To begin this tutorial draw a circle using the "Elipse Tool." Hold the shift key in to keep it perfectly round. I used 008AFF blue, but you can use any color you wish.
Now right click on the shape layer and select "Blending Options". Now click "Gradient Overlay ".
Don't click OK yet...Still more to do.
Now click on "Stroke."
Click OK.
Now create a new layer and create a selection as I have done below using the "Eliptical Marquee Tool." I also zoomed in for accuracy. Now click the "Gradient Tool" (making sure that white is the foreground color) and use the "Foreground to Transparent" gradient in the "Options Pallete." Start your gradient at the top of the selection and drag down to bottom. Hold the shift key while doing so to keep the gradient straight.
Pretty simple tutorial but a neat effect.
The Results!!!
More Tutorials: 
