Australia Telescope National Facility

Introduction to Radio Astronomy and Interferometry

Paragraph 3

For more information on each of the sentences below, click on the text of the sentence. For more information on all the sentences click here.

Radio astronomy uses radio waves to study regions of space.

Single-dish radio telescopes produce blurry images.

Interferometry is a technique used to overcome the blurring and produce sharper radio images.

Astronomers are able to electronically simulate the effect of a very large dish by using the combined signal from many smaller single-dish radio telescopes. The technique they use is called interferometry. Interferometry exploits one advantage of the much larger wavelength of radio waves, which is that detectors can be used which measure the phase as well as the intensity of the radio waves received. If a pair of single-dish radio telescopes, separated on the ground, observes a single small source, the combined output oscillates with time. This is because, as the Earth rotates, the relative phase of the signals received by the two dishes varies as the distances from the source to each dish vary. This means that sometimes the radio wave from the object received by the two different dishes will add up in phase and produce a large signal and sometimes be out of phase and produced a small signal, depending on the slightly different distances from the object to each dish. Interferometry uses the constructive and destructive addition of the radiation to determine information about the intensity and size of the object being observed.

The spacing between the radio telescope dishes in an interferometer determines the size of the objects that can be resolved by the interferometer.

Using many dishes together in an interferometer array allows astronomers to form more complete images of objects.

This is how an aperture synthesis telescope such as the Australia Telescope Compact Array works.

VLBI (Very Long Baseline Interferometry) enables very small objects to be clearly resolved.

---

Go to Introduction to Radio Astronomy and Interferometry Summary

Last update by Michelle Storey. 14/2/99

---