Each letter designates a section of light of the
electromagnetic spectrum; these cover well the consecutive major groups, near-
ultraviolet (NUV),
visible light (centered on the V band), near-
infrared (NIR) and part of mid-infrared (MIR). The letters are not standards, but are recognized by common agreement among
astronomers and
astrophysicists. The use of U,B,V,R,I bands dates from the 1950s, being single-letter abbreviations. With the advent of infrared detectors in the next decade, the J to N bands were labelled following on from near-infrared's closest-to-red band, I. Later the H band was inserted, then Z in the 1990s and finally Y, without changing earlier definitions. Hence, H is out of alphabetical order from its neighbours, while Z,Y are reversed from the alphabetical – higher-wavelength – sub-series which dominates current photometric bands. Note: colors are only approximate and based on wavelength to sRGB representation (when possible). Combinations of these letters are frequently used; for example the combination JHK has been used more or less as a synonym of "near-infrared", and appears in the title of many
papers. == Filters used ==