Using the same instrument, it?s possible to make the lowest half of the sphere looking a little lighter than the other one.

Create Microsoft Windows Vista Wallpaper in Photoshop CS

Create Microsoft Windows Vista Wallpaper in Photoshop CS

Fill 0% on the layers.
Blending Options-Gradient Overlay

Create Microsoft Windows Vista Wallpaper in Photoshop CS

Gradient?s
parameters:

Create Microsoft Windows Vista Wallpaper in Photoshop CS

Make three copies of the new created layer and apply Free Transform option again to make the copies smaller.

Create Microsoft Windows Vista Wallpaper in Photoshop CS