From space, the James Webb Space Telescope (JWST) resembles a giant sunflower perched on a silver "surfboard" sunshield, safeguarding it from solar heat and glare. Its 18 gold-coated beryllium hexagonal segments form a primary mirror over 6 meters wide. But why gold?
A collaboration between NASA, the European Space Agency, and the Canadian Space Agency, the JWST was set to launch by December 24 at the latest. Once deployed, it became the most powerful observatory ever sent into space. The key to its extraordinary infrared vision? A vast golden primary mirror designed to capture maximum light from the universe's most distant objects.
Measuring 6.5 meters in diameter, the JWST's primary mirror dwarfs the Hubble Space Telescope's 2.4-meter one. Composed of 18 interlocking hexagonal segments, this design maximizes light collection without gaps.
As NASA explains, "If the segments were perfectly circular, there would be spaces between them." A near-circular hexagonal shape concentrates light efficiently onto detectors, avoiding distortions from oval or square alternatives.
Each segment features six actuators on its back, enabling precise adjustments by mission engineers to perfect the telescope's focus.
Beyond its size and shape, the mirror's gold coating delivers exceptional performance. Gold provides the highest reflectivity across a broad spectrum of infrared wavelengths, essential for the JWST's mission.
The coating achieves about 98% reflectivity, reflecting nearly all incoming photons—a benchmark that's extraordinarily hard to surpass. While gold-coated, the segments are made from lightweight beryllium for structural integrity. Each weighs roughly 20 kg on Earth, remains rigid, and withstands cryogenic temperatures down to -220°C.
