definition of horizon in alt, az coordinate system

Question

I have a problem in which the observer can be far above sea level. Given RA and Dec, I am trying to determine altitude and azimuth for this observer and this target. I am using Observer() for the observer, and FixedBody() for the target.

Is the horizon that pyephem assumes for calculating altitude the actual Earth horizon (which is at a zenith greater than 90° for an observer far above sea level)? Or is it the horizon which is the local tangent drawn at the observer's location above sea level? It seems to be the latter from a few tests, but I would like to confirm this.

Answer 1

When someone visits a town at, say, 2500m above sea level, then the land around the town is usually also at nearly the same altitude, so, yes, the horizon is still at 90 degrees from the zenith. The horizon, in other words, "travels with you" since you are standing on land at a higher altitude. Your situation sounds similar enough to the following Stack Overflow question that the answer I put together there might work for you as well:

Results for Observer() seemingly not accounting for elevation effects in PyEphem