<p>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 &quot;black and white indicat[e] opposite polarities.&quot; 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.</p>
<p>How does SOHO manage to image the magnetic field of the sun?</p>
<p><a href="https://sohowww.nascom.nasa.gov/data/realtime/image-description.html" rel="noreferrer">https://sohowww.nascom.nasa.gov/data/realtime/image-description.html</a></p>

CC BY-SA 4.0
2020-06-24T01:34:34.480Z
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).
planetmaker
CC BY-SA 4.0
2020-06-24T01:57:59.260Z
@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?
Retracted
CC BY-SA 4.0
2020-06-24T09:19:35.190Z
There is more detail derivable from it: https://en.m.wikipedia.org/wiki/Vector_magnetograph
planetmaker
CC BY-SA 4.0
2020-06-24T12:08:49.943Z
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).
ProfRob
CC BY-SA 4.0
2020-06-24T14:06:22.920Z
Possibly helpful  https://www.nasa.gov/mission_pages/sunearth/news/solar-magnetism.html   and    http://hmi.stanford.edu/
Carl Witthoft
CC BY-SA 4.0
2020-06-24T23:32:47.700Z
@robJeffries exactly that is explained on the linked page... Though I read it as the ambiguity is in the perpendicular component, but unambiguous in LOS.
planetmaker
CC BY-SA 4.0
2021-11-24T15:42:41.213Z
It does use the Zeeman effect but can only get reliable info directly along the lines of sight.  Thus, the accuracy drops considerably at the limbs of the Sun.
honeste_vivere
<the-sun><stellar-astrophysics><soho>
How does SOHO know what's going on in the sun's magnetic feild?
Retracted
# How does SOHO know what's going on in the sun's magnetic feild?

(Asked by: username_0 on 2020-06-24)

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?

<https://sohowww.nascom.nasa.gov/data/realtime/image-description.html>

**Tags:** the-sun, stellar-astrophysics, soho
> **Comments:**
> **username_1**: 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).  
> **username_0**: @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?  
> **username_1**: There is more detail derivable from it: https://en.m.wikipedia.org/wiki/Vector_magnetograph  
> **username_2**: 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).  
> **username_3**: Possibly helpful  https://www.nasa.gov/mission_pages/sunearth/news/solar-magnetism.html   and    http://hmi.stanford.edu/  
> **username_1**: @robJeffries exactly that is explained on the linked page... Though I read it as the ambiguity is in the perpendicular component, but unambiguous in LOS.  
> **username_4**: It does use the Zeeman effect but can only get reliable info directly along the lines of sight.  Thus, the accuracy drops considerably at the limbs of the Sun.  

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