In radio astronomy, the flux unit or jansky (abbreviation Jy) is a non-SI unit of electromagnetic flux equivalent to <math>10^{-26}<math> watts per square metre per hertz. The name "Jansky" is named after the pioneering radio astronomer Karl Jansky.
The brightest natural radio sources have flux densities of the order of one jansky, which makes the jansky a suitable unit for radio astronomy.
