What is the James Webb Space Telescope?
21 Sep 2009





The JWST Team in front of a lifesize model of JWST


​​​​The James Webb Space Telescope (JWST) was originally commissioned by NASA in the mid-to-late 90s as the replacement for the Hubble telescope, one of the most well know and successful space science missions ever undertaken. Hubble has become a household name, its amazing images seen across the globe inspiring minds both young and old to take an interest in our universe. Hubble has also done some truly groundbreaking science like the imaging of super-novas, discovering a super-massive black hole, and discovering that planetary nebulae (like snowflakes) are never the same twice. So NASA decided that they’d need a replacement to carry on the flagship science once Hubble reaches the end of it's useful life.

One of the main components of a space observatory, such as Hubble or JWST, is the primary mirror. This sets how much light can be collected and condensed down to fall on the instruments. JWST will have a 6.5m primary mirror - over 4 times bigger than Hubble's which will make JWST many times more sensitive and more powerful to look at the very faint and very far distant objects in the universe.

Hubble is working mostly in the visible spectrum but also has some instruments working in near infra-red; the part of the infra-red region that is closest to visible light, and also instruments in the near ultra-violet region.

Hubble Deep Field image  
Hubble Deep Field


Because of the results that Hubble (and ground based observatories) have generated since Hubble was designed it is clear that large amounts of scientific knowledge can be gained from more detailed observations in the infra-red part of the spectrum. For this reason JWST has been designed to operate exclusively in the infra-red part of the spectrum.

Infra-red radiation is given off both by relatively cold objects, things that aren’t as hot as stars and so not emitting light in the visible spectrum, but also by things that are very far away. We can only see these far away objects with infra-red because of an effect called red shift, these objects are retreating from us because the universe is expanding, and the light from them is shifting to the red part of the spectrum.

This red shift (or Doppler shift) is similar to the effect that you hear when a police car or ambulance is coming towards you and the sound gets higher, and then as it passes you and it moves away the tone drops.​

For more information please contact: RAL Space Enquiries