Australia Telescope National Facility

Introduction to Radio Astronomy and Interferometry

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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.

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

If a source being observed covers an angle in the sky much smaller than the ratio (detected wavelength)/(twice the separation between two radio telescope dishes) then the combined output from the pair of dishes observing the source oscillates strongly with time. The ratio above is called the resolution of the telescope. As the separation between the dishes increases, the angular size of source that the telescope can detect decreases. For sources of angular size much larger than the resolution, the output ceases to vary and less information can be obtained about the sources. To study large-scale structure, astronomers need to use a lower resolution ie a more closely spaced pair of dishes. An interferometer works most efficiently, in the sense of returning the most information about the intensity and size of the source being observed, for a source whose size is comparable with the telescope's resolution.

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.

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Last update by Michelle Storey. 14/2/99

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