Why is Webb optimized for near- and mid-infrared light?
The primary goals of Webb are to study galaxy, star and planet formation in the Universe. To see the very first stars and galaxies form in the early Universe, we have to look deep into space to look back in time (because it takes light time to travel from there to here, the farther out we look, the further we look back in time). The Universe is expanding, and therefore the farther we look, the faster objects are moving away from us, redshifting the light. Redshift means that light that is emitted as ultraviolet or visible light is shifted more and more to redder wavelengths, into the near- and mid-infrared part of the light spectrum for very high redshifts. Therefore, to study the earliest star formation in the Universe, we have to observe infrared light and use a telescope and instruments optimized for this light. Star and planet formation in the local Universe takes place in the centers of dense, dusty clouds, obscured from our eyes at normal visible wavelengths. Near-infrared light,
