

Abstract

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.