1. A unit of radiation received from outer space, used in radio astronomy: A jansky is equal to 10^-26 watts per square meter per hertz, and is named for the U.S. radio engineer, Karl Jansky (1905-1950).

A jansky unit used to indicate the strength of radio sources in astronomy.
2. A unit of work or energy in the International System of Units (SI): A jansky is equal to the work done by a force of one newton (that force necessary to provide a mass of one kilogram with an acceleration of one meter per second per second).