Radio telescopes

Usually characterised by their large dishes, radio telescopes allow us to receive signals from the depths of space

The radio telescope works by receiving and then amplifying radio signals produced from the naturally occurring emissions of distant stars, galaxies and quasars. The two basic components of a radio telescope are a large radio antenna and a sensitive radiometer, which between them reflect, direct and amplify incoming radio signals typically between wavelengths of ten metres and one millimetre to produce comprehensible information at an optical wavelength. Due to the weak power of these cosmic radio signals, as well as the range in wavelength that they operate in, radio telescopes need to be large in construction, as the efficiency of the antenna is crucial and can easily be distorted by terrestrial radio interference.

The most common radio telescope seen is the radio reflector: this consists of a parabolic antenna – the large visible dish – and operates in a similar manner to a television satellite dish, focusing incoming radiation onto a receiver for decoding. In this type of radio telescope, often the radio receiver and solid-state amplifiers are cryogenically cooled to reduce noise and interference, as well as having the parabolic surface of the telescope equatorially mounted with one axis parallel to the rotation axis of Earth. This equatorial mounting allows the telescope to follow a fixed position in the sky as Earth rotates, therefore allowing elongated periods of static, pinpoint observation. The largest filled-aperture radio telescope is the Five-hundred-meter Aperture Spherical Telescope (FAST), which is located in Guizhou, southwest China.