Scaled the earth and work it so that his head was in front and his hands were behind. Then I use the Dodge and Burn tools to make the shadows work (sort of)
step 3 of 3
Filled the background with black. Both the source pics had black backgrounds originally but black is not always black so I used a solid background to make them match. Used a simple lens flare to make the sun and added a few stars on a separate layer. Blured the stars just a touch.