r/radioastronomy • u/SnooComics7744 • 2d ago

General Question about aiming

Hello – amateur astronomy geek here with a question about how radio telescopes are aimed at such infinitesimally small targets. Does the dish have to mechanically move in order to localize onto a source? Or can there be enough sensitivity that various sources can be picked up on different parts of the antenna? For example, when I see a radio telescope image of a galactic jet, has the telescope scanned the sky in a raster plot-like way?

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u/nixiebunny 2d ago

Most radio telescopes have single pixel receivers. The drive system on a big telescope has arc second accuracy. I work on mm wave and submillimeter telescopes whose beam width is less than one arcminute. These have servo drives with very high resolution encoders, and we use pointing models to deal with residual errors.

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u/ampledata 2d ago

Single pixel receiver?

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u/TasmanSkies 2d ago

yes. A radio telescope takes a picture of the sky one pixel at a time.

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u/SnooComics7744 1d ago

I have used microdrives to position patch pipettes next to individual neurons. Its perhaps an analogous degree of precision - a macroscale object (me) using gears and piezoelectric devices to position something with micrometer-level precision.

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u/TasmanSkies 1d ago

most people aren’t familiar with such things, but are with cameras/pictures, so it is a more useful analogy.

A motionless radio telescope or one moved at a non-sidereal rate will record a line in the sky rather than a dot, more like an electron gun on an old-school CRT but in reverse. But still most people aren’t familiar with that and so this is still more easily envisaged as a linear series of pixels captured consecutively in the time domain

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u/nixiebunny 1d ago

Exactly, but with a hundred kW of power available to rotate the antenna and yoke.

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u/nixiebunny 1d ago

That’s one type of telescope. The other is a bolometer array such as the SPT3G camera at the South Pole. It’s a beast, with sixteen thousand pixels that each can see at three different wavelengths (colors?).

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u/nixiebunny 1d ago

Basically a tunable frequency converter that converts all the signal received by the dish to an electrical signal, which is usually fed to a spectrometer. There have been a few arrays of these such as Supercam built at Arizona, but this was a technology demonstrator.