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jansky(jan -skee) Symbol: Jy. The unit of flux density adopted by the IAU in 1973 and used throughout the spectral range, especially for radio and far-infrared measurements; it is named after Karl Jansky, who discovered radio emission from the Milky Way in 1932. One jansky is equal to 10–26 watts per square meter per hertz. It is possible to calculate the equivalent flux density, S ν, in janskys from a value of magnitude at the effective wavelength, λeff, appropriate to a particular optical or infrared filter (see table). For example, an R magnitude of 3.2 corresponds to a flux density at 0.7 μm of
a subsidiary unit of the spectral density of radiant flux. Used in radio astronomy, it is named in honor of K. Jansky (1905–50), an American scientist who discovered cosmic radio emission in 1932. Its abbreviation is Jy; 1 Jy = 10–26 watt per square meter per hertz.