In this application, the star is not used to correct for the rotation of the Earth, but to correct for turbulence in the Earth's atmosphere. By measuring the observed motion of the guide star, and making minute distortions to the primary mirror, the telescope can produce images with much greater sharpness than is possible without adaptive optics. However, only about 1 percent of the night sky is close enough to a natural guide star to use adaptive optics, so various methods to create artificial laser guide stars have been developed, including the sodium laser system developed by the Lawrence Livermore National Laboratory and used by the University of California's Lick and Keck observatories.[2]