STEP 1
Open new document in Photoshop with black background. Make sure, your foreground color is set to white and background is set to black.
STEP 2
Create new layer and select Elyptical Marquee Tool from the tool palette. Make circular selection anywhere in the middle of that new layer (holding down the SHIFT key will do a perfect circle)
STEP 3
Now it is important that you do this: go to Filter/Render/Clouds. Again Filter/Render/Difference clouds. You need to repeat this last step about 30x (press Ctrl+F 30 times) to get something like this:
STEP 4
Now apply this filter:
Filter/Stylize/Glowing Edges with these settings:
and you should get this:
STEP 5 - getting rid of white stroke
Note that your sphere might have a white stroke around its edges as a result of this effect. You can delete it using eraser or simply make new a little bit smaller circular selection around a sphere so that white stroke is outside new selection. Now go: Select/Inverse and press delete. This will get rid of white stroke.
STEP 6 - making the planet
Now we need to make it look 3D. Holding down Ctrl key, select the sphere layer. It makes the selection for you.
Go to: Filter/Distort/Spherize. The value is 100%. normal mode. It gives you this:
STEP 7 - colorising the sphere
Image/Adjustment/Hue-Saturation. You can make the planet any color you like. Make sure you de-activated selection. I made it green using these values:
to make it look like:
STEP 8 - lighting
We want to look it like it is set in front of some shining sun-like star. To do that go to Filter/Render/Lighting Effects and use these settings and light position depends where you decided to have the sun. Make it look natural:
to get this:
STEP 9 - sun
Before applying this, make sure you click on the black background layer. Simply apply lens flare in: Filters/Render/Lens Flare. Position and intensity depends on the light source used in last step. In my case I used this:
to get this:
STEP 10 - adding the glow
Last step is the green glow around the planet. Get back to your sphere layer and apply the outer glow(Layer/Layer Style/Outer Glow):
Note, that I selected the glow color - green. If your planet is red, make it red. DONE!
...and here we are:
