I worked on lesson 9, Making Selections, on the photoshop Lesson videos.
I started with duplicating the layer by double clicking and choosing duplicate layer, naming it sky and chasing the document to Rocks with Planet. So it duplicated in the other photo.
I the loaded the section of sky in its layer by command clicking over its thumbnail.
I the selected the stars layer and pressed command T and changed the Y value to -1000.
I then went and changed normal, in the layer panel, to screen.
I command clicked the thumbnail for mars. Then I went to the Select menu and chose inverse, which selected all but mars. Then I went to the bottom of the layer panel and chose Add Layer Mask.