I am a cognitive psychologist investigating the moon illusion (the moon looks much larger on the horizon than high in the sky). In an experiment I am planning, I ask people to judge the orientation of the moon relative to the horizon. To see how well people can do the task, I need a way of knowing the true relative orientation of the moon. Using SkySafari 5 on my Mac, I can generate an image of the moon and can compute the relative orientation (compared to some arbitrarily defined standard orientation). However, my method is clumsy and I wonder if there is some algorithm that can provide the needed information more directly. Also, I wonder in general how much I should trust the images generated by SkySafari5 with regard to the perceived orientation of the moon.
Any advice would be welcome.