Thousands of people worked for almost two decades on construction and testing of the optical and science segment of the of NASA’sJames Webb Space Telescope. The segment is now completed, and the photo shows engineers conducting a white-light inspection of the mirror in one of the largest cleanrooms in the world, located at NASA’s Goddard Space Flight Center. The mirror itself is made of 18 gold-plated panels of beryllium.  The science instruments and electronics are located on the back of the mirror. The other two segments of the telescope include the reflective sunshield and the main chassis of the spacecraft that will carry the telescope into space.