Why are the laser beams visible?
While observing in the thin, clear air on a cold, dry mountaintop, there must be very little dust and mist floating in the air to scatter the light so an observer standing to one side can see it. Is the scattering caused by aerosols floating in the beam, or by the molecules of air itself? Also, how bright are those beams? Are they as visually dramatic as they appear in the photographs, or are they just over-exposed?