sci.astro
[Top] [All Lists]

Re: Interferometry of a Monotonic Source?

Subject: Re: Interferometry of a Monotonic Source?
From: Martin Brown <|||newspam|||@nezumi.demon.co.uk>
Date: Wed, 08 Mar 2006 11:44:19 +0000
Newsgroups: sci.astro
W. Watson wrote:

Martin Brown wrote:

W. Watson wrote:

The methodology for interferometry looks fairly hairy for most people who may not be acquainted with Fourier analysis.

There is a toy Java interferometer on the web where you can see the visibility fringes from various common sources.

http://www.narrabri.atnf.csiro.au/astronomy/vri.html

I guess another thing that disturbs me about many explanations is how two observers can be as effective resolution-wise as an instrument whose diameter is the same as the distance between them, albiet seeing the object as a dimmer. Intuitively it doesn't seem to make sense;

That is because it doesn't. You need a suitable set of observations in visibility space to compute an aperture synthesis image. Measuring a single spatial frequency on its own is not enough to form an image.

To compute an image you need a combination of obervations of the visibility fringes made across a whole set of baselines to fill in the equivalent aperture. The earliest version of Earth rotation aperture synthesis used a perfect E-W baseline (Cambridge One Mile) to use the Earths rotation to collect a pair of baselines with one movable scope. The 5km scope relaxed the E-W requirement a bit, and the VLA using superior computer power broke free and is able to handle a Y shaped set of baselines allowing snapshots as well as deeo synthesis.

 however,
it seems demonstratable by masking a simple telescope's mirror. In the simplest case, this seems possible to demonstrate by putting one's hand in front of the tube of a Newtonian, and looking through the eyepiece. I would think a better demonstration would be to mask the mirror instead by covering some inner ring of the mirror.

To see what aperture synthesis fringe measurements look like in the optical you need a pair of smallish holes in a cardboard mask and the ability to rotate it. Point the whole lot at a near equal brightness double star and with any luck you will see the interference fringes vary in intensity as you rotate the mask relative to the sky.

<Prev in Thread] Current Thread [Next in Thread>