Another way to describe this.
And this is a fantastic photo:
If it was a close to instant "snapshot" the lights on the bridge would be extremely sharp and you would likely see "rough detail in the clouds" (think 1/400sec) <--semi-realistic number
at perhaps 1/4sec or maybe even 1/2sec you would see the blurring( soft glow) of those same lights, and a very smooth texture of the cloudbank. (thats what we see)
At several minutes or more you would notice that the moon moves fairly quickly across the horizon, and would not appear as sharp as it is in the photo.
(these numbers are made up, because I have no way of telling what amount of light was available, or the apeture of the lens, etc, or the fact that I honestly dont know the math to figure it out anyways)
But in laymens terms, this is kinda how it works