Webb’s Mirrors

The James Webb Space Telescope uses two mirrors to perform science operations.

The telescope’s primary mirror is made of 18 hexagonal-shaped mirror segments, each 1.32 metres in diameter and weighing approximately 20 kilograms. The total diameter of Webb’s primary mirror spans 6.5 metres, which is so large that it has to be carefully folded into the rocket’s fairing for launch. Each of the telescope's mirrors is covered in a microscopically thin layer of gold, which optimises them for reflecting infrared light – the primary wavelength of light this telescope will observe. 

The telescope also hosts a convex secondary mirror that is roughly 0.74 metres in diameter. This is the second surface the light from the cosmos hits on its route into the telescope.