Radio astronomy

Radio astronomy is astronomy which studies celestial objects at radio frequencies. 
The first detection of radio waves from an astronomical object was made in the 1930s. Karl Jansky found radiation coming from the Milky Way. Later, other sources of radio emission were found. These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. 
The discovery of the cosmic microwave background radiation, evidence for the Big Bang theory, was made through radio astronomy.
Radio astronomy is done using large radio antennas. These are called radio telescopes. They are used alone, or with multiple linked telescopes. The use of interferometry allows radio astronomy to achieve high angular resolution. The resolving power of an interferometer is set by the distance between its components, not the size of its components.