If I search online for how radio telescopes work, the found articles talk about how RF is on the spectrum, etc, how the parabolic collector is the aperture which contributes to the sensitivity and reflects the signals into the detector at the focal point. Then they skip to the signal processing circuitry the leads to a rendered image. They also mention that the furthest nodes in a telescope array determine the virtual aperture of the array.
There are a few parts I don't understand: How does the detector work? From my reading, it is merely an RF antenna. I can't think how you'd get but one pixel per "moment" of detection. That the telescope is positioned and begins listening, and as the earth turns one scan-line of image is captured. For high resolution 2D image this would take thousands of passes. This seems impractical as the earth is orbiting and time marches on, otherwise.
Perhaps multiple telescopes each take a scan line and interlace the results … but especially at such high resolutions, I can't see how you'd engineer the huge machines with such precision. Please explain this to me.
Do I have the 1D scan-line-antenna idea wrong? Is it more like a 2D CCD sensor in a digital camera with the antenna just behind the focus of the dish? If so, I assume the sensor would have to be a 2D array of nanometer scale antennas?
This may be clear in the explanation, but in layman's terns, how are do telescope arrays work together to create the virtual aperture? What is lost, if any between the virtual and a theoretical "real" aperture of equal size?
(I consider this a physics question because understanding the answer to this real-world application will help correct whatever theoretical misconceptions I have about RF, antennas, and radio telescopes)
Thanks!
Best Answer
In the microwave band here are multi-element detectors, but at longer wavelengths the telescope is a single pixel.
Yes it does take a while to build up an image, but radio pictures aren't usually very large - not the millions of pixels of an optical/IR image.
One big advantage of radio telescopes is that you can combine telescopes 1000s of km apart to create an image with the resolution of a single dish that large ( you can just about do this in the optical with 100m separation now)
You know about the interference pattern you get with two slit? If you picture the two telescopes as the two slits and you interfere (electrically) the signals to form the fringe pattern. You can then calculate the shape of the light source - a single point will produce the classic fringe pattern, 2 close points will produce a slightly different pattern etc.
edit: Building an optical 'radio' telescope - the original English solution and the rather more impressive Teutonic result (if you have a lot more $$$)