Final answer:
Radio telescopes sensitive to microwaves primarily detect Cosmic Microwave Background Radiation from the Big Bang. They can also observe galactic and solar radiation but are distinct from instruments designed to detect infrared radiation.
Step-by-step explanation:
Radio telescopes sensitive to microwaves are used to detect several types of astronomical phenomena, including the Cosmic Microwave Background Radiation (CMB), which is the cooled remnants of the radiation from the Big Bang. In 1964, Arno Penzias and Robert Wilson discovered this microwave radiation and helped establish the widely accepted theory of the universe's origin. Beyond the CMB, these telescopes can also detect galactic and solar radiation, but they are not typically used to detect infrared radiation because the microwave and infrared regions of the electromagnetic spectrum overlap and require different detection methods. The radio telescopes such as the Arecibo Radio Telescope in Puerto Rico and Parkes Observatory in Australia, are famed for their role in such discoveries.