Assign nodes to a specific area of the rendered image (compositor)

Question

i am doing a scene at night with a selfmade world with stars. In my final render i want to now add a glare node in the compositor. My problem is that i have other lightemitting sources which are also affected by the glare node. Is there a way to assign this glarenode only to the top part of the rendered image (which is where you would see the nightsky)?

Answer 1

yes, you can e.g. with this node setup:

as you can see, on the top is with glare, the bottom half without.