An astronomical object somewhere in the Planetary System, the Galaxy, a Cluster of Galaxies, or far out in the Universe may generate radio waves by one or the other physical process (a topic of Astrophysics). If the radio emission is generated inside the object, some of the radio waves propagate through the object until they may leave the radio source at its surface (Radiative Transfer). The emitted radio waves then propagate through the intergalactic, interstellar, and interplanetary space (Radiation Propagation) and finally through the Earth’s atmosphere (Atmospheric Physics). On the way through space and the Earth’s atmosphere, the radio waves are more or less severely absorbed and deflected from a straight path (Atmospheric Physics, Refraction). In addition, the orientation of polarization of the radio waves may be rotated (Faraday rotation) in a medium with free electric particles located anywhere along the path of propagation. Finally, the radio waves are collected by the radio telescope (Radio Optics), detected by the receiver (Radio Electronics), and analyzed and recorded in the spectrometer and computer (Data Acquisition).