If you've never thought to find out why aperture works the way it does, you should definitely check out this simple explanation of optics, aperture and pinholes by MinutePhysics.
Andy Adams of FlakPhoto has an interesting new digital exhibition titled Looking at the Land — 21st Century American Views that features 88 landscape photographs captured around the United States since 2000. What's neat is that each of the images is accompanied by an explanation of "why" it exists. Adams asked each of the photographers the same questions, with the main one being, "Why did you photograph this place?"