What type of light does JWST primarily observe?

JWST primarily observes infrared light. Its instruments are designed to detect wavelengths from about 0.6 to 28.5 micrometres, covering long-wavelength visible light through the near- and mid-infrared.

Infrared astronomy helps Webb study exceptionally distant objects because cosmic expansion stretches their light toward longer wavelengths, a process called redshift. Webb can therefore examine some of the earliest galaxies and stars in the universe. Infrared wavelengths also pass more effectively through clouds of dust than visible light, revealing star-forming regions and otherwise hidden objects.

Webb is not completely blind to visible light: its shortest-wavelength coverage reaches into the red-orange part of the visible spectrum. However, it is fundamentally an infrared observatory, unlike Hubble, which has broader coverage across ultraviolet, visible, and near-infrared light.

Keeping Webb cold is essential. The telescope itself emits infrared radiation, so its five-layer sunshield blocks heat from the Sun, Earth, and Moon and helps prevent the observatory from overwhelming its own sensitive detectors.