The Jansky (Jy) is a CGS (non-SI) unit of spectral Flux density equivalent to 10-26 Watts per square meter per Hertz. It is often used in Radio astronomy to describe the brightness of sources at particular Frequencies. Examples:
Some common variants are Millijansky (mJy, also referred to as m.f.u. for Milli Flux Unit), and Megajansky (MJy).
1 Jansky Empty Field Survey (1 Jy)