Stars selection

Hi!

Along with Myra's great idea, you can also use a channel selection. If you open up your Channels panel and look at the individual channels, look for the channel that has the most information (I think it would be probably be the blue channel) and duplicate that channell. This will turn it into an Alpha Channel. Then select that duplicated channel and use the Curves Dialog to deepen the contrast of the image. You can also paint with black over everything you don't want to be part of the selection. Once you have isolated the stars that you want and everything else is black, you can go back to your Layers Panel and use Select>Load Selection to load the channel you just worked on, and it will select only the stars you want. Having a Alpha channel is a handy process especially if you need to make adjustment in the future.

Michelle

You might try using the Object Select Tool set to Lasso mode in the Options bar (Window > Options) and encircle the stars in the constellation. When you have the selection, you can add your Curves adjustment layer to have Photoshop automatically create the layer mask based on that selection. And you can modify your adjustment layer as desired.