The primary mirror is 7.9 feet (2.4 meters) in diameter, while the secondary mirror is only 12 inches (30.5 centimeters) wide. The size of the primary mirror allows it to collect 40,000 times more light than the human eye, meaning that Hubble could see the landing lights of an airplane over San Francisco from Washington, D.C. Though the primary mirror is large, its design makes it as lightweight as possible. Instead of a solid core, Hubble’s primary mirror has a honeycomb interior, reducing its weight from about 8,000 pounds (3,636 kg) to 1,800 pounds (818 kg). Both the primary and secondary mirrors are made of a high-silicon, Ultra-Low Expansion Glass developed by Corning Glass Works.