• Question: so what are radio telescopes?

    Asked by louistaylor1 to Jen on 18 Jun 2011.
    • Photo: Jen Gupta

      Jen Gupta answered on 18 Jun 2011:

      OK I’d better start at the beginning and explain what radio waves are. What we see as light is only a small part of what we call the electromagnetic spectrum. The electromagnetic spectrum goes from radio waves up to gamma-rays. It’s probably better to look this up on the internet so I don’t get sidetracked! There are lots of website that explain the electromagnetic spectrum, like this one on the NASA website: http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

      Radio telescopes are designed to detect the radio waves that are emitted by objects in space. They are normally huge dishes like the Lovell telescope at the Jodrell Bank Observatory (http://www.jb.man.ac.uk/aboutus/lovell/). The radio waves are reflected off the surface of the dish up to the receiver at the top of the tower in the middle.

      With radio telescopes, its a case of the bigger the better. However you can only make a telescope so big before it becomes too expensive and difficult to build. The largest radio telescopes that we can move around are the Green Bank telescope in the US (http://www.gb.nrao.edu/gbt/) and the Effelsberg telescope in Germany (http://www.mpifr.de/english/radiotelescope/index.html) – the Lovell telescope comes in third. The largest radio telescope dish is the Arecibo telescope (http://www.naic.edu/genpublic.php). So what we do instead is build lots of smaller radio telescopes and use them all to look at the same object in the sky. We can then combine the information using computers and it’s like having a massive telescope that’s as big as the area covered by the small telescopes! This is called interferometry. Interferometers include the Very Large Array (http://www.vla.nrao.edu/) and e-MERLIN (http://en.wikipedia.org/wiki/MERLIN) which is operated by my university. Lots of new interferometers are currently building built such as ALMA (http://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array) which is in the desert in Chile and is nearly finished.

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