Webb will be able to measure light wavelengths from 0.6 to 28.5 micrometers. The capabilities of the individual instruments are:
- Near-Infrared Camera (NIRCam): 0.6–5 micrometers
- Near-Infrared Spectrograph (NIRSpec): 0.7–5 micrometers
- Mid-Infrared Instrument (MIRI): 5–28.5 micrometers
- Near-Infrared Imager and Slitless Spectrograph (FGS/NIRISS): 0.6–5 micrometers
Infrared radiation cannot be seen with the human eye, though it is emitted by all matter other than dark matter. Using infrared astronomy, we can see details in the universe and determine the composition of distant objects, from exoplanets to galaxies.
Webb will undergo science and calibration testing once it reaches its orbit, so regular science operations and the best images will begin to arrive around six months after launch. However, it is normal to also take a series of "first light" images that may arrive slightly earlier.
As a NASA mission, all data from Webb will be publicly available online.
Webb will study both the far and near universe. Astronomers will use it to see infrared light emanating from planets and objects in our solar system, exoplanets, star clusters, nebulae, other galaxies, and the most distant reaches in the universe.
Webb has a limiting sensitivity of ~11 nJy, which means we can see objects of 25th magnitude at near-infrared wavelengths and 22nd to 23rd magnitude objects at mid-infrared wavelengths. This means that Webb can see things that are over 2.5 million times fainter than the faintest thing you can see with your eye.
Webb will be able to observe galaxies that formed about 400 million years after the big bang.
Webb will be able to observe certain hot, young exoplanets using a technique called direct imaging.
Equipped with sensitive spectrographs, Webb will be able to detect oxygen and other organic molecules in the atmospheres of nearby exoplanets. These organic molecules will reveal clues to the potential habitability of other worlds.