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.
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