The sun is a big ball of gas, mostly hydrogen. That hydrogen undergoes fusion, producing both the radiation that keeps us warm and heavier atoms, mostly helium but also oxygen, carbon and other elements. (You can find a good lesson about the sun here.)
Our sun has an atmosphere, though you can't see it most of the time. The chromosphere, a think pink layer, can sometimes be seen during an eclipse, when the moon is blocking out the sun's disk. But you're more likely to notice the corona. To the naked eye (though you shouldn't view an eclipse without some sort of help), the corona appears white.
To scientists, though, the different wavelengths of light in the corona give them information about what is going on there. An international team of astrophysicists observed eclipses in 2006, 2008 (above) and 2009; they presented their findings at this week's American Astronomical Society meeting. The red, blue and green colors in their corona images represent wavelengths of light produced by iron ions. Though scientists have known that the ions were in the corona, this is the first time that they have mapped their distribution. This mapping could lead to more insight into the corona and how the sun's behavior affects Earth.
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( Image credit: Shadia Habbal et al.)