How do radio maps of the sky differ from ordinary star maps?

Ordinary star maps and radio maps differ primarily in the type of radiation they detect and the instruments used to create them.

While modern astronomical maps are typically compiled from photographic observations of stars and galaxies using Earth-based or space-borne optical equipment, radio maps are generated using radio telescopes. These instruments utilize antenna systems and receivers to detect radio-frequency radiation—ranging from 1 mm to 10 metres in wavelength—emitted by celestial sources such as stars, galaxies, and quasars.12

Radio maps reveal cosmic phenomena that are not necessarily visible to the human eye or standard optical telescopes. For instance, early radio mapping identified "noise" originating from the center of the Milky Way Galaxy. Furthermore, specialized missions like the Wilkinson Microwave Anisotropy Probe have used microwave receivers to map the cosmic microwave background, providing insights into the early universe's density variations and composition that optical star maps cannot provide.13