Astronomy Picture of the Day . ... Credit: P. Stomski ( W. M. Keck Observatory ), Caltech , U. California Explanation: In buildings eight stories tall rest mirrors ten meters across that are slowly allowing humanity to map the universe. Alone, each is the world's largest optical telescope : Keck . ... Since opening in 1992 , the real power of Keck I (left) has been in its enormous light-gathering ability - allowing astronomers to study faint and distant objects in our Galaxy and the universe . ...