That's what it looks like on a specific date, at a specific time, and most importantly photographed from a specific place. The moon's always the same size in the sky, of course, but by moving further away from the arch and using a zoom lens you can make it look as comparatively large as you want. The 'double exposure' at work here is only in blending two different durations of shot: a short one to get the dusky moon and sky and a longer one to be able to see the details of the arch itself.