Select the sky with the magic wand with tolerance set to about 5. Then clean up the edges of the plane with the lasso tool.
Select the colour of blue of your choice as the foreground colour, with white as the background, then filter >render > clouds
Then make a rough selection towards the outside of the image, feather the selection (I chose 25 px but that depends on the sise of your image) then use levels to darken the edges of the image
