Last week, I looked at the electromagnetic spectrum. At the one end of this continuous band of electromagnetic radiation, we have radio waves.
Radio waves cannot be seen with the human eye. They carry the least amount of energy and have the longest wavelengths of all the electromagnetic wave categories. They're also incredibly useful in the field of astronomy.
What is radio astronomy?
Simply put, radio astronomy studies objects in the sky that give off radio waves. In our Solar System, the Sun and Jupiter give off radio waves. And, further away, the centre of our galaxy (the Milky Way), giant explosions called supernovae, and exotic celestial objects call pulsars and quasars are all radio sources.
Radio astronomy allows us to probe regions of space that cannot be seen using visible light. This is because radio waves can pass through dust, so radio astronomy has unmasked previously invisible regions of space.
It also means that, unlike optical telescopes, radio telescopes are not hampered by clouds or poor weather.
How does a radio telescope work?
Radio telescopes are massive structures because they have to capture the long wavelengths of the radio spectrum. The largest radio telescope in the world as a single dish, is the Arecibo telescope. It was featured in the movie Contact, and is located in a natural hollow in Puerto Rico, South America. You may also be familiar with the Lovell radio telescope at Jodrell Bank (which is also one of the favourite places on planet Earth - I'd highly recommend a visit).
This huge white bowl of Lovell (and other radio telescopes) reflects incoming radio waves into the focus box mounted on top of the central tower. Here, at the focal point of the reflector, a small aerial picks up the waves and feeds them into a sensitive radio receiver where the signal can be transported and analysed.
To make a clearer (or higher resolution) radio image, radio astronomers often combine several radio telescopes into a pattern called an array. Together, these dishes act as one large telescope whose size equals the total area occupied by the array. This is a technique called interferometry.
The Very Large Array (VLA) in New Mexico consists of 27 radio telescopes, arranged in a Y-shaped configuration. Each telescope is 25 metres in diameter. All 27 telescopes are used simultaneously to observe a target, then their observations are added together.
Extra reading and watching
To get an in-depth view of radio astronomy, the National Radio Astronomy Observatory is a great place to start and Jodrell Bank's website is a mine of useful information. Also, check out this page if you want to find out more about radio interferometry.
It's not just the radio spectrum that you can use to probe the universe. You can also use gamma rays, X-rays, ultraviolet radiation, infra-red and microwaves.
This is a wonderful talk from radio astronomer Natasha Hurley-Walker too:
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