I then use the magic wand with Tolerance set to 10 and select on a black area only. You should see the marquee that looks some thing like Fig. This will remove all the black from this layer and un select it. Contrast to 0. This layer will be the stars that are furthest away.
Snow plug in that is free.
I set the amount to 1 and apply it. I then use the wand as I did with the noise layer and clear the black. I do not however brighten this layer. You can adjust the opacity of these 2 layers to get the amount of density you prefer. To add dust I like to use one of the cloud filters I have.