During cryogenic testing, engineers are visible in the reflection of the James Webb Space Telescope's 6.5-meter primary mirror, which consists of 18 hexagonal beryllium segments coated with a ~100 nm layer of gold. Gold was selected because of its high reflectance in the infrared portion of the electromagnetic spectrum, where Webb operates. By maximizing infrared throughput and minimizing optical losses, the mirror system provides the sensitivity required to detect extremely faint radiation from the earliest galaxies. Source: National Aeronautics and Space Administration. James Webb Space Telescope Mirrors. NASA, webb.nasa.gov/content/observatory/ote/mirrors/index.html. Want more interesting content like this ? Follow gravitonomy :) #jameswebbspacetelescope #jwst #science #space #astronomy