Auroral kilometric radiation (AKR) is the intense radio radiation emitted in the acceleration zone (at a height of three times the radius of the Earth) of the polar lights.
The radiation is absorbed by the ionosphere and therefore can only be measured by satellites positioned at vast heights, such as the Fast Auroral Snapshot Explorer (FAST).
According to the data of the Cluster mission, it is beamed out in the cosmos in a narrow plane tangent to the magnetic field at the source.
The sound produced by playing AKR over an audio device has been described as "whistles", "chirps", and even "screams"[citation needed].
As some other planets emit cyclotron radiation too, AKR could be used to learn more about Jupiter, Saturn, Uranus and Neptune, and to detect extrasolar planets.