If you want to see how I made this (and how you can too!), visit my HDR Tutorial. I hope it gives you some new tricks!
There's this moment in California when the sun hits the horizon that I am quite sure most of the natives take for granted. The gradation of sky from the burning sun to the deep blues can only be really appreciated if you swing your head around and purge your short-term memory. The effect is not dissimilar to the optical illusion of the giant full moon on some evenings, seemingly magnified by our inability to establish a frame of reference. I think something along those lines happens with color as the sun dips. You can see this from space, as the sudden band from light to dark rips around the earth -- that same viewing cone can be seen from anywhere on the surface, and it can be best noticed in places like LA, with the nearly infinite horizon.