The Sun
The Sun
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For introductory and general information about the Sun, try links in the first two sections (Solar System and Sun websites). Sections further below focus on particular sub-topics. However, topics are very interelated. You might like to browse across related topics.
Nearest Star- The Surprising Science of Our
Sun
For an excellent discussion for beginners about how the interior of stars are modeled
see
100 Billion Suns--The Birth, Life, and Death of the Stars
by Rudolph Kippenhahn. Basic Books. Written by a pioneer of the field.
When you see diagrams which show you the interior of the Sun, where does that
information come from? Actually, we cannot look inside. We generally must infer
what happens by measuring properties we see at the "surface";
and we can measure the light and particles that are emmitted out.
For many years, from just using that information, a very simple theoretical technique has been
used to calculate what happens inside the sun. It is called a one dimensional
hydrodynamic model. Simply, the physical conditions along a radial line between the
center and the surface are calculated. If you know the conditions at the surface (the
"boundary conditions") and if you know how big the star is,
you can then calculate everything else below. This technique
has very successfully predicted the nuclear burning conditions required at the center
of the sun and the energy output.* This technique also works well for
calculating properties of Main Sequence stars and
stars slightly evolved off the Main Sequence. (The interiors of
highly evolved stars, though, seem to be too complex for this technique to work).**
However, the one dimensional hydrodynamic model is an approximation. It doesn't tell us in
detail what may happen inside. Instead it assumes that some details are unimportant.
That's why Helioseismology is so important.
It is a way to probe the interior of the sun with direct observational
evidence. The Sun vibrates with regularly patterned acoustic waves. As with earthquakes in the
Earth, these waves are directly dependent on the physical conditions the waves must pass through.
Therefore, measuring the properties of these waves gives us a more direct
measurement of the conditions and structure inside. Of course, we can't go to the Sun
to measure the waves. Instead, we measure the variations in the light that come to us.
Astrophysicists who work with
Helioseismology hope they will be able to give better tests to current theories.
(One of the most enlightening astrophysics colloquium I've
gone to was by a helioseismologist at Cambridge.)
*[Until recently, the The Solar Neutrino Problem suggested that the
measured output of solar neutrinos did not match the predictions of existing
theory. However, that problem seems to have been resolved with more sophisticated
measurements and modeling of neutrino behavior. For that story see the
The Solar Neutrino Problem above. ]
**[For an excellent discussion for beginners about how the interior of stars are modeled
see Rudolph Kippenhahn's book,
100 Billion Suns--The Birth, Life, and Death of the Stars.]
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