I'm teaching an astronomy class in the fall and I had this idea for a photo project. I want my class to take a daily picture of the Sun (around sunrise) at the exact same location and having the camera pointing in the exact same direction. At the end of the class, I want to combine all the pictures of the Sun into one picture so they can see how the Sun has moved across the horizon over the school year.
My question is, what's the best camera (and setting) to do this with. I have access to an SLR, iphone, and ipad camera. After I have all the pictures, how do I go about merging them all? (In terms of what software woudl work and the basics of how to do it?)