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Re: Interferometry of a Monotonic Source?

Subject: Re: Interferometry of a Monotonic Source?
From: "William C. Keel"
Date: 13 Mar 2006 07:55:24 -0600
Newsgroups: sci.astro
W. Watson <wolf_tracks@xxxxxxxxxxx> wrote:
> The descriptions I've seen of the u-v coverage are pretty sketchy, to me at 
> least. Apparently, it is fomred by looking at a baseline pair as seen from 
> the source's view in space as the earth rotates. Somehow this view should 
> when plotted against time look like an ellipse. If I simply take two points 
> on a globe and connect them, and look at them as I rotate the globe, then I 
> don' see what might be taken as an ellipse. One description I saw talks 
> about projecting the earth points onto a plane perpendicular to the line of 
> sight.  Maybe some warpage in the projection does cause part of an ellipse 
> to appear on that plane.

> Isn't the u-v plane a frequency domain? How does this related to x-y (and 
> maybe z) on the earth?

A single-baseline interferometer at a given time samples a
point in the (u,v)-plane which is the vector of baseline components
perpendicular to the line of sight of the source, most conveniently
measured in units of the wavelength being used. The ellipses
for most source declinations come because, _when seen from the
source direction_, the Earth's rotation makes the baseline sweep out
a section of an ellipse (becoming degenerate to a circle at a
celestial pole and an E-W line at the equator). 

Bill Keel

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