how to calculate topographic shadows (not shaded relief)

I'm looking for an efficient way to calculate topographic shading. By this I mean calculating the shadow a mountain would cast given a sun position, not simply the normal angle of a pixel towards the sun. So I'm looking for something like los2.m instead of lightm.m. The roadblock with los2 is that it requires a lat/lon/elev for the light source, and the only solar calculators I can find return an azimuth/zenith. In the end what I want to do is ingest a geotiff DEM and then calculate mountain shadows for any day and time or year. It doesnt have to be exact, so convenient approximateions would likely be fine; it also has to work above the arctic circle. Any ideas would be appreciated.

[Raul Arribas]

Hi Matt,

Was wondering if you ended up being able to solve this problem?

Encountering a similar dilema myself, if you have any advice.

Thanks!