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How can we know/check the sun's current and latest chemical composition?

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kweba
#1
Mar8-12, 10:48 PM
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Hello! We know that the sun started with about more than 70% Hydrogen and more than 20% Helium. with other metals consisting the remaining few percent. Now throughout its lifetime, this composition changes, especially with regards to the hydrogen in its core because of nuclear reactions. Correct?


So how do astronomers/astrophysicists able to do a "reading" or analysis about the sun's current chemical composition?


I learned and had read about scientists looking at the spectrum of the sun (as well as other stars), and this spectrum shows colors that represent particular elements (ie red for hydrogen), is this correct?

If so, how do they do this? Do they just take a picture of the sun or something? How can they tell what element is the most abundant and what are the other elements' percentage? And what is this kind of analysis called?

Thank you in advance and sorry for my ignorance and incorrect use of words/terms :)
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Simon Bridge
#2
Mar9-12, 01:38 AM
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I learned and had read about scientists looking at the spectrum of the sun (as well as other stars), and this spectrum shows colors that represent particular elements (ie red for hydrogen), is this correct?
Basically - but it is more that the light from the inside of the Sun gets absorbed at characteristic wavelengths - creating this dark bands in the spectrum. The pattern of bands depends on the electron configuration of the elements ... which depends on what sort of atom you have. You can google for "absorbtion spectra".

If so, how do they do this? Do they just take a picture of the sun or something?
Pretty much. We point a pinhole camera at the sun, and put the resulting beam through a prism, or a diffraction grating, and take a photo of that. The device is called a "spectrometer". You get a picture kinda like this:
eg.
The C, F, G and h lines are characteristic of Hydrogen.
The D lines (the double-ones in orange) are from Sodium - you know: sodium lamps?
How can they tell what element is the most abundant and what are the other elements' percentage?
By the relative strengths of the lines ... the more of the light at those wavelengths that gets absorbed, the more of that element there is.
And what is this kind of analysis called?
spectroscopy or spectral analysis.

We can also check the results in a lab just by heating up different elements and doing the same analysis. Pretty much everything we know about stars comes from their light.

Anyway - that should give you a starting point.
davenn
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Mar9-12, 02:43 AM
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Great intro for the OP, Simon :)

OP also do some google searching on Fraunhofer lines, which are what those dark absorption lines are called

Dave

twofish-quant
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Mar9-12, 03:01 AM
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How can we know/check the sun's current and latest chemical composition?

Quote Quote by kweba View Post
If so, how do they do this? Do they just take a picture of the sun or something? How can they tell what element is the most abundant and what are the other elements' percentage? And what is this kind of analysis called?
Spectroscopy will get you the composition on the surface of the sun.

Now to get the composition in the **core** of the sun, you have to be a bit more clever. There is a field called helioseismology, that looks at how waves go through the sun.

http://en.wikipedia.org/wiki/Helioseismology

This will let you get a temperature, density, and pressure profile of the sun and then you compare with computer calculations to see if they match up. One problem with looking at the surface of the sun, is that there is no nuclear fusion going on there so you don't actually see an increased amount of helium that comes from burning hydrogen.
phyzguy
#5
Mar9-12, 05:15 AM
P: 2,179
We can also see what's happening in the core of the sun more directly by looking at neutrinos coming from the sun's core. Because neutrinos interact so little with matter, they basically fly freely out from the core of the sun and can be measured here on Earth with sensitive detectors. Here is a link to a recent article on this.


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