# James Webb Telescope How the James Webb Space Telescope's 18 gold\-coated mirror segments, five\-layer sunshield and folded launch configuration work together to see distant starlight\. By PETE\! Topic: Space [Open the interactive Jig](https://ask.jig.com/j/m0HGwI3m3sHd) ## Transcript ### 1. A golden eye on the cold side This is the James Webb Space Telescope, the largest telescope ever sent into space\. A golden mirror wider than a giraffe is tall gathers faint starlight, while a sunshield the size of a tennis court keeps it in deep shade\. Drag anywhere to turn it around\. Webb launched on 25 December 2021 and works about 1\.5 million kilometres from Earth\. ### 2. Eighteen golden mirrors The primary mirror is 6\.5 metres across and made of 18 hexagons, with a gap in the middle where light passes through\. Each segment is beryllium coated with a film of gold only 100 nanometres thin\. Motors behind every segment nudge it until all 18 act as one mirror\. Each segment has seven actuators: six to position it and one to bend its curve\. The whole mirror is aligned to about 10 nanometres\. ### 3. Folded to fit a rocket Webb was too big to launch open, so it flew folded inside an Ariane 5 nose cone 4\.6 metres wide\. In space it unfolded step by step: solar array, tower, sunshield pallets, booms, the five tensioned layers, the secondary mirror tripod and finally the two mirror wings\. The real deployment took about two weeks\. Here it runs in twelve seconds\. ### 4. Five layers of shade The sunshield is five separate sheets of Kapton, each about as thin as a human hair, with vacuum gaps between them\. Each layer reflects heat and passes less of it to the next\. Switch on the heat view to see the warm Sun side fade to the cold telescope side\. The telescope side stays below about 50 kelvin, colder than minus 223 degrees Celsius\. The MIRI camera is cooled further, to about 6 kelvin\. ### 5. The path of starlight Follow the light\. Starlight bounces off the big primary mirror to the small convex secondary mirror held out on three struts\. The secondary sends it back through the hole in the middle, into the instrument module behind the mirror, where more mirrors and four science instruments split and measure it\. Webb sees infrared light, from about 0\.6 to 28 micrometres\. Its colourful pictures translate those invisible wavelengths into colours we can see\. ### 6. The warm side Below the shield, in sunshine, sits the spacecraft bus at about room temperature\. It carries the computers, steering and fuel\. The solar array faces the Sun for power, and the antenna sends pictures home to Earth's Deep Space Network dishes\. The tower between the bus and the telescope keeps warm parts away from the cold optics\. ### 7. A million miles from home Webb circles a point in space called L2, about 1\.5 million kilometres beyond Earth, four times farther than the Moon\. From there the Sun, Earth and Moon always sit on the same side, so one shield can block all three while the mirror looks out at the cold, dark sky\. From L2 Earth shows mostly its night side, a thin bright crescent beside the Sun\.