This is Saturn, as seen by the Very Large Array (VLA) radio telescope. The bright disk of the planet gradually fades toward the edge, an effect called limb darkening. It’s caused by the gradual cooling moving outward in Saturn’s atmosphere. The rings are seen as emitters of energy outside the planet’s disk, but in front of the planet they absorb the radiation from the bright disk behind and appear as a dark band. That’s in contrast to their appearance in visible light where they reflect the incident sunlight. At radio wavelengths sunlight is much fainter, and we see the actual radio emissions from Saturn.
Image Credit: NRAO