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Radio Astronomy: How It Differs From Optical Astronomy

BIMA Consortium
banner image of Galaxy 3627
Galaxy NGC 3627

Radioastronomy differs from optical astronomy on two main counts:

A Different Telescope Design

Very Large Array (VLA)
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Radiowaves possess much longer wavelengths than do lightwaves. Thousands to over millions of times longer. To match the precision (or rather the resolution) of their optical counterparts, radio telescopes need to span a much larger diameter. For example, a radiotelescope must extend 1000 feet across in order to reveal the same amount of detail as an optical telescope a mere one foot in diameter.

Constructing a 1000 feet telescope poses a formidable engineering challenge. This is a major reason why radioastronomers prefer to combine several smaller telescopes, more commonly referred to as receiving dishes, into an array.

Together, the dishes can act as one large telescope whose size equals the total area occupied by the array. So an array equivalent to a one thousand feet diameter telescope could be assembled by spacing a number of much smaller dishes across that same distance.

Different Information

Milky Way Galaxy in CO
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Radio waves, just like light waves, constitute part of the the electromagnetic spectrum but reveal different types of information. Visible light tends to indicate the physical properties of single atoms emitting or absorbing light energy. In contrast, the millimeter radio waves picked up by the BIMA array are better at providing information about the behavior of combinations of atoms, i.e. molecules. Yet distinct types of information are obtained by studying radio energy emitted at centimeter wavelengths. Another radiotelescope, the Very Large Array, is well-equipped for such observations.

Jack Welch, on-camera
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QuickTime Movie (2.3 MB); Sound File (1.3 MB); Text

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NCSA. Last modified 11/11/95