Moon glow - how do I get rid of that square around the moon?

You’d want to use a texture mask in the material. Set the material shading to masked. For the mask you’ll want an image like the moon but instead of the moon just a solid white circle, and black in the areas you don’t want to show.

Thank you so much for your reply. I kind of got the idea. How do I go about doing that? I’m extremely new to all this. Sorry the inconvenience.