As discussions and answers to How large does refraction become in radioastronomy? point out, it is difficult to do radio astronomy much below 30 MHz (or 10 MHz depending on how aggressive you are in correcting for ionospheric effects like wavefront distortion and scintillation) from Earth's surface due to our ionosphere, which has made AM and short-wave radio listeners and ham radio operators happy for almost a century by being so reflective.

But that doesn't necessarily mean that there's no interesting radio astronomy way below 30 MHz.


  • What can be learned from low frequency radio astronomy available outside of Earth's ionosphere?
  • Are there currently any proposed or planned space-based low-frequency radio-telescope efforts?
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    $\begingroup$ You might want to look into the research done by Grote Reber, an American radio astronomer who moved to Tasmania in the 1954 to study radio signals in the 0.5 to 3 MHz range. $\endgroup$ – Fred Dec 20 '19 at 10:58
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    $\begingroup$ [History of Low Frequency Radio Astronomy in Australia 1](www.narit.or.th/en/files/2015JAHHvol18/2015JAHH...18..312G.pdf), [History of Low Frequency Radio Astronomy in Australia 2](www.narit.or.th/en/files/2015JAHHvol18/2015JAHH...18...14G.pdf) & History of Low Frequency Radio Astronomy in Australia 3. Podcast $\endgroup$ – Fred Dec 20 '19 at 11:19
  • $\begingroup$ @Fred I have quite an interest in early radio astronomy but don't know much about it, thanks! $\endgroup$ – uhoh Dec 20 '19 at 11:25
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    $\begingroup$ How low is "low"? The plasma frequency in the interplanetary medium near the Earth is about 100 kHz. physics.stackexchange.com/a/519164/43351 $\endgroup$ – Rob Jeffries Dec 20 '19 at 19:53
  • $\begingroup$ @RobJeffries that's good to know, thanks! In this case "low" was defined as below what can be observed from inside the ionosphere. $\endgroup$ – uhoh Dec 21 '19 at 3:14

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