1. Make a new file, Width:800 Height:600.
2. Press "d" on your keyboard, this resets your color pallete. Make a new layer, and color it black.
3. Go to Filter>Texture>Grain. Make the Grain Type Sprinkles, Intensity:1, Contrast:100.

4. On the same layer, go to Filter>Blur>Gaussian Blur. Make the Radius 0.3.
This gives it the star feel, rather than some random dots.
5. Now, keep that document open, but go to File, and create a new document. Width:500 Height:500.

6. Create a new layer in your 500x500 document. Go to Filter>Render>Clouds.
7. Go to Image>Adjustment>Hue Saturation (or press Ctrl+u, for windows).
Use the following settings:

8. Go to Filter>Blur>Motion Blur.
Use the following settings:

9. Now, Select your
Elliptical Marquee tool. (Click Elliptical Marquee if your confused)
10. Begin to make a selection of your effect, try to select as much of the image as possible, when you think you have it, continue holding your selection, but then hold shift. This causes your selection to become a perfect circle. It should end up like the following:

11. Go to Filter>Distort>Spherize. Make the amount 100. After you've done that, repeat. (Or press CTRl+f, for windows users)

12. While still in your selection, go up to Edit, then Copy.
13. Open the document with the stars, and paste your planet.
You should have something like this so far:

14. Drag your planet layer into the New Layer button, this should duplicate your planet layer, and leave you with one planet overtop of another.

15. Your layers should go something like this now:
Layer 2 Copy
Layer 2
Layer 1
Background.
Click "Layer 2", and go to Filter>Blue>Guassian Blur.
Notice in my screenshot, the blur adds a bit of glow to the planet.

That should be about all you need to know...
Final image result (with some added text ;P):