(Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Vienna, Austria)

Keywords: virtual reconstruction, desktop planetarium, archaeoastronomy, astronomical orientation studies

It is well-known that many prehistorical and historical building structures (e.g. the Pyramids of Giza and several temples in Egypt, Stonehenge, Newgrange, India, or Mesoamerica) have been erected following astronomical orientation patterns.
A powerful way to identify and analyze, and also to demonstrate astronomical orientation patterns in archaeological structures is the use of accurately georeferenced virtual reconstructions of past architecture in a virtual environment capable of accurate astronomical simulation.
There are architectural simulations and game engines which include simple sunlight models and even real-time shadows to simulate appearance in the present era, but the slight difference in ecliptic obliquity centuries ago is usually not covered, and the night sky usually is not properly depicted at all. Accurately computed solar positions usually require expensive custom developments.
On the other hand, visually convincing and astronomically accurate desktop planetarium programs so far could at most load a photographic (or artificially rendered) horizon panorama of a single standpoint to be used as foreground in visual analysis of temple axes or other possibly important sightlines, so that analysis of temple axes can require lots of such panoramas to be prepared with other programs.
During the ASTROSIM project (2008-12), the author had initiated development of a plugin prototype for the popular free and open-source desktop planetarium Stellarium to simulate the potential astronomical use of certain prehistoric monumental buildings on a high-end graphics PC. This plugin enables researchers to load a properly oriented virtual environment (e.g. temple with surrounding landscape) into an astronomical simulation environment and explore it in a virtual walkthrough fashion to combine architectural and celestial simulation, including real-time shadows. The plugin has recently been greatly refurbished and has now been integrated in the regular distribution of Stellarium.