Question

3) The James Webb Space Telescop (JWST) of 6.5 m it will observe mostly visible and infrared radiation with wavelengths as small as 0.6 jam (micro- meters). It also has a massive Sun shield and elaborate cooling system to keep the detecting instruments below 50 K. Why must JWST be so cold? will be the successor to Hubble. With a primary mirror diameter

Answer 1

Being an exquisitely sensitive infrared astronomical observatory, the James Webb Space Telescope's optics and scientific instruments need to be cold to suppress infrared background "noise." Moreover, the detectors inside each scientific instrument, that convert infrared light signals into electrical signals for processing into images, need to be cold to work just right. Typically, the longer the wavelength of infrared light, the colder the detector needs to be to do this conversion while also limiting the generation of random "noise" electrons.

some of scientific instruments "see" both the reddest of visible light as well as near-infrared light (light with wavelengths from 0.6 microns to 5 microns). which work ideally at 37 kelvin so that's why also JWST need to be so cold.