In radio astronomy, the flux unit or jansky (symbol Jy) is a non-SI unit of electromagnetic flux equivalent to 10⁻²⁶ watts per square metre per hertz. The unit "jansky" is named after the pioneering radio astronomer Karl Jansky. Microwave image of 3C353 galaxy at 8. ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... Electromagnetic radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ... In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks. ... The watt (symbol: W) is the SI derived unit of power. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The hertz (symbol: Hz) is the SI unit of frequency. ... Karl Guthe Jansky (October 22, 1905 – February 14, 1950), was the American physicist and radio engineer who in 1932 discovered that the Milky Way galaxy emanates radio waves; he did not follow up his discovery, but it marked the birth of radio astronomy. ...

The brightest natural radio sources have flux densities of the order of one (to one hundred) jansky, which makes the jansky a suitable unit for radio astronomy. Microwave image of 3C353 galaxy at 8. ...

For example the Third Cambridge Catalogue (3C) which was prepared in 1959 and revised in 1962, lists some 300 to 400 radio sources in the Northern Hemisphere brighter than 9 Jy at 159 MHz. 3C may refer to the digital radio station of the same name The Third Cambridge Catalog of Radio Sources (3C) is an astronomical catalogue of celestial radio sources as measured at 159-MHz. ...

1 Jy = 10^-26 W m^-2 Hz^-1 (SI) The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...

1 Jy = 10^-23 erg s^-1 cm^-2 Hz^-1 (cgs) The centimetre-gram-second system (CGS) is a system of physical units. ...

The flux in Jy can be converted to a Magnitude basis, for suitable assumptions about the spectrum. For instance, converting an AB magnitude to a flux in microjansky is straightforward:

F_v [µJy] = 10²⁹ 10^{-(AB+48.6)/2.5}