Noise elimination

Noise shows up mostly in the shadows or very dark areas of an image.  If you are forced to use a high ISO and the picture has a lot of dark sky in it, instead of applying noise software (such as Nik's Define 2.0 or Topaz DeNoise 6) to the entire image, select the sky, feather the edge of the selection with Select > modify > feather (about 5 pixels), and then apply the noise reducing software only to the sky.  I suggest this because these software programs tend to reduce sharpness.  If the sharpness of the sky is reduced, you mostly likely won't notice it. This is Notre Dame Cathedral in Paris.  I placed the moon behind the architecture with Photoshop.