:: Step 1.

In photoshop open up a new image sized 350×350 px, and fill it with black color.

 :: Step 2.

Create a new layer, choose a Brush tool and make a few white dots, here and there, different sizes, like on the photo below. (Name that layer "stars")

 :: Step 3.

Now double click on your "stars" layer, check only "Outer Glow" checkbox and enter the settings for glow, like on the picture below.

 :: Step 4.

Create a new layer (name it "clouds"). Change your foreground color to this: #bff8ff, then change your background color to this: #002040.

 :: Step 5.

Now go to Filter -> Render -> Clouds. Change a blending mode for layer "clouds" to Hard Light. like on the picture below.

 :: Step 6.

Now your got something like this:

 :: Step 6.

Change now your foreground color to #eaff5b. Create a new layer on top of Background layer. Use your Brush tool and fill some spaces with that color, like we did below:

 :: Step 7.

Next, go to Filter -> Blur -> Gaussian Blur -> for radius enter 54 pixels. Click on OK. Then change the blending mode for that layer you just painted, from normal to "Pin Light" and you are done.

 :: Final result: