Another example.
We have same night and stars... Rain and moon...
Ok, add some more 'realism' - add flare to moon and change it when rain is on.
Code:

...
sky moon {										//moon
	type=<bmoon.tga>;
	flags=visible,transparent;//,transparent,overlay;
	alpha=100;
	x=500; //play with this and all below
	y=-130;
	z=100;
	scale_x=0.25;
	scale_y=0.25;
	scale_z=0.25;
	layer=5;
}
sky moon_flare {										//moon
	type=<bmoonflare.tga>;
	flags=visible,transparent;
	alpha=100;
	x=500; //pos to moon
	y=-130;
	z=110;
	layer=10;
}
...
//somewhere in your code
...
	while(1) {
		while(RAIN==on) {
//your rain code here
...
			if (moon.alpha > 50) { moon.alpha-=time; }
			moon.alpha = max(moon.alpha,0); 
			if (moon_flare.alpha > 50) { moon_flare.alpha-=time; }
			moon_flare.alpha = max(moon_flare.alpha,0); 
			wait(1);
		}
		if (moon.alpha < 100) { moon.alpha+=time;	}
		moon.alpha = min(moon.alpha,100); 
		if (moon_flare.alpha < 100) { moon_flare.alpha+=time;	}
		moon_flare.alpha = min(moon_flare.alpha,100); 
		wait(1);
  }

What is this ?
When rain is on - flare around moon slightly 'muted'.
Try, you'll like it

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