Click in the left side of the 'New Layer' section of the Layers panel to make the eye reappear.
The white new layer reappears, paste the rectangle of light pollution into it (Ctrl-V). Apply a
Gaussian blur (Filters-blur), set to about 25 pixels. Ignore the 'Floating Selection (Pasted Layer)
message in the Layers panel. You can make it go away by clicking anywhere in the white space
around the light pollution box in the new layer, which you'll be doing anyway in a bit.