(Jury duty lasted until mid-December as predicted. I've been busy with the holidays and playing catch-up.)
We've all heard the term "optical illusion", but what is that exactly? Well, in simple terms, it is when the visual process makes you see something as it really isn't. The visual process involves not only your eyes, but also your brain. The brain is the part that becomes involved with the illusion, interpreting the image produced by your eye the way it wants it to look, not how it really looks.
The most common optical illusion we encounter each day is looking up at buildings. When you take a picture of buildings, particularly tall ones, you see distortion and convergence of walls. When you look at the same building, those walls are straight all the way to the top. Which one is the optical illusion? It's your live view of a straight building.
Your brain knows that the building is straight (unless it's the Luxor in Vegas), so it takes the image sent from the eye and changes it. Your camera on the other hand, shows you how it really is. If you could look at the image on the retina of your eye you would see the same thing that you see in the photo made by the camera—converging lines. Our brains can't handle that, so when we look at the building it is made straight—an optical illusion. It's no secret that things look smaller and smaller the farther away they get but the brain is more comfortable making things look familiar regardless of distance. You can see the same thing happen to a lesser extent when you look down a road or train tracks.
Another common optical illusion is the moon (or sun) looking huge when at or near the horizon (no, that is not a product of atmospheric interaction). The reason this happens is not as well understood as the building example. The most reasonable explanation is that, because our brain knows the sun and moon are really big, when you see them near the distant horizon with its tiny features the brain magnifies the celestial object to keep that perspective understandable.
If you think the atmosphere is what's really causing that magnification and it's not an optical illusion, here's what you can do to put that to rest. Next time there's a moonrise or sunset, set your camera's lens to the equivalent of a "normal" lens on a 35mm camera (a focal length of around 50mm). This gives the same field of view that you have when you are looking at something. Take a picture of the sun or moon and look at the photo. The sun or moon that covered half the horizon when you looked at it with your eyes looks no bigger in the photo than it would if you took a picture of it when it's overhead. The camera shows you unmolested reality.
So, next time you see a photo with straight buildings or a giant moon in the sky over a night cityscape, you'll know that the photo has had some work done. Perspective control lenses can take care of the buildings and digital editing can be used for either situation.