JWST carries four primary science instruments: NIRCam, NIRSpec, MIRI, and NIRISS. Together, they give Webb imaging, spectroscopy, coronagraphy, and other observing capabilities across visible red and infrared wavelengths.
NIRCam, the Near Infrared Camera, is Webb’s main imaging instrument and also helps align its segmented mirror. NIRSpec, the Near Infrared Spectrograph, can record spectra from many objects at once. MIRI, the Mid-Infrared Instrument, observes longer infrared wavelengths and includes both imaging and spectroscopy. NIRISS, the Near Infrared Imager and Slitless Spectrograph, supports specialized spectroscopy and high-contrast observations.
Webb also carries the Fine Guidance Sensor, or FGS, which helps point the observatory precisely. The FGS is essential to operations but is not counted among the four primary science instruments. This distinction explains why some descriptions mention five instrument-related units while the standard science-instrument count remains four. The instruments are housed together in Webb’s Integrated Science Instrument Module, behind the telescope’s large primary mirror.