Result:
Open a new document, about 300x300 with a white background.
Create a new layer
Get the Elliptical Marquee Tool and draw a circle a decent size
Get the Gradient Tool.
Use these settings :
Drag the gradient so that the black part is on the bottom.
Create a new layer
Now goto Edit > Stroke and use these settings:
Press Ctrl+D to deselect.
Goto Layer > Layer Style > Gradient Overlay and use these settings:
Create a new layer, then grab the Elliptical Marquee Tool and make a selection like this :
Grab the Gradient Tool again, and set your colors to default by pressing D, then switch your foreground and background by pressing X.
Now, drag the gradient so you have the white part on the top.
Create a new layer.
Now with the Pen Tool make a selection like this:
Now grab the Convert Point Tool and move the anchor points until you get something similar to this:
Now click on the Path tab.
Right Click on the "work path" and choose Make Selection.
Right click on it again and select Fill path..., and use these settings:
Reset your colors by pressing D.
Right click on the Work Path again and choose Delete Path.
Go back to the Layers Palette, and Ctrl+Click on the orb layer that you created.
Press Ctrl+Shift+I to select the inverse of it and press Delete.
Press Ctrl+D to deselect.
Here is the end result:
