MadSci Network: Astronomy

Re: Where can I find out how to make an inferometer?

Date: Fri Dec 15 14:02:57 2000
Posted By: Erika Gibb, Grad student, Physics & Astronomy/Origins of Life, RPI
Area of science: Astronomy
ID: 976510849.As

Hi Mitchell!

The technique of interferometry is where the light waves from two or more
telescopes are combined.  This increases the resolution (basically a
measure of how close two objects can be in the sky and still be seen
separately instead of blended together) to the equivalence of a single dish
with a diameter equal to the separation between the telescopes.  The light
gathered by the telescopes is not proportionally increased (that depends on
the size of a dish but not on the combination of light from separate
telescopes), so this technique is often used to make precision measurements
of stellar positions, for example, and not for looking at deep sky objects.

Building an interferometer, as you have surmised, will not be easy.  You
need to decide what wavelength you wish to observe in.  Because of the
shorter wavelengths involved (by 5 orders of magnitude usually), optical
interferometers are much more difficult to build than radio
interferometers.  You need to know precisely how far apart your telescopes
are.  They need to be protected from vibrations (such as wind).  Combining
the waves from two or more radio dishes to give a correct fringe pattern
will require knowledge about receivers, amplifiers, and computer programs
for data analysis that I cannot say much about.  I will refer you to a
couple books that may prove useful in helping you determine how to build
your own interferometer.

"An Introduction to Radio Astronomy" by Bernard F. Burke and Francis
Graham-Smith gives some general information about the concepts behind
aperture synthesis and some of the imperfections that will need to be
accounted for in a real array.  "Radio Astronomy" by J.D. Kraus is another
good book, slightly more technical than the one by Burke, it covers
technical information about many individual telescopes and receivers as
well as going into detail about concepts behind radio astronomy.  One very
technical book that may be of help in building an interferometer is
"Optical Shop Testing" by Daniel Malacara (Editor).  However, I understand
that this is a very mathematically rigorous book.  It does have information
on testing techniques and may be helpful if you are serious about
constructing your own interferometer.  Hopefully these sources will help
you get started.

For others who want more information on interferometers, a quick and easy
project demonstrating the fringes resulting from an interferometer can be
found at the nasa web site:


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