A powerful green laser is useful in astronomy for pointing at objects easily. You center a known object in your telescope, then aim the laser (there are mounts to attach to your telescope) at the object. The beam appears to reach the stars. When you want to look at another object, simply turn the laser on and move your telescope so the laser points at the desired object, turn it off, and observe or photograph.
it can also used to point any object with your gun and to feel like spec agent)