J band

Within astronomy, the term J band refers to an atmospheric window within the near-infrared range roughly centered on 1.22 microns (1220 nm), which is about 240 THz. The term J band is also used for passbands of various photometric systems designed to use this window, e.g., with a full width at half maximum of 230 nm. In addition to infrared-specific telescopes, many optical telescopes can observe in this range. The letter is also used to indicate the magnitude of the signal observed through the passband filter, e.g., citing "J = 1.5". The passband is incorporated into the 2MASS JHK photometric system, as well as other infrared photometric systems. Note that there is some variation in such bands, regarding the central wavelength and the FWHM, between different systems and surveys, but versions of the J band are generally designed to observe through the J atmospheric window.

The term J band also has other meanings outside astronomy, one being a radio communications band, which is nowhere near the above infrared band.