Working on Hubble's Main Mirror (1990) Workers study Hubble’s main, eight-foot (2.4 m) mirror. Hubble, like all telescopes, plays a kind of pinball game with light to force it to go where scientists need it to go. When light enters Hubble, it reflects off the main mirror and strikes a second, smaller mirror. The light bounces back again, this time through a two-foot (0.6 m) hole in the center of the main mirror, beyond which Hubble’s science instruments wait to capture it. In this photo, the hole is covered up.