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Name: Ernest
Status: educator
Grade: 6-8
Location: VA
Country: N/A
Date: 4/6/2005


Question:
How do we know the amount (relative percentage) of a given gas present in a star? Is there a way to determine this with emission spectra?


Replies:
The relative amounts of various gaseous substances in stars is determined from the spectra of the star "light". I use the term "light" in quotes to indicate that the radiation is all inclusive, not just visible light. It could be x-ray, ultraviolet, infrared, microwave, in addition to visible light. The "light" is separated using some sort of instrument that spreads the "light" by wavelength (or frequency). Since each substance has a characteristic "fingerprint" of radiation, the various gases can be identified (after the red shift and some other corrections are applied to the observed spectra). The "fingerprints" can be calibrated using laboratory experiments so that the relative intensities can be determined independently. This allows an estimate of the star temperature. Both emission and absorption spectra (by the cooler outer atmosphere of the star) are used to determine the relative abundances.

Vince Calder



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