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.
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.
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.