SOHO can image the sun's magnetosphere. I don't have the foggiest idea how they manage it, because at most a satellite can have a single compass, and measure one point in the magnetic field. I thought for a while that maybe they were using the Zeeman effect, but their image description says that "black and white indicat[e] opposite polarities." I don't think you could detect the direction of the field with Zeeman splitting, because the thermodynamic distributions should be isotropic in every variable, and there's nothing on the atom scale to compare the direction of the field against.

How does SOHO manage to image the magnetic field of the sun?


  • $\begingroup$ Your idea with the Zeeman effect is totally correct. You don't need anything to compare to than the average when you have the line shift(s). $\endgroup$ Jun 24 '20 at 1:34
  • $\begingroup$ @planetmaker Wouldn't a B vector in the +z direction look the same as a B vector in the -z direction? How can SOHO tell what the polarity is? $\endgroup$
    – Retracted
    Jun 24 '20 at 1:57
  • $\begingroup$ There is more detail derivable from it: en.m.wikipedia.org/wiki/Vector_magnetograph $\endgroup$ Jun 24 '20 at 9:19
  • 1
    $\begingroup$ I've no idea specifically how SOHO does it, but your statement about the Zeeman effect is (partially) incorrect when combined with polarimetry (there is still some ambiguity perpendicular to the line of sight). $\endgroup$
    – ProfRob
    Jun 24 '20 at 12:08
  • $\begingroup$ Possibly helpful nasa.gov/mission_pages/sunearth/news/solar-magnetism.html and hmi.stanford.edu $\endgroup$ Jun 24 '20 at 14:06

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