Recently, I came across the following picture from NASA's SOHO observatory:

enter image description here

It seems evident that this is a transverse wave (mind the ring which is bright and dark). But how can this be the case if the sun consists of gaseous matter?

  • 2
    $\begingroup$ Well, sound waves move through air. And some can be seen! Also, a shockwave caused by big booms also moves through air and looks pretty much like the picture (in air). Waves go through all mediums $\endgroup$ – Nitay Jul 1 '14 at 19:44
  • 2
    $\begingroup$ That doesn't really look like a transverse wave to me, looks like a circular wave. $\endgroup$ – Kyle Kanos Jul 1 '14 at 19:46
  • $\begingroup$ @KyleKanos - "transverse" means "the motion of the particles in the wave is up and down, not in the direction of wave propagation". So the fact that the wave front is circular doesn't change whether the wave is transverse or longitudinal. Sound waves are longitudinal - they can exist in gases. Transverse waves can only exist if the medium can support tensile or shear forces. $\endgroup$ – Floris Jul 1 '14 at 20:23
  • 1
    $\begingroup$ @Floris: I am well aware of what transverse means. The point of my comment is that OP is mistaken in thinking that it's a transverse wave because of its appearance, rather than thinking about what it is he is looking at. $\endgroup$ – Kyle Kanos Jul 1 '14 at 20:29
  • $\begingroup$ @KyleKanos - even with your clarification, I had to read both your comments about five times to extract the meaning that you meant to give it. You said "it looks like .. to me" to say "different people say different things about what it looks like but you need to think about the nature of the wave not the appearance". I can see now that your comment could have been read that way - but it honestly wasn't obvious to me. $\endgroup$ – Floris Jul 1 '14 at 20:36

I agree it looks like a transverse wave - like the ripples on a pond. But I believe you are fooled by a simple thing: the waves you are looking at look like "illuminated ripples" but are in reality just changes in temperature (changes in brightness of the sun's surface).

If you have a shock wave traveling out across the surface of the sun, what happens? The medium (solar plasma) will alternately be compressed and expanded. That is likely to affect the temperature - and I think that's what you are looking at here.

Now if you could somehow believe that there really were "surface ripples" on the sun's surface, that is really no different than the ripples in water on a pond: while the sun is a plasma (not a gas - not at that temperature), its particles are subject to considerable gravity. And the laws of motion for a wave traveling along the surface of a medium subjected to gravity really don't care about the state of matter of the medium - just the differential forces generated by a slope on the surface (which leads to wave propagation).

Either way there is no contradiction - but I'm pretty sure you are looking at changes in intensity/density, not a "transverse wave".

  • $\begingroup$ The article says "The solar seismic waves appear to be compression waves like the "P" waves generated by an earthquake." $\endgroup$ – mmesser314 Jul 2 '14 at 4:13
  • $\begingroup$ The key point is that if the wave were a longitudinal shock wave in a gas/plasma, it should have a three-dimensional spherical form, not just a ring spreading on a two-dimensional surface as it appears. The problem is that the standard model says the sun has no distinct surface, yet this picture strongly suggests it has. $\endgroup$ – ClassicalPhysicist Jul 2 '14 at 8:57
  • 1
    $\begingroup$ The wave may in fact be 3D - but if the temperature and density gradient is sufficient you will only see the wave "at the surface" - that is where the plasma is dense and hot enough to show this luminosity, but before there is too much absorption from intervening plasma - an "optical" surface. But this is speculation on my part. $\endgroup$ – Floris Jul 2 '14 at 14:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.