gigajanskys

Gigajansky (GJy) is a non-SI unit of spectral flux density used in radio astronomy. It represents 10^9 janskys, and since one Jansky equals 10^-26 W m^-2 Hz^-1, one gigajansky equals 10^-17 W m^-2 Hz^-1.

The jansky, named after Karl Jansky, is the conventional unit for expressing the flux density of astronomical radio sources. The gigajansky, by contrast, is rarely used and generally serves to illustrate extremely bright signals or upper bounds in discussions of dynamic range. Actual observed sources typically lie far below 1 GJy, and measurements are commonly reported in jy or mJy.

In practice, the gigajansky is not standard in data products and is mostly encountered in theoretical discussions or as a way to express extreme possibilities rather than routine observations. When used, it is important to keep the distinction between Jy-based measurements and SI-derived units clear, and to remember that 1 GJy equals 10^-17 W m^-2 Hz^-1.

See also: Jansky; flux density; radio astronomy; spectral flux density.