The Fanaroff-Riley classification is a scheme created by B.L. Fanaroff and J.M. Riley in 1974, which is used to distinguish radio galaxies with active nuclei based on their radio luminosity or brightness of their radio emissions in relation to their hosting environment. Class I (abbreviated FR-I) are sources whose luminosity decreases as the distance from the central galaxy or quasar host increase, while Class II (FR-II) sources exhibit increasing luminosity in the lobes. These sources are called also edge-darkened. This distinction is important because it presents a direct link between the galaxy's luminosity and the way in which energy is transported from the central region and converted to radio emission in the outer parts.
- Fanaroff, Bernard L., Riley Julia M.; Riley (May 1974). "The morphology of extragalactic radio sources of high and low luminosity". Monthly Notices of the Royal Astronomical Society 167: 31P–36P. Bibcode:1974MNRAS.167P..31F.
- Tsinganos, Kanaris C.; T. Thomas P., Ray; Stute, Martin (2009). Protostellar Jets in Context. Astrophysics and Space Science Proceedings. Springer. p. 276. ISBN 9783642005763. Retrieved 2013-01-11.
- "Fanaroff-Riley Classification". NASA/IPAC Extragalactic Database (NED). Caltech. Retrieved 11 January 2013.