Textured Sphere

Open up your background texture. With the select tool draw a cirle on the background and select Edit/Copy. Then open a new image about 1.5 times bigger than your background image and paste the selected image into the center as a new selection. Deselect it, Edit/Copy and Edit/Paste as New Image, then Reselect the sphere in your new image. The selected copy of the sphere will be use to make the lighting effects. Select the fill tool: Mode=none, tolerance=0, fill=sunburst gradient, options: vertical=75, horizontal=25, forground=white, background=black. Fill the selected sphere. Promote Image 2 (shadow) to a layer. Edit/Cut Image 1 (texture), then paste it as a new layer over Image1. Adjust the opacity of Image 2 until the texture and gradient are blended (about 50). Now adjust the brightness by 1 and contrast by 50, or whatever makes your image look good.

ANOTHER WAY TO BLEND WITHOUT LAYERS Select Image/Arithmetic and select the settings seen in the image below. Where image1=textured sphere and image2=shadow. Then adjust the Brightness/Contrast as needed (brightness by 10 and contrast by 50).