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I know the EM spectrum goes off both ends, but nearly everything anyone has bothered to use it for has wavelengths between $10^8$m (ELF) and $10^{-12}$m or so (gamma rays). So for the purposes of this question lets just assume those 20 orders of magnitude represent everything of interest.

So then the question: how much hardware would it take to be able to observe all of that? Say if you are building a space probe? Would it be reasonable to assume that the average sensor could handle an order of magnitude window in that spectrum? More then that? Less than that?

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  • $\begingroup$ A space probe to detect $10^8$ meter radiation? I don't think that's remotely possible. $\endgroup$ Aug 15 at 19:43
  • $\begingroup$ @DavidHammen: IIRC an antenna can be significantly smaller than a wavelength, (AM radios use between $10^2$ and $10^3$ shorter.) Assuming 30 Gage aluminum wire, that's just short of 40 tons, or about twice what a Falcon Heavy can send to mars. Expensive and by no means simple, but within the possible. -- OTOH: would those same wires work for $10^5$m? $10^4$m? $\endgroup$
    – BCS
    Aug 15 at 22:07
  • $\begingroup$ @DavidHammen Submarines can receive messages sent to them in the ELF range (due to it's strong ability to penetrate water). I can't imagine most submarines are $10^8\ m$ in size. $\endgroup$
    – zephyr
    Aug 17 at 21:21
  • $\begingroup$ @zephyr Different organizations have different definitions of what ELF means. To the US Navy, 76 Hz qualified as extremely low frequency, which was what was used in Project ELF. That's a wavelength of about 4000 km. A receiving antenna doesn't have to be as long as the wavelength. An antenna several kilometers long will do. Russia uses 82 Hz, so an even shorter wavelength of 3700 km. $\endgroup$ Aug 18 at 1:54
  • $\begingroup$ @BCS Besides the sheer impossibility of detecting 3 Hz ($10^8$ meter) radiation, why? The low frequency region that is attainable by spacecraft and offers useful science is the 100 kHz to 20 MHz range. This frequency range is unavailable to Earth-bound observatories because of the ionosphere, but could give us insights into the early universe (the interval between the CMBR and the first galaxies). $\endgroup$ Aug 18 at 2:07

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