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I What would it take to hear the Sun's sound from Earth?

  1. Jan 18, 2017 #1
    Sound pressure waves attenuate pretty quickly. On Earth we can not hear much of what is going on a few kms away, or above, or underground, unless it's some really catastrophic event of huge energy.

    But the Sun's energy output is hugely immense compared to even the most catastrophic event on Earth.

    My question is, if the Solar System interplanetary space between the Sun and Earth was full of (say) gas, could we hear the Sun's noise from Earth? what kind of gas density or other properties would be required? and what kind of sound would we hear? what frequencies, what level, a more or less constant roar or some big sound explosions?
    Thanks!
     
  2. jcsd
  3. Jan 18, 2017 #2

    phinds

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    If the Earth's atmosphere extended out to the sun, we would be squashed by the pressure most likely, so wouldn't be listening.

    BUT ... you counter ... this is just a thought experiment.

    Well, yeah, but thought experiments need to make sense.
     
  4. Jan 19, 2017 #3
    Thought experiments focus on what is wanted to be understood, not the practicality or feasiblity of the scenario. In this thread, I understood the OP really to be concerned with the pressure waves emanating from the sun, as sound, not the extension of atmosphere.*

    The range of frequencies audible would be dependant on (at least limited by) the thermal state of the medium, surely?

    The different regions of the sun have different interactions occurring at different pressures and densities. Therefore the resultant overall sound would be cacophonic white noise of so many overlayed frequencies.
     
  5. Jan 19, 2017 #4
    Apparently it's extremely soothing
     
  6. Jan 19, 2017 #5

    Chronos

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    The sun is a powerful emitter of radio waves. You can hear those with a properly tuned radio.
     
  7. Jan 19, 2017 #6
  8. Jan 20, 2017 #7
    Well radio waves have little to do with real sound pressure waves, that's a completely different meaning for "listening". Thank you all.
     
  9. Jan 24, 2017 #8
    Just to entertain the question "what kind of sound?", and not the part about what would the solar gas be like, which has problems in concept ... I would think sounds similar to the ocean, with masses moving and colliding would be the expectation. Perhaps large volcanic explosions, as suns spots erupted.

    Sounds are pressure waves in the auditory range and I share the dislike of calling something electronically translated thru a speaker a "sound". One can translate the digits of pi into a sound, but you are not "listening" to pi. You are listening to something else.
     
  10. Jan 24, 2017 #9
    Sound waves propagate through the atmosphere by molecules colliding with other molecules. Matter density in space around Earth is approximately 5 particles per cubic centimeter. You could assume those were 5 molecules of uranium, but the most reasonable assumption is that most of them are probably atomic hydrogen. You can also assume that the velocity of those particles from the solar wind as being a constant pressure and any variation of that pressure being the actual "sounds" of the sun being carried by the solar wind. Bcjochim07 asked back in 2008 what particle density was at sea level on this site, https://www.physicsforums.com/threads/number-density-of-air.232162/, which works out to a density of 2.7*10^19 molecules per cubic centimeter.

    I'll say it's theoretically possible to use sensors out in space to detect changes in pressure waves from the sun, but it's going to be somewhere on the order of 10^19th fainter than any sound we can detect at sea level.
     
  11. Jan 24, 2017 #10
    First of all, sound pressure waves on the sun are extremely low frequency, of the order of hundreds of μHz, well outside the range of human hearing, so you wouldn't hear anything at all even if the sound could be transmitted to Earth. Secondly, they would not be transmitted even if a path existed, because they are trapped. They are reflected back down to the Sun once they penetrate to a distance of about 500 km above the visible surface. See Phillips, The Physics of the Sun.

    However, for the purposes of a thought experiment, let's assume that one is listening via a frequency converter, and that the space between Earth and Sun is filled with a medium that can transmit the waves without causing any physical calamity. The wave will be attenuated 6 dB for every doubling of distance from the Sun purely due to the spreading of the wavefront (not taking into account any losses due to our ficticious medium). If my maths is not letting me down, that amounts to a total attenuation of 46 dB by the time it gets to Earth. That's a lot, and I don't know what the starting amplitude of Sun pressure waves is, but it is probably not enough to make them inaudible. For instance, an aircraft jet engine at one metre has a sound pressure level of 150 dB. Attenuating that by 46 dB, it would still be loud enough to make you go deaf with long term exposure.

    Of course, any real medium will have losses which are likely to be more significant than that. According to the Wikipedia attenuation article, the attenuation coefficient of air is 1.64 dB/MHz-cm. I have no idea whether that figure, which is in the context of ultrasonics, is still valid at extremely low frequencies, but if it is, and again if my maths is not letting me down, the attenuation in the medium between Sun and Earth will be 2,400 dB. That's almost certainly enough to make the wave inaudible.
     
  12. Jan 24, 2017 #11
    Further to the above, p-waves on the sun have amplitudes in the hundreds of kilometres apparently. So going with 200 km and the mean density of the sun of 1.4, that translates to a peak pressure of 28×108 Pa, which translates to an SPL of 280 dB. So with an ideal lossless medium, that would arrive on Earth with an amplitude large enough to cause severe earthquakes, to say the least. With a realistic lossy medium the amplitude on arriving at Earth would be unmeasurably small.
     
  13. Jan 24, 2017 #12
    Would it be possible, on one of the space missions, say to Venus or Mercury, to get close enough to record the sound of the Sun more vividly?
     
  14. Jan 24, 2017 #13
    Last edited by a moderator: May 8, 2017
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