4 ms·

How do they measure it? There was nothing in the article about how this is observed?

fsckin 13y ago
It's an inset picture and link[0]. They collect quite a bit of data[1] (that you can ask for[2]). "Astronomers at the Wilcox Solar Observatory (WSO) monitor the sun's global magnetic field on a daily basis." [0] http://wso.stanford.edu/ http://wso.stanford.edu/ [1] http://wso.stanford.edu/words/plots.info http://wso.stanford.edu/words/plots.info [2] http://wso.stanford.edu/forms/prsyn.html http://wso.stanford.edu/forms/prsyn.html
laumars 13y ago
They fired a load of iron filings at the sun.
gngeal 13y ago
Observing the behavior of plasma around the Sun is probably one of the indicators. Also, the Zeeman effect in the Sun's spectrum measures the absolute intensity quite directly; I'd assume that the zero transition could be observable this way.
- mturmon 13y ago
  Once they observe the photospheric magnetic field, they use it as a boundary condition for models that project upward into the corona. They can't observe the field directly in the corona (this might be an experimental capability somewhere, but it is not done observationally anywhere). They do observe the movement of plasma in the corona, to check the field lines predicted by the models.
mturmon 13y ago
Good question. The light spectrum emitted by the Sun has "spectral lines", or emission features (deep dips or strong peaks) that are determined by light-absorption or light-emission from specific elements (e.g., Nickel, Iron, and of course Hydrogen) in the Sun's atmosphere. If the little packet of stuff that was absorbing light is moving toward or away from you, the characteristic frequencies of all its spectral lines will be Doppler shifted. So, you can measure the velocity of that packet of stuff by seeing how much the line is shifted. Since you have a lot of photons, you can do this independently across the Sun's surface and get a spatially-resolved map of velocity ("Dopplergram", http://solar-center.stanford.edu/dopplergram.html http://solar-center.stanford.edu/dopplergram.html). If the little packet of stuff was in a magnetic field, its spectral lines will be split into sub-lines due to the Zeeman effect. So, you can also measure the spatially-resolved magnetic field of the Sun, and this is called a "magnetogram". It is kind of surprising that this measurement can be made at all.
- brittohalloran 13y ago
  Doppler shift. One of the simplest and most deeply useful physics principles. Things you learned in high school that are actually useful way down the road. Basic trigonometry (Sohcahtoa) falls in the same category for me.
  - mturmon 13y ago
    So true. I have been watching an excellent lecture series by Prof. Charles Bailyn (Yale U.) where he goes into some current work in astrophysics (2007) using calculus-free physics. (It's at http://oyc.yale.edu/astronomy/astr-160 http://oyc.yale.edu/astronomy/astr-160, and other places like iTunes U.) It's amazing how deeply useful Doppler shift is; he returns to it thematically at least twice, talking about exoplanets as well as black holes. "We can't see them directly, but we can see them through the way they interact with other things."

It's an inset picture and link[0]. They collect quite a bit of data[1] (that you can ask for[2]). "Astronomers at the Wilcox Solar Observatory (WSO) monitor the sun's global magnetic field on a daily basis." [0] http://wso.stanford.edu/ http://wso.stanford.edu/ [1] http://wso.stanford.edu/words/plots.info http://wso.stanford.edu/words/plots.info [2] http://wso.stanford.edu/forms/prsyn.html http://wso.stanford.edu/forms/prsyn.html

laumars 13y ago

They fired a load of iron filings at the sun.

gngeal 13y ago

Observing the behavior of plasma around the Sun is probably one of the indicators. Also, the Zeeman effect in the Sun's spectrum measures the absolute intensity quite directly; I'd assume that the zero transition could be observable this way.

mturmon 13y ago
Once they observe the photospheric magnetic field, they use it as a boundary condition for models that project upward into the corona. They can't observe the field directly in the corona (this might be an experimental capability somewhere, but it is not done observationally anywhere). They do observe the movement of plasma in the corona, to check the field lines predicted by the models.

mturmon 13y ago

Good question. The light spectrum emitted by the Sun has "spectral lines", or emission features (deep dips or strong peaks) that are determined by light-absorption or light-emission from specific elements (e.g., Nickel, Iron, and of course Hydrogen) in the Sun's atmosphere. If the little packet of stuff that was absorbing light is moving toward or away from you, the characteristic frequencies of all its spectral lines will be Doppler shifted. So, you can measure the velocity of that packet of stuff by seeing how much the line is shifted. Since you have a lot of photons, you can do this independently across the Sun's surface and get a spatially-resolved map of velocity ("Dopplergram", http://solar-center.stanford.edu/dopplergram.html http://solar-center.stanford.edu/dopplergram.html). If the little packet of stuff was in a magnetic field, its spectral lines will be split into sub-lines due to the Zeeman effect. So, you can also measure the spatially-resolved magnetic field of the Sun, and this is called a "magnetogram". It is kind of surprising that this measurement can be made at all.

brittohalloran 13y ago
Doppler shift. One of the simplest and most deeply useful physics principles. Things you learned in high school that are actually useful way down the road. Basic trigonometry (Sohcahtoa) falls in the same category for me.
- mturmon 13y ago
  So true. I have been watching an excellent lecture series by Prof. Charles Bailyn (Yale U.) where he goes into some current work in astrophysics (2007) using calculus-free physics. (It's at http://oyc.yale.edu/astronomy/astr-160 http://oyc.yale.edu/astronomy/astr-160, and other places like iTunes U.) It's amazing how deeply useful Doppler shift is; he returns to it thematically at least twice, talking about exoplanets as well as black holes. "We can't see them directly, but we can see them through the way they interact with other things."