Typically a photographer doesn’t take a long exposure during the day; this makes sense. A long exposure, which is when the shutter is left open for an extended period of time, rather than a fraction of a second, will let in more light. The day time being when the sun is out, that means you would typically have a worthless, blown out exposure. That is, unless you had a little piece of equipment called a neutral density (or ND) filter, which reduces the intensity of the light entering the camera. These little pieces of glass can open a whole new world of photography to those who want to try it.
And if you do try it, you can get stunning pictures like Kevin got above. This thirty second exposure of the Air Force Memorial, during the middle of the day, while using an ND filter, looks like something from a dream. There are multiple features of this photo worth pointing out: the motion blur of the clouds; the fascinating play of light on the metal arms of the sculpture; and, of course, the color of the sky. Kevin says that the color is not from post processing and is simply how the light interacted with the filter glass. Truly an excellent photo; makes me want to go buy one of those filters and start playing!