Place a new layer beneath the earth layer for adding a background (star field)
Select the white background on the Earth layer, expand the selection to include the black outline of the Earth. Delete to erase all the background and Deselect.
Add outer glow layer style to earth layer and then Create layer so that the glow can be modified.
Lock the transparency of the outer glow layer, then paint and mask to sculpt the lighting.
Add a new layer in Overlay mode and link to the Earth layer. Brush in shadows and highlights for 3-d effect.

forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=34265891

image posted by Alex: