I have a question about Radio Astronomy. I have recently visited the VLA, and one thing I don't understand, is how they turn the signals into a picture. A regular optical telescope is obvious, the image is focused onto a plane. It's already an image. But the dishes at the VLA, the way I see it, are collecting individual point sources of data. How is that assembled into a 2D image? Is there documentary or video that explains the math involved? I asked this question and the tour guide and she referred to the grad students. They started into this explanation about FFT, but I don't see how separating out individual frequencies gets you to a 2D picture. (Other than a graph of frequency distribution.) &Astronomy
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4 comments
Feel free to reply to any comment by clicking the "Reply" button.Are you thinking of the dishes as looking at one point source each? That's where you would be going wrong. It might work better if you thought of them as many single point source detectors that get added together to create the image.
Stephanie99
Level 8
July 8, 2018
0
It takes all of the 27 dishes to see a single point source. That's because the wavelength of the signal is so large.
@novoxguy Would this help you? [space.com]
@novoxguy The sky is big. Are you sure about that?
@Stephanie99 Hubble is an optical telescope. The VLA is a Radio Telescope. A different animal. See the pic of me standing in front of a couple of the dishes.
Do you guys know what a light sensor is? The device that automatically turns lights on, when it get's dark? That collects light as a point source. A camera also picks up light, but as an image. The radio telescopes picks up like the light sensor, an optical telescope is like a camera. What I want to learn, is how they can take 27 dishes and produce a picture. Which they do.
novoxguy
Level 6
July 8, 2018
0
@TheAstroChuck I was speaking to the early posters that didn't have a clue. Thanks for your input.
wouldn't the pattern in the wave or "region" of waves be similar to that of light? brightness=amplitude, wavelength=color, frequency=value etc.....idk. good question.
hankster
Level 9
July 7, 2018
0
Yes, but with the VLA they can produce a picture of solar systems and galaxies. An image where a dot in the picture, represents a radio source, instead of a light source.
@novoxguy please understand I know absolutely nothing about this stuff. it just seems to me in the case of the Galaxy, it's just a radio Source location instead of a light source location, and so that we can see it with our own eyes its plotted as a white dot on a dark background. perhaps I'm out of my depth here..
Fast Fourier Transformation FFT is a mathematical principle. Let's leave it at that. The algorithm analyzing the data, has the capability to translate the information based on frequencies into densities that can be presented in two dimensional charts that can be interpreted with our senses limitation. Sorry man, I thought I was going to come up with a better intuitive explanation. Your question is challenging, to say the least. Hope this helps.
IamNobody
Level 8
July 7, 2018
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