STEP 1: Create a New Layer and using the circle selection tool AND holding shift down (THIS MAKES IT A PERFECT CIRCLE) pick a medium blue colour and using the paint bucket, FILL the circle

STEP 2: Select a large sized airbrush (I used 200) pick a dark colour and shade around the edge of your circle half inside the selection, half outside.

STEP 3: Build up using smaller brush sizes to define the edges more, with more emphasis on the bottom right hand edge, because the light is coming from the top left in this picture. Now add a small blob of white as shown and using a larger brush size add another dab of white on top, but less opaque!!!!! .

STEP 4:Now create another layer between the background and the sphere as shown in red. Using the circle selection tool again, select an oval where you think the shadow would be cast by the sphere. Now go to SELECT/FEATHER and set it to about 10 pixels, this blurs your selection, fill it using a dark colour and as you can see you have a shadow, this helps the sphere to sit on the surface better.

STEP 5: Now use CTRL and left-click to select the sphere layer, shown in red, this will select the sphere! Now using the freehand lasso tool shown above in red and holding down ALT, draw a wavy line across the sphere and loosely around the outside top of the selection, this will minus the top half of the selection away, leaving the the bottom selected as shown, now go to SELECT/MODIFY/CONTRACT and contract by about 2-5 pixels, this brings the selection inwards slightly, Now airbrush along the top edge of the selection to define an imaginary horizon being reflected.

STEP 6: Hold CTRL and click the sphere layer to select the full sphere again, now go to SELECT/MODIFY/CONTRACT and contract by 1 pixel, go to SELECT/INVERSE and press delete on your keyboard, this will clear 1 pixel all the way round the sphere so that when you add a background, you wont get a white fringe around the sphere. Now click the background layer as shown in red, select the top half (using the rectangle selection tool) and fill it with a light colour, go to SELECT/INVERSE and fill the bottom half with a darker colour, airbrush a bit of variation around the edges if you want to!!!!

STEP 7:You should end up with something like this, Its quite simple but the ideas and methods used to create this are used in almost everything I do, so have a go! I hope you found this useful. Oh Yeah, One final TIP: pressing CAPS LOCK toggles your brush size cursor on and off, I prefer it on to see where the virtual paint is going to hit :)