An Etymological Dictionary of Astronomy and Astrophysics

1. Three → atmospheric windows in the → near infrared portion of the → electromagnetic spectrum at 1.25 (J), 1.65 (H), and 2.20 (K) μm.
   

2. An extension of Johnson’s → photometric system into near infrared using filters corresponding to the atmospheric windows J (1.25 μm), H (1.65 μm), and K (2.20 μm), with → bandwidths 0.3 μm, 0.4 μm, and 0.6 μm respectively.

See also: Letters of alphabet, used conventionally; → system.