As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image.

A single antenna radio telescope's signal is focused on some sort a sensor but this signal represents only a single 'pixel.' To generate a composite image of an object, a time intensive scan pattern needs to be carried out.

Why does this difference exist? Why does a radio telescope see a single pixel, while optical telescopes see an entire image? Are radio telescope sensors only a single pixel, or is a radio telescope itself, regardless of the sensor, only capable of seeing a single pixel?


It's all because of the wavelength of light.

In most bands the radio telescope is about the size of the wavelength it's observing - so it can only see a single point at once anyway. It would be like having an optical telescope that was a tiny microscopic pinhole - there wouldn't be much point in having a megapixel camera behind it. Radio telescopes that work with mm wavelength band now have multi-pixel detectors.

To get comparable resolution to an optical telescope with wavelengths that are a million times longer we would need a telescope a million times larger. So we link radio telescopes together - to make a single telescope. Each telescope measures a single part of the incoming signal and we re-create the detailed picture later in a computer.

  • $\begingroup$ That makes perfect sense, I thought it might be related to the wavelength of the signal. Thank you very much for the answer! $\endgroup$
    – monolith
    Nov 29 '13 at 17:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.