Any experts on Radio Astronomy - a Question

[Sparrow]

I was half watching a documentary a few months ago and wished I'd been able to give it my full attention - it was about radio astronomy - sorry but I can't remember what programme it was now.

Anyway, I know that radio astronomy detects radio emmissions and of course, thewavelenghts that Radio telescopes pick up is just another part of the elctromagnetic spectrum - it's all to easy to forget with visual astronomy that we only see a very narrow part of the elctromagnetic spectrum. I half picked up on something that they were saying in the documentary about radio telescopes being able to see further in to the universe (and of course therefore back in time) than those in the visible and infrared spectrum - the reason being that the shortwave visible light emmitted from distant galaxies continually "stretches" as it travels over the vast distances and therefore leaves the visible spectrum and eventually enters the radio spectrum. This was more than just the doppler red shift effect - I suppose it's the red shift taken to extremes.

Any experts who understand this and could perhaps explain to me a bit better.

[Sparrow]

Sorry - stupid me - didn't realise there was a forum specifically for discussing Radio Astronomy - perhaps one of the moderators could kindly move this to the correct forum.

Regards

John

[Ben Ritchie]

The cosmic microwave background is the light from the 'last scattering surface' (to use the technical term!) - it started as Black-Body radiation with a temperature of around 3000K, similar to a red giant star, so peaking in the red and near-infra red. Since then it's redshifted by a factor of about 1100 due to the expansion of the universe, so it's now detectable at radio wavelengths.

The most distant galaxies detectable today are at redshifts of under ten, so you get effects like the Hydrogen Lyman-alpha line, normally in the ultraviolet, shifting all the way to the near infra-red, but the redshifts aren't enough to move optical features to radio wavelengths - the advantage there of radio is that you can do very long baseline interferometry to give you very high angular resolution

[Talitha]

No problem John, i'll move it.

[Sparrow]

Thanks for that Ben - I sometimes think I ought to get more interested/involved in Radio Astronomy - I can't help feeling that I'm missing out on a lot. Especially living so near to Jodrell Bank (A visit there was my inspiration to get in to this hobby 35 years ago).

Regards

John