Figure 3-24 Rotating Furnace for Making Parabolic Telescope Mirrors (a) To make each 8.4-m primary mirror for the Large Binocular Telescope II on Mount Graham in Arizona, 40,000 pounds of glass are loaded into a rotating furnace and heated to 1450 K (2150°F). This image shows glass fragments loaded into the cylindrical furnace. (b) After melting, spinning, and cooling, the mirror’s parabolic surface is ready for final smoothing and coating with a highly reflective material.