If the sun is eight minutes away if you are travelling at the speed of light, since that's how long it would take for people to notice if the sun had stopped shining, how far can a short-wave radio signal travel in a vacuum at full power versus a long wave radio signal?

Think of radio communication on other planets, like humans possibly going to Mars.


closed as unclear what you're asking by Chris, The Photon, Jon Custer, Kyle Kanos, Michael Seifert Mar 7 '18 at 14:19

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    $\begingroup$ In vacuum, no difference. Note that light is really short wavelength radio waves... $\endgroup$ – Jon Custer Mar 6 '18 at 15:47
  • $\begingroup$ @JonCuster - The designation shortwave radio waves is reserved to the high frequency band 1.7–30 MHz (Wavelengths 176.3–10.0 m). Thus visible light with frequencies 430–750 terahertz (THz) or wavelengths 0.4 to 0.7 $\mu m$ is definitely not included in this. See en.wikipedia.org/wiki/Shortwave_radio $\endgroup$ – freecharly Mar 6 '18 at 16:13
  • $\begingroup$ What does the sun have to do with it? What does "at full power" mean? Are you asking "How far can a signal at full power travel?" Are you "How far can a signal travel while remaining at full power?" $\endgroup$ – Acccumulation Mar 6 '18 at 16:49
  • $\begingroup$ @freecharly, "shortwave" is a specific band. "Short wavelengths" just means wavelengths that are short. Light definitely has short wavelengths compared to radio. $\endgroup$ – The Photon Mar 6 '18 at 16:57
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    $\begingroup$ @freecharly - as an Amateur Extra licensed ham radio operator, I'm well aware of the (quite variable mind you!) frequency designators. The point was that light is light in vacuum, whether rf, visible, or gamma... $\endgroup$ – Jon Custer Mar 6 '18 at 18:40

If you are just asking about distance, there is no theoretical limit to how far a radio wave can travel. Regarding communicating between Earth and Mars, yup, we've already done that with several instruments, i.e. orbiters and rovers we've sent there.


The speed of all electromagnetic waves in vacuum is equal to the speed of light. Thus all radio waves, i.e., longwave, shortwave, ultra-short wave radio waves, microwave waves; light waves, i.e., infrared to visible and ultra-violet light; and x-ray and gamma-ray waves all propagate at the same speed of approximately 300000 km/s. Thus radio signals to the sun would take the same 8 minutes as visible light.


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